1BASH(1)                     General Commands Manual                    BASH(1)
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3
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NAME

6       bash - GNU Bourne-Again SHell
7

SYNOPSIS

9       bash [options] [command_string | file]
10
12       Bash is Copyright (C) 1989-2018 by the Free Software Foundation, Inc.
13

DESCRIPTION

15       Bash  is  an  sh-compatible  command language interpreter that executes
16       commands read from the standard input or from a file.  Bash also incor‐
17       porates useful features from the Korn and C shells (ksh and csh).
18
19       Bash  is  intended  to  be a conformant implementation of the Shell and
20       Utilities portion  of  the  IEEE  POSIX  specification  (IEEE  Standard
21       1003.1).  Bash can be configured to be POSIX-conformant by default.
22

OPTIONS

24       All of the single-character shell options documented in the description
25       of the set builtin command, including -o, can be used as  options  when
26       the  shell  is  invoked.   In  addition,  bash interprets the following
27       options when it is invoked:
28
29       -c        If the -c option is present, then commands are read from  the
30                 first non-option argument command_string.  If there are argu‐
31                 ments  after  the  command_string,  the  first  argument   is
32                 assigned  to  $0  and any remaining arguments are assigned to
33                 the positional parameters.  The assignment  to  $0  sets  the
34                 name  of  the  shell, which is used in warning and error mes‐
35                 sages.
36       -i        If the -i option is present, the shell is interactive.
37       -l        Make bash act as if it had been invoked as a login shell (see
38                 INVOCATION below).
39       -r        If  the  -r  option  is present, the shell becomes restricted
40                 (see RESTRICTED SHELL below).
41       -s        If the -s option is present, or if no arguments remain  after
42                 option  processing,  then commands are read from the standard
43                 input.  This option allows the positional  parameters  to  be
44                 set  when invoking an interactive shell or when reading input
45                 through a pipe.
46       -D        A list of all double-quoted strings preceded by $ is  printed
47                 on  the standard output.  These are the strings that are sub‐
48                 ject to language translation when the current locale is not C
49                 or  POSIX.   This  implies the -n option; no commands will be
50                 executed.
51       [-+]O [shopt_option]
52                 shopt_option is one of the  shell  options  accepted  by  the
53                 shopt   builtin  (see  SHELL  BUILTIN  COMMANDS  below).   If
54                 shopt_option is present, -O sets the value of that option; +O
55                 unsets  it.   If  shopt_option is not supplied, the names and
56                 values of the shell options accepted by shopt are printed  on
57                 the  standard  output.   If  the invocation option is +O, the
58                 output is displayed in a format that may be reused as input.
59       --        A -- signals the end of options and disables  further  option
60                 processing.   Any arguments after the -- are treated as file‐
61                 names and arguments.  An argument of - is equivalent to --.
62
63       Bash also  interprets  a  number  of  multi-character  options.   These
64       options  must  appear  on  the command line before the single-character
65       options to be recognized.
66
67       --debugger
68              Arrange for the debugger profile to be executed before the shell
69              starts.   Turns  on extended debugging mode (see the description
70              of the extdebug option to the shopt builtin below).
71       --dump-po-strings
72              Equivalent to -D, but the output is in the GNU gettext po  (por‐
73              table object) file format.
74       --dump-strings
75              Equivalent to -D.
76       --help Display  a  usage  message  on standard output and exit success‐
77              fully.
78       --init-file file
79       --rcfile file
80              Execute commands from file instead of the standard personal ini‐
81              tialization  file  ~/.bashrc  if  the  shell is interactive (see
82              INVOCATION below).
83
84       --login
85              Equivalent to -l.
86
87       --noediting
88              Do not use the GNU readline library to read command  lines  when
89              the shell is interactive.
90
91       --noprofile
92              Do  not read either the system-wide startup file /etc/profile or
93              any  of  the  personal  initialization  files   ~/.bash_profile,
94              ~/.bash_login,  or  ~/.profile.   By  default,  bash reads these
95              files when it is  invoked  as  a  login  shell  (see  INVOCATION
96              below).
97
98       --norc Do  not  read  and  execute  the  personal  initialization  file
99              ~/.bashrc if the shell is interactive.  This  option  is  on  by
100              default if the shell is invoked as sh.
101
102       --posix
103              Change  the behavior of bash where the default operation differs
104              from the POSIX standard to match the standard (posix mode).  See
105              SEE  ALSO  below  for a reference to a document that details how
106              posix mode affects bash's behavior.
107
108       --restricted
109              The shell becomes restricted (see RESTRICTED SHELL below).
110
111       --rpm-requires
112              Produce the list of files that are required for the shell script
113              to  run.   This  implies '-n' and is subject to the same limita‐
114              tions as compile time error checking checking; Command substitu‐
115              tions,  Conditional  expressions and eval builtin are not parsed
116              so some dependencies may be missed.
117
118       --verbose
119              Equivalent to -v.
120
121       --version
122              Show version information for this instance of bash on the  stan‐
123              dard output and exit successfully.
124

ARGUMENTS

126       If arguments remain after option processing, and neither the -c nor the
127       -s option has been supplied, the first argument is assumed  to  be  the
128       name  of  a file containing shell commands.  If bash is invoked in this
129       fashion, $0 is set to the name of the file, and the positional  parame‐
130       ters  are set to the remaining arguments.  Bash reads and executes com‐
131       mands from this file, then exits.  Bash's exit status is the exit  sta‐
132       tus  of  the  last  command executed in the script.  If no commands are
133       executed, the exit status is 0.  An attempt is first made to  open  the
134       file in the current directory, and, if no file is found, then the shell
135       searches the directories in PATH for the script.
136

INVOCATION

138       A login shell is one whose first character of argument zero is a -,  or
139       one started with the --login option.
140
141       An  interactive  shell  is  one  started  without  non-option arguments
142       (unless -s is specified) and without the -c option whose standard input
143       and error are both connected to terminals (as determined by isatty(3)),
144       or one started with the -i option.  PS1 is set and  $-  includes  i  if
145       bash  is interactive, allowing a shell script or a startup file to test
146       this state.
147
148       The following paragraphs describe how bash executes its startup  files.
149       If  any  of  the files exist but cannot be read, bash reports an error.
150       Tildes are expanded in filenames as described below under Tilde  Expan‐
151       sion in the EXPANSION section.
152
153       When  bash is invoked as an interactive login shell, or as a non-inter‐
154       active shell with the --login option, it first reads and executes  com‐
155       mands  from  the file /etc/profile, if that file exists.  After reading
156       that file, it looks for ~/.bash_profile, ~/.bash_login, and ~/.profile,
157       in  that order, and reads and executes commands from the first one that
158       exists and is readable.  The --noprofile option may be  used  when  the
159       shell is started to inhibit this behavior.
160
161       When an interactive login shell exits, or a non-interactive login shell
162       executes the exit builtin command, bash  reads  and  executes  commands
163       from  the  files ~/.bash_logout and /etc/bash.bash_logout, if the files
164       exists.
165
166       When an interactive shell that is not a login shell  is  started,  bash
167       reads  and executes commands from ~/.bashrc, if that file exists.  This
168       may be inhibited by using the --norc option.  The --rcfile file  option
169       will  force  bash  to  read  and  execute commands from file instead of
170       ~/.bashrc.
171
172       When bash is started non-interactively, to  run  a  shell  script,  for
173       example, it looks for the variable BASH_ENV in the environment, expands
174       its value if it appears there, and uses the expanded value as the  name
175       of  a  file to read and execute.  Bash behaves as if the following com‐
176       mand were executed:
177              if [ -n "$BASH_ENV" ]; then . "$BASH_ENV"; fi
178       but the value of the PATH variable is not used to search for the  file‐
179       name.
180
181       If  bash  is  invoked  with  the name sh, it tries to mimic the startup
182       behavior of historical versions of sh as  closely  as  possible,  while
183       conforming  to the POSIX standard as well.  When invoked as an interac‐
184       tive login shell, or a non-interactive shell with the  --login  option,
185       it  first  attempts  to read and execute commands from /etc/profile and
186       ~/.profile, in that order.  The  --noprofile  option  may  be  used  to
187       inhibit  this  behavior.  When invoked as an interactive shell with the
188       name sh, bash looks for the variable ENV, expands its value  if  it  is
189       defined,  and uses the expanded value as the name of a file to read and
190       execute.  Since a shell invoked as sh does not attempt to read and exe‐
191       cute  commands from any other startup files, the --rcfile option has no
192       effect.  A non-interactive shell invoked with  the  name  sh  does  not
193       attempt  to  read  any  other  startup files.  When invoked as sh, bash
194       enters posix mode after the startup files are read.
195
196       When bash is started in posix mode, as with the  --posix  command  line
197       option, it follows the POSIX standard for startup files.  In this mode,
198       interactive shells expand the ENV variable and commands  are  read  and
199       executed  from  the  file  whose  name is the expanded value.  No other
200       startup files are read.
201
202       Bash attempts to determine when it is being run with its standard input
203       connected to a network connection, as when executed by the remote shell
204       daemon, usually rshd, or the secure shell daemon sshd.  If bash  deter‐
205       mines  it  is being run in this fashion, it reads and executes commands
206       from ~/.bashrc, if that file exists and is readable.  It  will  not  do
207       this  if  invoked as sh.  The --norc option may be used to inhibit this
208       behavior, and the --rcfile option may be used to force another file  to
209       be  read,  but  neither  rshd  nor sshd generally invoke the shell with
210       those options or allow them to be specified.
211
212       If the shell is started with the effective user (group) id not equal to
213       the real user (group) id, and the -p option is not supplied, no startup
214       files are read, shell functions are not inherited from the environment,
215       the  SHELLOPTS,  BASHOPTS,  CDPATH,  and  GLOBIGNORE variables, if they
216       appear in the environment, are ignored, and the effective  user  id  is
217       set  to  the real user id.  If the -p option is supplied at invocation,
218       the startup behavior is the same, but the  effective  user  id  is  not
219       reset.
220

DEFINITIONS

222       The  following  definitions  are used throughout the rest of this docu‐
223       ment.
224       blank  A space or tab.
225       word   A sequence of characters considered as  a  single  unit  by  the
226              shell.  Also known as a token.
227       name   A  word  consisting  only  of alphanumeric characters and under‐
228              scores, and beginning with an alphabetic character or an  under‐
229              score.  Also referred to as an identifier.
230       metacharacter
231              A  character  that,  when unquoted, separates words.  One of the
232              following:
233              |  & ; ( ) < > space tab newline
234       control operator
235              A token that performs a control function.  It is one of the fol‐
236              lowing symbols:
237              || & && ; ;; ;& ;;& ( ) | |& <newline>
238

RESERVED WORDS

240       Reserved words are words that have a special meaning to the shell.  The
241       following words are recognized as reserved when unquoted and either the
242       first  word  of a simple command (see SHELL GRAMMAR below) or the third
243       word of a case or for command:
244
245       ! case  coproc  do done elif else esac fi for  function  if  in  select
246       then until while { } time [[ ]]
247

SHELL GRAMMAR

249   Simple Commands
250       A  simple  command  is a sequence of optional variable assignments fol‐
251       lowed by blank-separated words and redirections, and  terminated  by  a
252       control operator.  The first word specifies the command to be executed,
253       and is passed as argument zero.  The  remaining  words  are  passed  as
254       arguments to the invoked command.
255
256       The  return  value  of a simple command is its exit status, or 128+n if
257       the command is terminated by signal n.
258
259   Pipelines
260       A pipeline is a sequence of one or more commands separated  by  one  of
261       the control operators | or |&.  The format for a pipeline is:
262
263              [time [-p]] [ ! ] command [ [||&] command2 ... ]
264
265       The  standard output of command is connected via a pipe to the standard
266       input of command2.  This connection is performed  before  any  redirec‐
267       tions specified by the command (see REDIRECTION below).  If |& is used,
268       command's standard error, in addition to its standard output,  is  con‐
269       nected  to  command2's standard input through the pipe; it is shorthand
270       for 2>&1 |.  This implicit redirection of the  standard  error  to  the
271       standard  output  is  performed after any redirections specified by the
272       command.
273
274       The return status of a pipeline is the exit status of the last command,
275       unless  the  pipefail  option  is enabled.  If pipefail is enabled, the
276       pipeline's return status is the value of the last  (rightmost)  command
277       to  exit  with a non-zero status, or zero if all commands exit success‐
278       fully.  If the reserved word !  precedes a pipeline, the exit status of
279       that  pipeline  is the logical negation of the exit status as described
280       above.  The shell waits for all commands in the pipeline  to  terminate
281       before returning a value.
282
283       If  the  time reserved word precedes a pipeline, the elapsed as well as
284       user and system time consumed by its execution are  reported  when  the
285       pipeline  terminates.   The -p option changes the output format to that
286       specified by POSIX.  When the shell is in posix mode, it does not  rec‐
287       ognize  time  as  a  reserved word if the next token begins with a `-'.
288       The TIMEFORMAT variable may be set to a format  string  that  specifies
289       how  the timing information should be displayed; see the description of
290       TIMEFORMAT under Shell Variables below.
291
292       When the shell is in posix mode, time may be followed by a newline.  In
293       this  case,  the shell displays the total user and system time consumed
294       by the shell and its children.  The TIMEFORMAT variable may be used  to
295       specify the format of the time information.
296
297       Each  command in a pipeline is executed as a separate process (i.e., in
298       a subshell).  See COMMAND EXECUTION ENVIRONMENT for a description of  a
299       subshell  environment.   If  the  lastpipe  option is enabled using the
300       shopt builtin (see the description of shopt below), the last element of
301       a pipeline may be run by the shell process.
302
303   Lists
304       A  list  is a sequence of one or more pipelines separated by one of the
305       operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
306       <newline>.
307
308       Of these list operators, && and || have equal precedence, followed by ;
309       and &, which have equal precedence.
310
311       A sequence of one or more newlines may appear in a list  instead  of  a
312       semicolon to delimit commands.
313
314       If  a  command  is terminated by the control operator &, the shell exe‐
315       cutes the command in the background in a subshell.  The shell does  not
316       wait  for the command to finish, and the return status is 0.  These are
317       referred to as asynchronous commands.  Commands separated by  a  ;  are
318       executed sequentially; the shell waits for each command to terminate in
319       turn.  The return status is the exit status of the  last  command  exe‐
320       cuted.
321
322       AND  and  OR  lists are sequences of one or more pipelines separated by
323       the && and || control operators, respectively.  AND and  OR  lists  are
324       executed with left associativity.  An AND list has the form
325
326              command1 && command2
327
328       command2  is  executed if, and only if, command1 returns an exit status
329       of zero (success).
330
331       An OR list has the form
332
333              command1 || command2
334
335       command2 is executed if, and only if, command1 returns a non-zero  exit
336       status.   The  return  status of AND and OR lists is the exit status of
337       the last command executed in the list.
338
339   Compound Commands
340       A compound command is one of the following.  In most cases a list in  a
341       command's  description may be separated from the rest of the command by
342       one or more newlines, and may be followed by a newline in  place  of  a
343       semicolon.
344
345       (list) list  is  executed in a subshell environment (see COMMAND EXECU‐
346              TION ENVIRONMENT below).  Variable assignments and builtin  com‐
347              mands  that  affect  the  shell's  environment  do not remain in
348              effect after the command completes.  The return  status  is  the
349              exit status of list.
350
351       { list; }
352              list  is simply executed in the current shell environment.  list
353              must be terminated with a newline or semicolon.  This  is  known
354              as  a  group  command.   The return status is the exit status of
355              list.  Note that unlike the metacharacters ( and ), { and }  are
356              reserved words and must occur where a reserved word is permitted
357              to be recognized.  Since they do not cause a  word  break,  they
358              must  be  separated  from  list  by  whitespace or another shell
359              metacharacter.
360
361       ((expression))
362              The expression is evaluated according  to  the  rules  described
363              below  under ARITHMETIC EVALUATION.  If the value of the expres‐
364              sion is non-zero, the return status is 0; otherwise  the  return
365              status is 1.  This is exactly equivalent to let "expression".
366
367       [[ expression ]]
368              Return  a  status  of  0 or 1 depending on the evaluation of the
369              conditional expression expression.  Expressions are composed  of
370              the  primaries  described  below  under CONDITIONAL EXPRESSIONS.
371              Word splitting and pathname expansion are not performed  on  the
372              words  between  the  [[  and  ]]; tilde expansion, parameter and
373              variable expansion, arithmetic expansion, command  substitution,
374              process  substitution,  and quote removal are performed.  Condi‐
375              tional operators such as -f must be unquoted to be recognized as
376              primaries.
377
378              When  used with [[, the < and > operators sort lexicographically
379              using the current locale.
380
381              When the == and != operators are used, the string to  the  right
382              of the operator is considered a pattern and matched according to
383              the rules described below under Pattern Matching, as if the ext‐
384              glob shell option were enabled.  The = operator is equivalent to
385              ==.  If the nocasematch shell option is enabled,  the  match  is
386              performed  without  regard to the case of alphabetic characters.
387              The return value is 0 if the string matches  (==)  or  does  not
388              match  (!=)  the pattern, and 1 otherwise.  Any part of the pat‐
389              tern may be quoted to force the quoted portion to be matched  as
390              a string.
391
392              An  additional  binary operator, =~, is available, with the same
393              precedence as == and !=.  When it is used,  the  string  to  the
394              right  of  the  operator  is considered a POSIX extended regular
395              expression and matched accordingly (as in regex(3)).  The return
396              value  is  0 if the string matches the pattern, and 1 otherwise.
397              If the regular expression is syntactically incorrect, the condi‐
398              tional expression's return value is 2.  If the nocasematch shell
399              option is enabled, the match is performed without regard to  the
400              case  of  alphabetic characters.  Any part of the pattern may be
401              quoted to force the quoted portion to be matched  as  a  string.
402              Bracket expressions in regular expressions must be treated care‐
403              fully, since  normal  quoting  characters  lose  their  meanings
404              between brackets.  If the pattern is stored in a shell variable,
405              quoting the variable expansion forces the entire pattern  to  be
406              matched as a string.  Substrings matched by parenthesized subex‐
407              pressions within the regular expression are saved in  the  array
408              variable BASH_REMATCH.  The element of BASH_REMATCH with index 0
409              is the portion of the string matching the entire regular expres‐
410              sion.   The  element of BASH_REMATCH with index n is the portion
411              of the string matching the nth parenthesized subexpression.
412
413              Expressions may  be  combined  using  the  following  operators,
414              listed in decreasing order of precedence:
415
416              ( expression )
417                     Returns  the  value  of  expression.  This may be used to
418                     override the normal precedence of operators.
419              ! expression
420                     True if expression is false.
421              expression1 && expression2
422                     True if both expression1 and expression2 are true.
423              expression1 || expression2
424                     True if either expression1 or expression2 is true.
425
426              The && and || operators do not evaluate expression2 if the value
427              of  expression1  is  sufficient to determine the return value of
428              the entire conditional expression.
429
430       for name [ [ in [ word ... ] ] ; ] do list ; done
431              The list of words following in is expanded, generating a list of
432              items.  The variable name is set to each element of this list in
433              turn, and list is executed each time.  If the in word  is  omit‐
434              ted,  the  for  command  executes  list once for each positional
435              parameter that is set (see PARAMETERS below).  The return status
436              is  the  exit  status of the last command that executes.  If the
437              expansion of the items following in results in an empty list, no
438              commands are executed, and the return status is 0.
439
440       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
441              First, the arithmetic expression expr1 is evaluated according to
442              the rules described  below  under  ARITHMETIC  EVALUATION.   The
443              arithmetic  expression  expr2 is then evaluated repeatedly until
444              it evaluates to zero.  Each time expr2 evaluates to  a  non-zero
445              value,  list  is executed and the arithmetic expression expr3 is
446              evaluated.  If any expression is omitted, it behaves  as  if  it
447              evaluates to 1.  The return value is the exit status of the last
448              command in list that is executed, or false if any of the expres‐
449              sions is invalid.
450
451       select name [ in word ] ; do list ; done
452              The list of words following in is expanded, generating a list of
453              items.  The set of expanded words is  printed  on  the  standard
454              error,  each  preceded  by a number.  If the in word is omitted,
455              the positional parameters are printed  (see  PARAMETERS  below).
456              The  PS3 prompt is then displayed and a line read from the stan‐
457              dard input.  If the line consists of a number  corresponding  to
458              one  of  the  displayed  words, then the value of name is set to
459              that word.  If the line is empty, the words and prompt are  dis‐
460              played again.  If EOF is read, the command completes.  Any other
461              value read causes name to be set to  null.   The  line  read  is
462              saved  in  the  variable REPLY.  The list is executed after each
463              selection until a break command is executed.  The exit status of
464              select  is the exit status of the last command executed in list,
465              or zero if no commands were executed.
466
467       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
468              A case command first expands word, and tries to match it against
469              each  pattern  in turn, using the matching rules described under
470              Pattern Matching below.  The word is expanded using tilde expan‐
471              sion,  parameter  and  variable expansion, arithmetic expansion,
472              command substitution, process substitution  and  quote  removal.
473              Each pattern examined is expanded using tilde expansion, parame‐
474              ter and variable expansion, arithmetic expansion,  command  sub‐
475              stitution,  and  process substitution.  If the nocasematch shell
476              option is enabled, the match is performed without regard to  the
477              case  of alphabetic characters.  When a match is found, the cor‐
478              responding list is executed.  If the ;;  operator  is  used,  no
479              subsequent  matches are attempted after the first pattern match.
480              Using ;& in place of ;; causes execution to  continue  with  the
481              list  associated  with  the  next set of patterns.  Using ;;& in
482              place of ;; causes the shell to test the next  pattern  list  in
483              the statement, if any, and execute any associated list on a suc‐
484              cessful match.  The exit status is zero if no  pattern  matches.
485              Otherwise, it is the exit status of the last command executed in
486              list.
487
488       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
489              The if list is executed.  If its exit status is zero,  the  then
490              list  is  executed.   Otherwise,  each  elif list is executed in
491              turn, and if its exit status is  zero,  the  corresponding  then
492              list is executed and the command completes.  Otherwise, the else
493              list is executed, if present.  The exit status is the exit  sta‐
494              tus of the last command executed, or zero if no condition tested
495              true.
496
497       while list-1; do list-2; done
498       until list-1; do list-2; done
499              The while command continuously executes the list list-2 as  long
500              as the last command in the list list-1 returns an exit status of
501              zero.  The until command is  identical  to  the  while  command,
502              except  that  the test is negated: list-2 is executed as long as
503              the last command in list-1 returns a non-zero exit status.   The
504              exit  status  of the while and until commands is the exit status
505              of the last command executed in list-2, or zero if none was exe‐
506              cuted.
507
508   Coprocesses
509       A coprocess is a shell command preceded by the coproc reserved word.  A
510       coprocess is executed asynchronously in a subshell, as if  the  command
511       had  been  terminated  with the & control operator, with a two-way pipe
512       established between the executing shell and the coprocess.
513
514       The format for a coprocess is:
515
516              coproc [NAME] command [redirections]
517
518       This creates a coprocess named NAME.  If  NAME  is  not  supplied,  the
519       default name is COPROC.  NAME must not be supplied if command is a sim‐
520       ple command (see above); otherwise, it is interpreted as the first word
521       of  the simple command.  When the coprocess is executed, the shell cre‐
522       ates an array variable (see Arrays below) named NAME in the context  of
523       the executing shell.  The standard output of command is connected via a
524       pipe to a file  descriptor  in  the  executing  shell,  and  that  file
525       descriptor  is  assigned  to NAME[0].  The standard input of command is
526       connected via a pipe to a file descriptor in the executing  shell,  and
527       that  file descriptor is assigned to NAME[1].  This pipe is established
528       before any redirections  specified  by  the  command  (see  REDIRECTION
529       below).   The  file  descriptors  can be utilized as arguments to shell
530       commands and redirections using standard word expansions.   Other  than
531       those  created  to  execute command and process substitutions, the file
532       descriptors are not available in subshells.   The  process  ID  of  the
533       shell spawned to execute the coprocess is available as the value of the
534       variable NAME_PID.  The wait builtin command may be used  to  wait  for
535       the coprocess to terminate.
536
537       Since  the  coprocess is created as an asynchronous command, the coproc
538       command always returns success.  The return status of  a  coprocess  is
539       the exit status of command.
540
541   Shell Function Definitions
542       A  shell function is an object that is called like a simple command and
543       executes a compound command with a new set  of  positional  parameters.
544       Shell functions are declared as follows:
545
546       name () compound-command [redirection]
547       function name [()] compound-command [redirection]
548              This  defines a function named name.  The reserved word function
549              is optional.  If the function reserved  word  is  supplied,  the
550              parentheses  are optional.  The body of the function is the com‐
551              pound command compound-command (see  Compound  Commands  above).
552              That  command is usually a list of commands between { and }, but
553              may be any command listed under Compound  Commands  above,  with
554              one  exception:  If  the function reserved word is used, but the
555              parentheses are not supplied, the  braces  are  required.   com‐
556              pound-command is executed whenever name is specified as the name
557              of a simple command.  When in posix mode, name may  not  be  the
558              name  of  one  of  the POSIX special builtins.  Any redirections
559              (see REDIRECTION below) specified when a function is defined are
560              performed  when  the function is executed.  The exit status of a
561              function definition is zero unless a syntax error  occurs  or  a
562              readonly  function with the same name already exists.  When exe‐
563              cuted, the exit status of a function is the exit status  of  the
564              last command executed in the body.  (See FUNCTIONS below.)
565

COMMENTS

567       In a non-interactive shell, or an interactive shell in which the inter‐
568       active_comments option to the  shopt  builtin  is  enabled  (see  SHELL
569       BUILTIN  COMMANDS  below), a word beginning with # causes that word and
570       all remaining characters on that line to be  ignored.   An  interactive
571       shell  without  the  interactive_comments option enabled does not allow
572       comments.  The interactive_comments option is on by default in interac‐
573       tive shells.
574

QUOTING

576       Quoting  is used to remove the special meaning of certain characters or
577       words to the shell.  Quoting can be used to disable  special  treatment
578       for special characters, to prevent reserved words from being recognized
579       as such, and to prevent parameter expansion.
580
581       Each of the metacharacters listed above under DEFINITIONS  has  special
582       meaning to the shell and must be quoted if it is to represent itself.
583
584       When  the command history expansion facilities are being used (see HIS‐
585       TORY EXPANSION below), the history expansion character, usually !, must
586       be quoted to prevent history expansion.
587
588       There  are  three  quoting  mechanisms:  the  escape  character, single
589       quotes, and double quotes.
590
591       A non-quoted backslash (\) is the escape character.  It  preserves  the
592       literal value of the next character that follows, with the exception of
593       <newline>.  If a \<newline> pair appears,  and  the  backslash  is  not
594       itself  quoted,  the \<newline> is treated as a line continuation (that
595       is, it is removed from the input stream and effectively ignored).
596
597       Enclosing characters in single quotes preserves the  literal  value  of
598       each character within the quotes.  A single quote may not occur between
599       single quotes, even when preceded by a backslash.
600
601       Enclosing characters in double quotes preserves the  literal  value  of
602       all  characters  within the quotes, with the exception of $, `, \, and,
603       when history expansion is enabled, !.  When the shell is in posix mode,
604       the  !  has  no special meaning within double quotes, even when history
605       expansion is enabled.  The characters $  and  `  retain  their  special
606       meaning  within double quotes.  The backslash retains its special mean‐
607       ing only when followed by one of the following characters: $, `, ",  \,
608       or  <newline>.   A  double  quote may be quoted within double quotes by
609       preceding it with a backslash.  If enabled, history expansion  will  be
610       performed  unless  an  !  appearing in double quotes is escaped using a
611       backslash.  The backslash preceding the !  is not removed.
612
613       The special parameters * and @ have  special  meaning  when  in  double
614       quotes (see PARAMETERS below).
615
616       Words of the form $'string' are treated specially.  The word expands to
617       string, with backslash-escaped characters replaced as specified by  the
618       ANSI  C  standard.  Backslash escape sequences, if present, are decoded
619       as follows:
620              \a     alert (bell)
621              \b     backspace
622              \e
623              \E     an escape character
624              \f     form feed
625              \n     new line
626              \r     carriage return
627              \t     horizontal tab
628              \v     vertical tab
629              \\     backslash
630              \'     single quote
631              \"     double quote
632              \?     question mark
633              \nnn   the eight-bit character whose value is  the  octal  value
634                     nnn (one to three octal digits)
635              \xHH   the  eight-bit  character  whose value is the hexadecimal
636                     value HH (one or two hex digits)
637              \uHHHH the Unicode (ISO/IEC 10646) character whose value is  the
638                     hexadecimal value HHHH (one to four hex digits)
639              \UHHHHHHHH
640                     the  Unicode (ISO/IEC 10646) character whose value is the
641                     hexadecimal value HHHHHHHH (one to eight hex digits)
642              \cx    a control-x character
643
644       The expanded result is single-quoted, as if the  dollar  sign  had  not
645       been present.
646
647       A double-quoted string preceded by a dollar sign ($"string") will cause
648       the string to be translated according to the current  locale.   If  the
649       current  locale  is  C  or  POSIX,  the dollar sign is ignored.  If the
650       string is translated and replaced, the replacement is double-quoted.
651

PARAMETERS

653       A parameter is an entity that stores values.  It can be a name, a  num‐
654       ber, or one of the special characters listed below under Special Param‐
655       eters.  A variable is a parameter denoted by a name.  A variable has  a
656       value  and  zero or more attributes.  Attributes are assigned using the
657       declare builtin command (see declare below in SHELL BUILTIN COMMANDS).
658
659       A parameter is set if it has been assigned a value.  The null string is
660       a  valid  value.  Once a variable is set, it may be unset only by using
661       the unset builtin command (see SHELL BUILTIN COMMANDS below).
662
663       A variable may be assigned to by a statement of the form
664
665              name=[value]
666
667       If value is not given, the variable is assigned the null  string.   All
668       values  undergo tilde expansion, parameter and variable expansion, com‐
669       mand substitution, arithmetic expansion, and quote removal (see  EXPAN‐
670       SION below).  If the variable has its integer attribute set, then value
671       is evaluated as an arithmetic expression even if the $((...)) expansion
672       is  not  used  (see Arithmetic Expansion below).  Word splitting is not
673       performed, with the exception of "$@" as explained below under  Special
674       Parameters.   Pathname  expansion  is not performed.  Assignment state‐
675       ments may also appear as arguments  to  the  alias,  declare,  typeset,
676       export,  readonly,  and  local builtin commands (declaration commands).
677       When in posix mode, these builtins may appear in a command after one or
678       more  instances  of  the  command  builtin  and retain these assignment
679       statement properties.
680
681       In the context where an assignment statement is assigning a value to  a
682       shell variable or array index, the += operator can be used to append to
683       or add to the variable's previous value.  This  includes  arguments  to
684       builtin  commands  such  as  declare  that accept assignment statements
685       (declaration commands).  When += is applied to a variable for which the
686       integer  attribute  has  been  set, value is evaluated as an arithmetic
687       expression and added to the variable's current  value,  which  is  also
688       evaluated.   When  +=  is  applied  to an array variable using compound
689       assignment (see Arrays below), the variable's value is not unset (as it
690       is when using =), and new values are appended to the array beginning at
691       one greater than the array's maximum  index  (for  indexed  arrays)  or
692       added  as  additional  key-value  pairs  in an associative array.  When
693       applied to a string-valued variable, value is expanded and appended  to
694       the variable's value.
695
696       A variable can be assigned the nameref attribute using the -n option to
697       the declare or local builtin commands (see the descriptions of  declare
698       and  local  below) to create a nameref, or a reference to another vari‐
699       able.  This allows variables to be  manipulated  indirectly.   Whenever
700       the  nameref  variable  is  referenced,  assigned to, unset, or has its
701       attributes modified (other than using or changing the nameref attribute
702       itself),  the operation is actually performed on the variable specified
703       by the nameref variable's value.  A nameref  is  commonly  used  within
704       shell functions to refer to a variable whose name is passed as an argu‐
705       ment to the function.  For instance, if a variable name is passed to  a
706       shell function as its first argument, running
707              declare -n ref=$1
708       inside  the  function creates a nameref variable ref whose value is the
709       variable name passed as the first argument.  References and assignments
710       to  ref,  and  changes  to  its  attributes, are treated as references,
711       assignments, and attribute modifications to the variable whose name was
712       passed  as  $1.   If the control variable in a for loop has the nameref
713       attribute, the list of words can be a list of shell  variables,  and  a
714       name  reference will be established for each word in the list, in turn,
715       when the loop is executed.  Array variables cannot be given the nameref
716       attribute.   However,  nameref  variables can reference array variables
717       and subscripted array variables.  Namerefs can be unset  using  the  -n
718       option  to the unset builtin.  Otherwise, if unset is executed with the
719       name of a nameref variable as an argument, the variable  referenced  by
720       the nameref variable will be unset.
721
722   Positional Parameters
723       A  positional  parameter  is a parameter denoted by one or more digits,
724       other than the single digit 0.  Positional parameters are assigned from
725       the  shell's  arguments when it is invoked, and may be reassigned using
726       the set builtin command.  Positional parameters may not be assigned  to
727       with  assignment statements.  The positional parameters are temporarily
728       replaced when a shell function is executed (see FUNCTIONS below).
729
730       When a positional parameter consisting of more than a single  digit  is
731       expanded, it must be enclosed in braces (see EXPANSION below).
732
733   Special Parameters
734       The  shell  treats  several parameters specially.  These parameters may
735       only be referenced; assignment to them is not allowed.
736       *      Expands to the positional parameters, starting from  one.   When
737              the  expansion  is  not  within  double  quotes, each positional
738              parameter expands to a separate word.  In contexts where  it  is
739              performed, those words are subject to further word splitting and
740              pathname expansion.  When the  expansion  occurs  within  double
741              quotes,  it  expands  to  a  single  word with the value of each
742              parameter separated by the first character of  the  IFS  special
743              variable.   That  is, "$*" is equivalent to "$1c$2c...", where c
744              is the first character of the value of the IFS variable.  If IFS
745              is  unset,  the  parameters  are separated by spaces.  If IFS is
746              null, the parameters are joined without intervening separators.
747       @      Expands to the positional parameters,  starting  from  one.   In
748              contexts  where  word  splitting is performed, this expands each
749              positional parameter to a separate word; if  not  within  double
750              quotes,  these words are subject to word splitting.  In contexts
751              where word splitting is not performed, this expands to a  single
752              word  with each positional parameter separated by a space.  When
753              the  expansion  occurs  within  double  quotes,  each  parameter
754              expands to a separate word.  That is, "$@" is equivalent to "$1"
755              "$2" ...  If the double-quoted expansion occurs within  a  word,
756              the  expansion  of the first parameter is joined with the begin‐
757              ning part of the original word, and the expansion  of  the  last
758              parameter  is  joined  with  the last part of the original word.
759              When there are no positional parameters, "$@" and $@  expand  to
760              nothing (i.e., they are removed).
761       #      Expands to the number of positional parameters in decimal.
762       ?      Expands  to  the exit status of the most recently executed fore‐
763              ground pipeline.
764       -      Expands to the current option flags as  specified  upon  invoca‐
765              tion,  by  the  set  builtin  command, or those set by the shell
766              itself (such as the -i option).
767       $      Expands to the process ID of the shell.  In a  ()  subshell,  it
768              expands  to  the  process  ID of the current shell, not the sub‐
769              shell.
770       !      Expands to the process ID of the job most recently  placed  into
771              the  background,  whether executed as an asynchronous command or
772              using the bg builtin (see JOB CONTROL below).
773       0      Expands to the name of the shell or shell script.  This  is  set
774              at shell initialization.  If bash is invoked with a file of com‐
775              mands, $0 is set to the name of that file.  If bash  is  started
776              with  the  -c option, then $0 is set to the first argument after
777              the string to be executed, if one is present.  Otherwise, it  is
778              set  to  the  filename used to invoke bash, as given by argument
779              zero.
780       _      At shell startup, set to the absolute pathname  used  to  invoke
781              the  shell or shell script being executed as passed in the envi‐
782              ronment or argument list.  Subsequently,  expands  to  the  last
783              argument  to  the  previous simple command executed in the fore‐
784              ground, after expansion.  Also set to the full pathname used  to
785              invoke  each  command  executed  and  placed  in the environment
786              exported to that command.  When checking  mail,  this  parameter
787              holds the name of the mail file currently being checked.
788
789   Shell Variables
790       The following variables are set by the shell:
791
792       BASH   Expands  to  the  full  filename used to invoke this instance of
793              bash.
794       BASHOPTS
795              A colon-separated list of enabled shell options.  Each  word  in
796              the  list  is  a  valid  argument for the -s option to the shopt
797              builtin command (see SHELL BUILTIN COMMANDS below).  The options
798              appearing  in  BASHOPTS  are  those reported as on by shopt.  If
799              this variable is in the environment when bash  starts  up,  each
800              shell  option  in  the  list  will be enabled before reading any
801              startup files.  This variable is read-only.
802       BASHPID
803              Expands to the process ID of the  current  bash  process.   This
804              differs  from  $$ under certain circumstances, such as subshells
805              that do not require bash to be re-initialized.   Assignments  to
806              BASHPID  have no effect.  If BASHPID is unset, it loses its spe‐
807              cial properties, even if it is subsequently reset.
808       BASH_ALIASES
809              An associative array variable whose members  correspond  to  the
810              internal  list  of  aliases  as maintained by the alias builtin.
811              Elements added to this array appear in the alias list;  however,
812              unsetting  array elements currently does not cause aliases to be
813              removed from the alias list.  If BASH_ALIASES is unset, it loses
814              its special properties, even if it is subsequently reset.
815       BASH_ARGC
816              An  array  variable whose values are the number of parameters in
817              each frame of the current bash execution call stack.  The number
818              of  parameters  to  the  current  subroutine  (shell function or
819              script executed with . or source) is at the top  of  the  stack.
820              When  a  subroutine is executed, the number of parameters passed
821              is pushed onto BASH_ARGC.  The shell sets BASH_ARGC only when in
822              extended  debugging  mode  (see  the description of the extdebug
823              option to the shopt builtin below).  Setting extdebug after  the
824              shell has started to execute a script, or referencing this vari‐
825              able when extdebug is not set, may result in  inconsistent  val‐
826              ues.
827       BASH_ARGV
828              An  array  variable containing all of the parameters in the cur‐
829              rent bash execution call stack.  The final parameter of the last
830              subroutine  call is at the top of the stack; the first parameter
831              of the initial call is at the bottom.  When a subroutine is exe‐
832              cuted,  the  parameters supplied are pushed onto BASH_ARGV.  The
833              shell sets BASH_ARGV only when in extended debugging  mode  (see
834              the  description  of  the  extdebug  option to the shopt builtin
835              below).  Setting extdebug after the shell has started to execute
836              a script, or referencing this variable when extdebug is not set,
837              may result in inconsistent values.
838       BASH_ARGV0
839              When referenced, this variable expands to the name of the  shell
840              or shell script (identical to $0; see the description of special
841              parameter 0 above).  Assignment to BASH_ARGV0 causes  the  value
842              assigned  to also be assigned to $0.  If BASH_ARGV0 is unset, it
843              loses its special properties, even if it is subsequently reset.
844       BASH_CMDS
845              An associative array variable whose members  correspond  to  the
846              internal  hash  table  of  commands  as  maintained  by the hash
847              builtin.  Elements added to this array appear in the hash table;
848              however,  unsetting array elements currently does not cause com‐
849              mand names to be removed from the hash table.  If  BASH_CMDS  is
850              unset,  it  loses  its  special properties, even if it is subse‐
851              quently reset.
852       BASH_COMMAND
853              The command currently being executed or about  to  be  executed,
854              unless the shell is executing a command as the result of a trap,
855              in which case it is the command executing at  the  time  of  the
856              trap.
857       BASH_EXECUTION_STRING
858              The command argument to the -c invocation option.
859       BASH_LINENO
860              An  array  variable whose members are the line numbers in source
861              files where each corresponding member of FUNCNAME  was  invoked.
862              ${BASH_LINENO[$i]}  is  the  line  number  in  the  source  file
863              (${BASH_SOURCE[$i+1]})  where  ${FUNCNAME[$i]}  was  called  (or
864              ${BASH_LINENO[$i-1]}  if  referenced  within another shell func‐
865              tion).  Use LINENO to obtain the current line number.
866       BASH_LOADABLES_PATH
867              A colon-separated list of directories in which the  shell  looks
868              for  dynamically  loadable builtins specified by the enable com‐
869              mand.
870       BASH_REMATCH
871              An array variable whose members are assigned by  the  =~  binary
872              operator  to the [[ conditional command.  The element with index
873              0 is the portion of  the  string  matching  the  entire  regular
874              expression.   The  element  with  index  n is the portion of the
875              string matching the nth parenthesized subexpression.  This vari‐
876              able is read-only.
877       BASH_SOURCE
878              An  array  variable whose members are the source filenames where
879              the corresponding shell function names  in  the  FUNCNAME  array
880              variable  are  defined.   The  shell function ${FUNCNAME[$i]} is
881              defined  in  the  file  ${BASH_SOURCE[$i]}   and   called   from
882              ${BASH_SOURCE[$i+1]}.
883       BASH_SUBSHELL
884              Incremented  by one within each subshell or subshell environment
885              when the shell begins executing in that environment.   The  ini‐
886              tial value is 0.
887       BASH_VERSINFO
888              A readonly array variable whose members hold version information
889              for this instance of bash.  The values  assigned  to  the  array
890              members are as follows:
891              BASH_VERSINFO[0]        The major version number (the release).
892              BASH_VERSINFO[1]        The minor version number (the version).
893              BASH_VERSINFO[2]        The patch level.
894              BASH_VERSINFO[3]        The build version.
895              BASH_VERSINFO[4]        The release status (e.g., beta1).
896              BASH_VERSINFO[5]        The value of MACHTYPE.
897       BASH_VERSION
898              Expands  to  a string describing the version of this instance of
899              bash.
900       COMP_CWORD
901              An index into ${COMP_WORDS} of the word containing  the  current
902              cursor position.  This variable is available only in shell func‐
903              tions invoked by the  programmable  completion  facilities  (see
904              Programmable Completion below).
905       COMP_KEY
906              The key (or final key of a key sequence) used to invoke the cur‐
907              rent completion function.
908       COMP_LINE
909              The current command line.  This variable is  available  only  in
910              shell  functions  and  external commands invoked by the program‐
911              mable completion facilities (see Programmable Completion below).
912       COMP_POINT
913              The index of the current cursor position relative to the  begin‐
914              ning  of the current command.  If the current cursor position is
915              at the end of the current command, the value of this variable is
916              equal  to  ${#COMP_LINE}.   This  variable  is available only in
917              shell functions and external commands invoked  by  the  program‐
918              mable completion facilities (see Programmable Completion below).
919       COMP_TYPE
920              Set  to an integer value corresponding to the type of completion
921              attempted that caused a completion function to be  called:  TAB,
922              for  normal completion, ?, for listing completions after succes‐
923              sive tabs, !, for listing alternatives on partial  word  comple‐
924              tion,  @,  to list completions if the word is not unmodified, or
925              %, for menu completion.  This  variable  is  available  only  in
926              shell  functions  and  external commands invoked by the program‐
927              mable completion facilities (see Programmable Completion below).
928       COMP_WORDBREAKS
929              The set of characters that the readline library treats  as  word
930              separators  when performing word completion.  If COMP_WORDBREAKS
931              is unset, it loses its special properties, even if it is  subse‐
932              quently reset.
933       COMP_WORDS
934              An  array variable (see Arrays below) consisting of the individ‐
935              ual words in the current command line.  The line is  split  into
936              words  as  readline  would  split  it,  using COMP_WORDBREAKS as
937              described above.  This variable is available only in shell func‐
938              tions  invoked  by  the  programmable completion facilities (see
939              Programmable Completion below).
940       COPROC An array variable (see Arrays below) created to  hold  the  file
941              descriptors  for  output  from and input to an unnamed coprocess
942              (see Coprocesses above).
943       DIRSTACK
944              An array variable (see Arrays below) containing the current con‐
945              tents  of  the directory stack.  Directories appear in the stack
946              in the order they are displayed by the dirs builtin.   Assigning
947              to members of this array variable may be used to modify directo‐
948              ries already in the stack, but the pushd and popd builtins  must
949              be used to add and remove directories.  Assignment to this vari‐
950              able will not change the  current  directory.   If  DIRSTACK  is
951              unset,  it  loses  its  special properties, even if it is subse‐
952              quently reset.
953       EPOCHREALTIME
954              Each time this parameter is referenced, it expands to the number
955              of  seconds  since  the  Unix  Epoch (see time(3)) as a floating
956              point  value  with  micro-second  granularity.   Assignments  to
957              EPOCHREALTIME  are ignored.  If EPOCHREALTIME is unset, it loses
958              its special properties, even if it is subsequently reset.
959       EPOCHSECONDS
960              Each time this parameter is referenced, it expands to the number
961              of  seconds  since the Unix Epoch (see time(3)).  Assignments to
962              EPOCHSECONDS are ignored.  If EPOCHSECONDS is  unset,  it  loses
963              its special properties, even if it is subsequently reset.
964       EUID   Expands  to  the effective user ID of the current user, initial‐
965              ized at shell startup.  This variable is readonly.
966       FUNCNAME
967              An array variable containing the names of  all  shell  functions
968              currently in the execution call stack.  The element with index 0
969              is the name of any currently-executing shell function.  The bot‐
970              tom-most  element  (the  one  with the highest index) is "main".
971              This variable exists only when a shell  function  is  executing.
972              Assignments  to  FUNCNAME have no effect.  If FUNCNAME is unset,
973              it loses its special properties,  even  if  it  is  subsequently
974              reset.
975
976              This  variable  can  be  used  with BASH_LINENO and BASH_SOURCE.
977              Each  element  of  FUNCNAME  has   corresponding   elements   in
978              BASH_LINENO  and  BASH_SOURCE  to  describe the call stack.  For
979              instance,   ${FUNCNAME[$i]}   was   called   from    the    file
980              ${BASH_SOURCE[$i+1]}  at  line  number  ${BASH_LINENO[$i]}.  The
981              caller builtin displays the current call stack using this infor‐
982              mation.
983       GROUPS An  array  variable  containing  the list of groups of which the
984              current user is a member.  Assignments to GROUPS have no effect.
985              If  GROUPS is unset, it loses its special properties, even if it
986              is subsequently reset.
987       HISTCMD
988              The history number, or index in the history list, of the current
989              command.   If HISTCMD is unset, it loses its special properties,
990              even if it is subsequently reset.
991       HOSTNAME
992              Automatically set to the name of the current host.
993       HOSTTYPE
994              Automatically set to a string that uniquely describes  the  type
995              of  machine  on which bash is executing.  The default is system-
996              dependent.
997       LINENO Each time this parameter is referenced, the shell substitutes  a
998              decimal  number  representing the current sequential line number
999              (starting with 1) within a script or function.  When  not  in  a
1000              script  or  function, the value substituted is not guaranteed to
1001              be meaningful.  If LINENO is unset, it loses its special proper‐
1002              ties, even if it is subsequently reset.
1003       MACHTYPE
1004              Automatically  set  to  a string that fully describes the system
1005              type on which bash is executing, in the  standard  GNU  cpu-com‐
1006              pany-system format.  The default is system-dependent.
1007       MAPFILE
1008              An  array  variable  (see Arrays below) created to hold the text
1009              read by the mapfile builtin when no variable name is supplied.
1010       OLDPWD The previous working directory as set by the cd command.
1011       OPTARG The value of the last option argument processed by  the  getopts
1012              builtin command (see SHELL BUILTIN COMMANDS below).
1013       OPTIND The  index  of  the next argument to be processed by the getopts
1014              builtin command (see SHELL BUILTIN COMMANDS below).
1015       OSTYPE Automatically set to a string that describes the operating  sys‐
1016              tem  on  which  bash is executing.  The default is system-depen‐
1017              dent.
1018       PIPESTATUS
1019              An array variable (see Arrays below) containing a list  of  exit
1020              status  values  from the processes in the most-recently-executed
1021              foreground pipeline (which may contain only a single command).
1022       PPID   The process ID of the shell's parent.  This  variable  is  read‐
1023              only.
1024       PWD    The current working directory as set by the cd command.
1025       RANDOM Each time this parameter is referenced, a random integer between
1026              0 and 32767 is generated.  The sequence of random numbers may be
1027              initialized by assigning a value to RANDOM.  If RANDOM is unset,
1028              it loses its special properties,  even  if  it  is  subsequently
1029              reset.
1030       READLINE_LINE
1031              The contents of the readline line buffer, for use with "bind -x"
1032              (see SHELL BUILTIN COMMANDS below).
1033       READLINE_POINT
1034              The position of the insertion point in the readline line buffer,
1035              for use with "bind -x" (see SHELL BUILTIN COMMANDS below).
1036       REPLY  Set  to  the line of input read by the read builtin command when
1037              no arguments are supplied.
1038       SECONDS
1039              Each time this parameter is referenced, the  number  of  seconds
1040              since  shell  invocation is returned.  If a value is assigned to
1041              SECONDS, the value returned upon subsequent  references  is  the
1042              number  of seconds since the assignment plus the value assigned.
1043              If SECONDS is unset, it loses its special properties, even if it
1044              is subsequently reset.
1045       SHELLOPTS
1046              A  colon-separated  list of enabled shell options.  Each word in
1047              the list is a valid argument  for  the  -o  option  to  the  set
1048              builtin command (see SHELL BUILTIN COMMANDS below).  The options
1049              appearing in SHELLOPTS are those reported as on by set  -o.   If
1050              this  variable  is  in the environment when bash starts up, each
1051              shell option in the list will  be  enabled  before  reading  any
1052              startup files.  This variable is read-only.
1053       SHLVL  Incremented by one each time an instance of bash is started.
1054       UID    Expands to the user ID of the current user, initialized at shell
1055              startup.  This variable is readonly.
1056
1057       The following variables are used by the shell.   In  some  cases,  bash
1058       assigns a default value to a variable; these cases are noted below.
1059
1060       BASH_COMPAT
1061              The  value  is used to set the shell's compatibility level.  See
1062              the description of the shopt builtin below under  SHELL  BUILTIN
1063              COMMANDS  for  a description of the various compatibility levels
1064              and their effects.  The value may be  a  decimal  number  (e.g.,
1065              4.2)  or an integer (e.g., 42) corresponding to the desired com‐
1066              patibility level.  If BASH_COMPAT is unset or set to  the  empty
1067              string,  the  compatibility  level is set to the default for the
1068              current version.  If BASH_COMPAT is set to a value that  is  not
1069              one of the valid compatibility levels, the shell prints an error
1070              message and sets the compatibility level to the default for  the
1071              current  version.   The valid compatibility levels correspond to
1072              the  compatibility  options  accepted  by  the   shopt   builtin
1073              described below (for example, compat42 means that 4.2 and 42 are
1074              valid values).  The current version is also a valid value.
1075       BASH_ENV
1076              If this parameter is set when bash is executing a shell  script,
1077              its  value  is  interpreted as a filename containing commands to
1078              initialize the shell, as in ~/.bashrc.  The value of BASH_ENV is
1079              subjected  to  parameter  expansion,  command  substitution, and
1080              arithmetic expansion before being  interpreted  as  a  filename.
1081              PATH is not used to search for the resultant filename.
1082       BASH_XTRACEFD
1083              If  set  to an integer corresponding to a valid file descriptor,
1084              bash will write the  trace  output  generated  when  set  -x  is
1085              enabled  to that file descriptor.  The file descriptor is closed
1086              when BASH_XTRACEFD is unset or assigned a new value.   Unsetting
1087              BASH_XTRACEFD  or assigning it the empty string causes the trace
1088              output to be sent to the  standard  error.   Note  that  setting
1089              BASH_XTRACEFD to 2 (the standard error file descriptor) and then
1090              unsetting it will result in the standard error being closed.
1091       CDPATH The search path for the cd command.  This is  a  colon-separated
1092              list  of  directories  in  which the shell looks for destination
1093              directories specified by the cd  command.   A  sample  value  is
1094              ".:~:/usr".
1095       CHILD_MAX
1096              Set  the  number  of exited child status values for the shell to
1097              remember.  Bash will not allow this value to be decreased  below
1098              a  POSIX-mandated  minimum,  and  there is a maximum value (cur‐
1099              rently 8192) that this may not exceed.   The  minimum  value  is
1100              system-dependent.
1101       COLUMNS
1102              Used  by  the  select compound command to determine the terminal
1103              width when printing selection lists.  Automatically set  if  the
1104              checkwinsize  option  is enabled or in an interactive shell upon
1105              receipt of a SIGWINCH.
1106       COMPREPLY
1107              An array variable from which bash reads the possible completions
1108              generated  by  a shell function invoked by the programmable com‐
1109              pletion facility  (see  Programmable  Completion  below).   Each
1110              array element contains one possible completion.
1111       EMACS  If  bash  finds  this variable in the environment when the shell
1112              starts with value "t", it assumes that the shell is  running  in
1113              an Emacs shell buffer and disables line editing.
1114       ENV    Similar  to  BASH_ENV;  used  when the shell is invoked in posix
1115              mode.
1116       EXECIGNORE
1117              A colon-separated list of shell patterns (see Pattern  Matching)
1118              defining  the  list of filenames to be ignored by command search
1119              using PATH.  Files whose full pathnames match one of these  pat‐
1120              terns  are  not  considered executable files for the purposes of
1121              completion and command execution via PATH lookup.  This does not
1122              affect the behavior of the [, test, and [[ commands.  Full path‐
1123              names in the command hash table are not subject  to  EXECIGNORE.
1124              Use  this  variable to ignore shared library files that have the
1125              executable bit set, but are not executable files.   The  pattern
1126              matching honors the setting of the extglob shell option.
1127       FCEDIT The default editor for the fc builtin command.
1128       FIGNORE
1129              A  colon-separated  list  of  suffixes to ignore when performing
1130              filename completion (see READLINE below).  A filename whose suf‐
1131              fix  matches  one of the entries in FIGNORE is excluded from the
1132              list of matched filenames.  A sample value is ".o:~".
1133       FUNCNEST
1134              If set to a numeric value greater  than  0,  defines  a  maximum
1135              function  nesting  level.  Function invocations that exceed this
1136              nesting level will cause the current command to abort.
1137       GLOBIGNORE
1138              A colon-separated list of patterns  defining  the  set  of  file
1139              names  to  be  ignored  by  pathname  expansion.  If a file name
1140              matched by a pathname expansion pattern also matches one of  the
1141              patterns in GLOBIGNORE, it is removed from the list of matches.
1142       HISTCONTROL
1143              A  colon-separated  list  of values controlling how commands are
1144              saved on the history list.   If  the  list  of  values  includes
1145              ignorespace,  lines  which  begin with a space character are not
1146              saved in the history list.  A value of ignoredups  causes  lines
1147              matching the previous history entry to not be saved.  A value of
1148              ignoreboth is shorthand for ignorespace and ignoredups.  A value
1149              of erasedups causes all previous lines matching the current line
1150              to be removed from the history list before that line  is  saved.
1151              Any  value  not in the above list is ignored.  If HISTCONTROL is
1152              unset, or does not include a valid value, all lines read by  the
1153              shell parser are saved on the history list, subject to the value
1154              of HISTIGNORE.  The second and subsequent lines of a  multi-line
1155              compound  command  are  not tested, and are added to the history
1156              regardless of the value of HISTCONTROL.
1157       HISTFILE
1158              The name of the file in which command history is saved (see HIS‐
1159              TORY  below).   The default value is ~/.bash_history.  If unset,
1160              the command history is not saved when a shell exits.
1161       HISTFILESIZE
1162              The maximum number of lines contained in the history file.  When
1163              this  variable  is  assigned  a value, the history file is trun‐
1164              cated, if necessary, to contain no  more  than  that  number  of
1165              lines  by removing the oldest entries.  The history file is also
1166              truncated to this size after writing it when a shell exits.   If
1167              the  value  is  0,  the  history file is truncated to zero size.
1168              Non-numeric values and numeric values  less  than  zero  inhibit
1169              truncation.   The  shell  sets the default value to the value of
1170              HISTSIZE after reading any startup files.
1171       HISTIGNORE
1172              A colon-separated list of patterns used to decide which  command
1173              lines  should  be  saved  on  the history list.  Each pattern is
1174              anchored at the beginning of the line and must  match  the  com‐
1175              plete  line  (no  implicit  `*'  is  appended).  Each pattern is
1176              tested against the line after the checks specified  by  HISTCON‐
1177              TROL  are  applied.   In  addition  to  the normal shell pattern
1178              matching characters, `&' matches the previous history line.  `&'
1179              may  be  escaped  using  a  backslash;  the backslash is removed
1180              before attempting a match.  The second and subsequent lines of a
1181              multi-line compound command are not tested, and are added to the
1182              history regardless of the  value  of  HISTIGNORE.   The  pattern
1183              matching honors the setting of the extglob shell option.
1184       HISTSIZE
1185              The  number  of commands to remember in the command history (see
1186              HISTORY below).  If the value is 0, commands are  not  saved  in
1187              the history list.  Numeric values less than zero result in every
1188              command being saved on the history list  (there  is  no  limit).
1189              The  shell  sets  the  default  value  to  500 after reading any
1190              startup files.
1191       HISTTIMEFORMAT
1192              If this variable is set and not null, its value  is  used  as  a
1193              format string for strftime(3) to print the time stamp associated
1194              with each history entry displayed by the  history  builtin.   If
1195              this  variable  is  set,  time stamps are written to the history
1196              file so they may be preserved across shell sessions.  This  uses
1197              the  history  comment  character  to distinguish timestamps from
1198              other history lines.
1199       HOME   The home directory of the current user; the default argument for
1200              the cd builtin command.  The value of this variable is also used
1201              when performing tilde expansion.
1202       HOSTFILE
1203              Contains the name of a file in the  same  format  as  /etc/hosts
1204              that should be read when the shell needs to complete a hostname.
1205              The list of possible hostname completions may be  changed  while
1206              the  shell  is  running;  the  next  time hostname completion is
1207              attempted after the value is changed, bash adds the contents  of
1208              the  new file to the existing list.  If HOSTFILE is set, but has
1209              no value, or does not name a readable  file,  bash  attempts  to
1210              read  /etc/hosts to obtain the list of possible hostname comple‐
1211              tions.  When HOSTFILE is unset, the hostname list is cleared.
1212       IFS    The Internal Field Separator that is  used  for  word  splitting
1213              after  expansion  and  to  split  lines into words with the read
1214              builtin  command.   The  default  value  is  ``<space><tab><new‐
1215              line>''.
1216       IGNOREEOF
1217              Controls the action of an interactive shell on receipt of an EOF
1218              character as the sole input.  If set, the value is the number of
1219              consecutive  EOF  characters  which  must  be typed as the first
1220              characters on an input line before bash exits.  If the  variable
1221              exists  but  does not have a numeric value, or has no value, the
1222              default value is 10.  If it does not exist,  EOF  signifies  the
1223              end of input to the shell.
1224       INPUTRC
1225              The  filename  for  the  readline  startup  file, overriding the
1226              default of ~/.inputrc (see READLINE below).
1227       INSIDE_EMACS
1228              If this variable appears  in  the  environment  when  the  shell
1229              starts,  bash  assumes  that it is running inside an Emacs shell
1230              buffer and may disable line editing, depending on the  value  of
1231              TERM.
1232       LANG   Used  to  determine  the  locale  category  for any category not
1233              specifically selected with a variable starting with LC_.
1234       LC_ALL This variable overrides the value of  LANG  and  any  other  LC_
1235              variable specifying a locale category.
1236       LC_COLLATE
1237              This  variable  determines the collation order used when sorting
1238              the results of pathname expansion, and determines  the  behavior
1239              of   range   expressions,  equivalence  classes,  and  collating
1240              sequences within pathname expansion and pattern matching.
1241       LC_CTYPE
1242              This variable determines the interpretation  of  characters  and
1243              the  behavior of character classes within pathname expansion and
1244              pattern matching.
1245       LC_MESSAGES
1246              This variable determines the locale used  to  translate  double-
1247              quoted strings preceded by a $.
1248       LC_NUMERIC
1249              This  variable  determines  the  locale category used for number
1250              formatting.
1251       LC_TIME
1252              This variable determines the locale category used for  data  and
1253              time formatting.
1254       LINES  Used  by  the  select  compound  command to determine the column
1255              length for printing selection lists.  Automatically set  if  the
1256              checkwinsize  option  is enabled or in an interactive shell upon
1257              receipt of a SIGWINCH.
1258       MAIL   If this parameter is set to a file or  directory  name  and  the
1259              MAILPATH  variable  is  not  set,  bash  informs the user of the
1260              arrival of mail in the specified file or  Maildir-format  direc‐
1261              tory.
1262       MAILCHECK
1263              Specifies  how  often  (in  seconds)  bash checks for mail.  The
1264              default is 60 seconds.  When it is time to check for  mail,  the
1265              shell  does  so  before  displaying the primary prompt.  If this
1266              variable is unset, or set to  a  value  that  is  not  a  number
1267              greater than or equal to zero, the shell disables mail checking.
1268       MAILPATH
1269              A colon-separated list of filenames to be checked for mail.  The
1270              message to be printed when mail arrives in a particular file may
1271              be  specified by separating the filename from the message with a
1272              `?'.  When used in the text of the message, $_  expands  to  the
1273              name of the current mailfile.  Example:
1274              MAILPATH='/var/mail/bfox?"You  have  mail":~/shell-mail?"$_  has
1275              mail!"'
1276              Bash can be configured to supply a default value for this  vari‐
1277              able  (there  is  no  value by default), but the location of the
1278              user  mail  files  that  it  uses  is  system  dependent  (e.g.,
1279              /var/mail/$USER).
1280       OPTERR If set to the value 1, bash displays error messages generated by
1281              the getopts builtin command (see SHELL BUILTIN COMMANDS  below).
1282              OPTERR  is  initialized to 1 each time the shell is invoked or a
1283              shell script is executed.
1284       PATH   The search path for commands.  It is a colon-separated  list  of
1285              directories  in  which the shell looks for commands (see COMMAND
1286              EXECUTION below).  A zero-length (null) directory  name  in  the
1287              value of PATH indicates the current directory.  A null directory
1288              name may appear as two adjacent colons,  or  as  an  initial  or
1289              trailing  colon.   The  default path is system-dependent, and is
1290              set by the administrator who installs bash.  A common value is
1291              ``/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin''.
1292       POSIXLY_CORRECT
1293              If this variable is in the environment  when  bash  starts,  the
1294              shell  enters posix mode before reading the startup files, as if
1295              the --posix invocation option had been supplied.  If it  is  set
1296              while  the  shell is running, bash enables posix mode, as if the
1297              command set -o posix had been executed.  When the  shell  enters
1298              posix mode, it sets this variable if it was not already set.
1299       PROMPT_COMMAND
1300              If set, the value is executed as a command prior to issuing each
1301              primary prompt.
1302       PROMPT_DIRTRIM
1303              If set to a number greater than zero, the value is used  as  the
1304              number of trailing directory components to retain when expanding
1305              the \w and \W  prompt  string  escapes  (see  PROMPTING  below).
1306              Characters removed are replaced with an ellipsis.
1307       PS0    The  value  of  this parameter is expanded (see PROMPTING below)
1308              and displayed by interactive shells after reading a command  and
1309              before the command is executed.
1310       PS1    The  value  of  this parameter is expanded (see PROMPTING below)
1311              and used as the primary prompt string.   The  default  value  is
1312              ``\s-\v\$ ''.
1313       PS2    The  value of this parameter is expanded as with PS1 and used as
1314              the secondary prompt string.  The default is ``> ''.
1315       PS3    The value of this parameter is used as the prompt for the select
1316              command (see SHELL GRAMMAR above).
1317       PS4    The  value  of  this  parameter  is expanded as with PS1 and the
1318              value is printed before each command  bash  displays  during  an
1319              execution  trace.   The first character of the expanded value of
1320              PS4 is replicated multiple times, as necessary, to indicate mul‐
1321              tiple levels of indirection.  The default is ``+ ''.
1322       SHELL  The full pathname to the shell is kept in this environment vari‐
1323              able.  If it is not set when the shell starts, bash  assigns  to
1324              it the full pathname of the current user's login shell.
1325       TIMEFORMAT
1326              The  value of this parameter is used as a format string specify‐
1327              ing how the timing information for pipelines prefixed  with  the
1328              time  reserved word should be displayed.  The % character intro‐
1329              duces an escape sequence that is expanded to  a  time  value  or
1330              other  information.  The escape sequences and their meanings are
1331              as follows; the braces denote optional portions.
1332              %%        A literal %.
1333              %[p][l]R  The elapsed time in seconds.
1334              %[p][l]U  The number of CPU seconds spent in user mode.
1335              %[p][l]S  The number of CPU seconds spent in system mode.
1336              %P        The CPU percentage, computed as (%U + %S) / %R.
1337
1338              The optional p is a digit specifying the precision,  the  number
1339              of fractional digits after a decimal point.  A value of 0 causes
1340              no decimal point or fraction to be output.  At most three places
1341              after  the  decimal  point may be specified; values of p greater
1342              than 3 are changed to 3.  If p is not specified, the value 3  is
1343              used.
1344
1345              The  optional l specifies a longer format, including minutes, of
1346              the form MMmSS.FFs.  The value of p determines  whether  or  not
1347              the fraction is included.
1348
1349              If  this  variable  is not set, bash acts as if it had the value
1350              $'\nreal\t%3lR\nuser\t%3lU\nsys\t%3lS'.  If the value  is  null,
1351              no timing information is displayed.  A trailing newline is added
1352              when the format string is displayed.
1353       TMOUT  If set to a value greater than zero, TMOUT  is  treated  as  the
1354              default timeout for the read builtin.  The select command termi‐
1355              nates if input does not arrive after TMOUT seconds when input is
1356              coming  from  a terminal.  In an interactive shell, the value is
1357              interpreted as the number of seconds to wait for a line of input
1358              after issuing the primary prompt.  Bash terminates after waiting
1359              for that number of seconds if a complete line of input does  not
1360              arrive.
1361       TMPDIR If  set, bash uses its value as the name of a directory in which
1362              bash creates temporary files for the shell's use.
1363       auto_resume
1364              This variable controls how the shell interacts with the user and
1365              job  control.   If this variable is set, single word simple com‐
1366              mands without redirections are treated as candidates for resump‐
1367              tion of an existing stopped job.  There is no ambiguity allowed;
1368              if there is more than one job beginning with the  string  typed,
1369              the  job  most  recently  accessed  is  selected.  The name of a
1370              stopped job, in this context, is the command line used to  start
1371              it.   If  set to the value exact, the string supplied must match
1372              the name of a stopped job exactly;  if  set  to  substring,  the
1373              string  supplied  needs  to  match  a substring of the name of a
1374              stopped job.  The substring value provides functionality  analo‐
1375              gous  to the %?  job identifier (see JOB CONTROL below).  If set
1376              to any other value, the supplied string must be a  prefix  of  a
1377              stopped job's name; this provides functionality analogous to the
1378              %string job identifier.
1379       histchars
1380              The two or three characters which control history expansion  and
1381              tokenization (see HISTORY EXPANSION below).  The first character
1382              is the history expansion character, the character which  signals
1383              the  start  of  a  history  expansion, normally `!'.  The second
1384              character is the quick substitution character, which is used  as
1385              shorthand  for  re-running the previous command entered, substi‐
1386              tuting one string for another in the command.   The  default  is
1387              `^'.   The optional third character is the character which indi‐
1388              cates that the remainder of the line is a comment when found  as
1389              the  first  character of a word, normally `#'.  The history com‐
1390              ment character causes history substitution to be skipped for the
1391              remaining  words on the line.  It does not necessarily cause the
1392              shell parser to treat the rest of the line as a comment.
1393
1394   Arrays
1395       Bash provides one-dimensional indexed and associative array  variables.
1396       Any  variable may be used as an indexed array; the declare builtin will
1397       explicitly declare an array.  There is no maximum limit on the size  of
1398       an  array, nor any requirement that members be indexed or assigned con‐
1399       tiguously.  Indexed arrays are  referenced  using  integers  (including
1400       arithmetic expressions) and are zero-based; associative arrays are ref‐
1401       erenced using arbitrary strings.  Unless otherwise noted, indexed array
1402       indices must be non-negative integers.
1403
1404       An  indexed  array is created automatically if any variable is assigned
1405       to using the syntax name[subscript]=value.  The subscript is treated as
1406       an arithmetic expression that must evaluate to a number.  To explicitly
1407       declare an indexed array, use declare -a name (see SHELL  BUILTIN  COM‐
1408       MANDS  below).   declare  -a name[subscript] is also accepted; the sub‐
1409       script is ignored.
1410
1411       Associative arrays are created using declare -A name.
1412
1413       Attributes may be specified for an array variable using the declare and
1414       readonly builtins.  Each attribute applies to all members of an array.
1415
1416       Arrays   are  assigned  to  using  compound  assignments  of  the  form
1417       name=(value1 ... valuen),  where  each  value  is  of  the  form  [sub‐
1418       script]=string.   Indexed array assignments do not require anything but
1419       string.  When assigning to indexed arrays, if the optional brackets and
1420       subscript  are supplied, that index is assigned to; otherwise the index
1421       of the element assigned is the last index assigned to by the  statement
1422       plus one.  Indexing starts at zero.
1423
1424       When assigning to an associative array, the subscript is required.
1425
1426       This  syntax is also accepted by the declare builtin.  Individual array
1427       elements may be assigned  to  using  the  name[subscript]=value  syntax
1428       introduced  above.  When assigning to an indexed array, if name is sub‐
1429       scripted by a negative number, that number is interpreted  as  relative
1430       to  one  greater  than  the  maximum index of name, so negative indices
1431       count back from the end of the array, and an index of -1 references the
1432       last element.
1433
1434       Any  element  of  an  array may be referenced using ${name[subscript]}.
1435       The braces are required to avoid conflicts with pathname expansion.  If
1436       subscript  is  @  or *, the word expands to all members of name.  These
1437       subscripts differ only when the word appears within double quotes.   If
1438       the word is double-quoted, ${name[*]} expands to a single word with the
1439       value of each array member separated by the first character of the  IFS
1440       special variable, and ${name[@]} expands each element of name to a sep‐
1441       arate word.  When there are no array  members,  ${name[@]}  expands  to
1442       nothing.   If  the  double-quoted  expansion  occurs within a word, the
1443       expansion of the first parameter is joined with the beginning  part  of
1444       the  original  word,  and the expansion of the last parameter is joined
1445       with the last part of the original word.   This  is  analogous  to  the
1446       expansion  of  the  special  parameters * and @ (see Special Parameters
1447       above).  ${#name[subscript]}  expands  to  the  length  of  ${name[sub‐
1448       script]}.   If subscript is * or @, the expansion is the number of ele‐
1449       ments in the array.  If the subscript used to reference an  element  of
1450       an  indexed  array  evaluates  to a number less than zero, it is inter‐
1451       preted as relative to one greater than the maximum index of the  array,
1452       so  negative indices count back from the end of the array, and an index
1453       of -1 references the last element.
1454
1455       Referencing an array variable without a subscript is equivalent to ref‐
1456       erencing  the array with a subscript of 0.  Any reference to a variable
1457       using a valid subscript is legal, and bash will create an array if nec‐
1458       essary.
1459
1460       An  array variable is considered set if a subscript has been assigned a
1461       value.  The null string is a valid value.
1462
1463       It is possible to obtain the keys (indices) of an array as well as  the
1464       values.   ${!name[@]} and ${!name[*]} expand to the indices assigned in
1465       array variable name.  The treatment when in double quotes is similar to
1466       the expansion of the special parameters @ and * within double quotes.
1467
1468       The  unset  builtin  is  used to destroy arrays.  unset name[subscript]
1469       destroys the array element at index subscript,  for  both  indexed  and
1470       associative  arrays.   Negative subscripts to indexed arrays are inter‐
1471       preted as described above.  Unsetting the  last  element  of  an  array
1472       variable  does  not  unset  the variable.  unset name, where name is an
1473       array, or unset name[subscript], where subscript is * or @, removes the
1474       entire array.
1475
1476       When  using  a  variable name with a subscript as an argument to a com‐
1477       mand, such as with unset,  without  using  the  word  expansion  syntax
1478       described  above,  the  argument  is subject to pathname expansion.  If
1479       pathname expansion is not desired, the argument should be quoted.
1480
1481       The declare, local, and readonly builtins each accept a  -a  option  to
1482       specify  an  indexed  array  and  a -A option to specify an associative
1483       array.  If both options are supplied, -A takes  precedence.   The  read
1484       builtin  accepts  a  -a  option to assign a list of words read from the
1485       standard input to an array.  The set and declare builtins display array
1486       values in a way that allows them to be reused as assignments.
1487

EXPANSION

1489       Expansion is performed on the command line after it has been split into
1490       words.  There are seven kinds of expansion performed: brace  expansion,
1491       tilde  expansion,  parameter  and variable expansion, command substitu‐
1492       tion, arithmetic expansion, word splitting, and pathname expansion.
1493
1494       The order of expansions is: brace expansion; tilde expansion, parameter
1495       and  variable expansion, arithmetic expansion, and command substitution
1496       (done in a left-to-right fashion); word splitting; and pathname  expan‐
1497       sion.
1498
1499       On systems that can support it, there is an additional expansion avail‐
1500       able: process substitution.  This is performed  at  the  same  time  as
1501       tilde,  parameter,  variable, and arithmetic expansion and command sub‐
1502       stitution.
1503
1504       After these expansions are performed, quote characters present  in  the
1505       original  word  are  removed  unless  they  have been quoted themselves
1506       (quote removal).
1507
1508       Only brace  expansion,  word  splitting,  and  pathname  expansion  can
1509       increase  the number of words of the expansion; other expansions expand
1510       a single word to a single word.  The only exceptions to  this  are  the
1511       expansions  of  "$@"  and  "${name[@]}",  and,  in  most  cases, $* and
1512       ${name[*]} as explained above (see PARAMETERS).
1513
1514   Brace Expansion
1515       Brace expansion is a mechanism by which arbitrary strings may be gener‐
1516       ated.   This  mechanism is similar to pathname expansion, but the file‐
1517       names generated need not exist.  Patterns to be brace expanded take the
1518       form of an optional preamble, followed by either a series of comma-sep‐
1519       arated strings or a sequence expression between a pair of braces,  fol‐
1520       lowed  by  an  optional  postscript.   The preamble is prefixed to each
1521       string contained within the braces, and the postscript is then appended
1522       to each resulting string, expanding left to right.
1523
1524       Brace  expansions  may  be nested.  The results of each expanded string
1525       are not sorted;  left  to  right  order  is  preserved.   For  example,
1526       a{d,c,b}e expands into `ade ace abe'.
1527
1528       A  sequence expression takes the form {x..y[..incr]}, where x and y are
1529       either integers or single characters, and incr, an optional  increment,
1530       is  an  integer.  When integers are supplied, the expression expands to
1531       each number between x and y, inclusive.  Supplied integers may be  pre‐
1532       fixed  with 0 to force each term to have the same width.  When either x
1533       or y begins with a zero, the shell  attempts  to  force  all  generated
1534       terms  to  contain the same number of digits, zero-padding where neces‐
1535       sary.  When characters are supplied, the  expression  expands  to  each
1536       character  lexicographically  between  x  and  y,  inclusive, using the
1537       default C locale.  Note that both x and y must be  of  the  same  type.
1538       When  the  increment  is supplied, it is used as the difference between
1539       each term.  The default increment is 1 or -1 as appropriate.
1540
1541       Brace expansion is performed before any other expansions, and any char‐
1542       acters  special to other expansions are preserved in the result.  It is
1543       strictly textual.  Bash does not apply any syntactic interpretation  to
1544       the context of the expansion or the text between the braces.
1545
1546       A  correctly-formed  brace  expansion must contain unquoted opening and
1547       closing braces, and at least one unquoted comma  or  a  valid  sequence
1548       expression.   Any incorrectly formed brace expansion is left unchanged.
1549       A { or , may be quoted with a backslash to prevent its being considered
1550       part  of  a brace expression.  To avoid conflicts with parameter expan‐
1551       sion, the string ${ is not considered eligible for brace expansion, and
1552       inhibits brace expansion until the closing }.
1553
1554       This construct is typically used as shorthand when the common prefix of
1555       the strings to be generated is longer than in the above example:
1556
1557              mkdir /usr/local/src/bash/{old,new,dist,bugs}
1558       or
1559              chown root /usr/{ucb/{ex,edit},lib/{ex?.?*,how_ex}}
1560
1561       Brace expansion introduces a  slight  incompatibility  with  historical
1562       versions  of sh.  sh does not treat opening or closing braces specially
1563       when they appear as part of a word, and preserves them in  the  output.
1564       Bash  removes  braces  from  words as a consequence of brace expansion.
1565       For example, a word entered to sh as file{1,2} appears  identically  in
1566       the  output.  The same word is output as file1 file2 after expansion by
1567       bash.  If strict compatibility with sh is desired, start bash with  the
1568       +B option or disable brace expansion with the +B option to the set com‐
1569       mand (see SHELL BUILTIN COMMANDS below).
1570
1571   Tilde Expansion
1572       If a word begins with an unquoted tilde character  (`~'),  all  of  the
1573       characters  preceding  the  first unquoted slash (or all characters, if
1574       there is no unquoted slash) are considered a tilde-prefix.  If none  of
1575       the  characters  in  the tilde-prefix are quoted, the characters in the
1576       tilde-prefix following the tilde are treated as a possible login  name.
1577       If  this  login name is the null string, the tilde is replaced with the
1578       value of the shell parameter HOME.  If HOME is unset, the  home  direc‐
1579       tory  of  the  user executing the shell is substituted instead.  Other‐
1580       wise, the tilde-prefix is replaced with the home  directory  associated
1581       with the specified login name.
1582
1583       If  the  tilde-prefix  is  a  `~+', the value of the shell variable PWD
1584       replaces the tilde-prefix.  If the tilde-prefix is a `~-', the value of
1585       the  shell variable OLDPWD, if it is set, is substituted.  If the char‐
1586       acters following the tilde in the tilde-prefix consist of a  number  N,
1587       optionally  prefixed  by  a  `+' or a `-', the tilde-prefix is replaced
1588       with the corresponding element from the directory stack, as it would be
1589       displayed by the dirs builtin invoked with the tilde-prefix as an argu‐
1590       ment.  If the characters following the tilde in the  tilde-prefix  con‐
1591       sist of a number without a leading `+' or `-', `+' is assumed.
1592
1593       If the login name is invalid, or the tilde expansion fails, the word is
1594       unchanged.
1595
1596       Each variable assignment is checked for unquoted tilde-prefixes immedi‐
1597       ately following a : or the first =.  In these cases, tilde expansion is
1598       also performed.  Consequently, one may use  filenames  with  tildes  in
1599       assignments  to  PATH,  MAILPATH, and CDPATH, and the shell assigns the
1600       expanded value.
1601
1602       Bash also performs tilde expansion on words satisfying  the  conditions
1603       of variable assignments (as described above under PARAMETERS) when they
1604       appear as arguments to simple commands.  Bash does not do this,  except
1605       for the declaration commands listed above, when in posix mode.
1606
1607   Parameter Expansion
1608       The `$' character introduces parameter expansion, command substitution,
1609       or arithmetic expansion.  The parameter name or symbol to  be  expanded
1610       may  be enclosed in braces, which are optional but serve to protect the
1611       variable to be expanded from characters immediately following it  which
1612       could be interpreted as part of the name.
1613
1614       When  braces  are  used, the matching ending brace is the first `}' not
1615       escaped by a backslash or within a quoted string,  and  not  within  an
1616       embedded  arithmetic  expansion,  command  substitution,  or  parameter
1617       expansion.
1618
1619       ${parameter}
1620              The value of parameter is substituted.  The braces are  required
1621              when  parameter  is  a  positional  parameter with more than one
1622              digit, or when parameter is followed by a character which is not
1623              to be interpreted as part of its name.  The parameter is a shell
1624              parameter as described above PARAMETERS) or an  array  reference
1625              (Arrays).
1626
1627       If  the  first  character of parameter is an exclamation point (!), and
1628       parameter is not a nameref, it introduces a level of indirection.  Bash
1629       uses  the  value  formed  by expanding the rest of parameter as the new
1630       parameter; this is then expanded and that value is used in the rest  of
1631       the  expansion,  rather  than  the expansion of the original parameter.
1632       This is known as indirect expansion.  The value  is  subject  to  tilde
1633       expansion,  parameter  expansion,  command substitution, and arithmetic
1634       expansion.  If parameter is a nameref, this expands to the name of  the
1635       parameter  referenced  by  parameter instead of performing the complete
1636       indirect expansion.  The exceptions  to  this  are  the  expansions  of
1637       ${!prefix*}  and  ${!name[@]}  described  below.  The exclamation point
1638       must immediately follow the left brace in order to  introduce  indirec‐
1639       tion.
1640
1641       In each of the cases below, word is subject to tilde expansion, parame‐
1642       ter expansion, command substitution, and arithmetic expansion.
1643
1644       When not performing substring expansion,  using  the  forms  documented
1645       below  (e.g.,  :-),  bash  tests for a parameter that is unset or null.
1646       Omitting the colon results in a test  only  for  a  parameter  that  is
1647       unset.
1648
1649       ${parameter:-word}
1650              Use  Default  Values.  If parameter is unset or null, the expan‐
1651              sion of word is substituted.  Otherwise, the value of  parameter
1652              is substituted.
1653       ${parameter:=word}
1654              Assign  Default  Values.   If  parameter  is  unset or null, the
1655              expansion of word is assigned to parameter.  The value of param‐
1656              eter  is  then  substituted.   Positional parameters and special
1657              parameters may not be assigned to in this way.
1658       ${parameter:?word}
1659              Display Error if Null or Unset.  If parameter is null or  unset,
1660              the  expansion  of  word (or a message to that effect if word is
1661              not present) is written to the standard error and the shell,  if
1662              it is not interactive, exits.  Otherwise, the value of parameter
1663              is substituted.
1664       ${parameter:+word}
1665              Use Alternate Value.  If parameter is null or unset, nothing  is
1666              substituted, otherwise the expansion of word is substituted.
1667       ${parameter:offset}
1668       ${parameter:offset:length}
1669              Substring  Expansion.  Expands to up to length characters of the
1670              value of parameter starting at the character specified  by  off‐
1671              set.  If parameter is @, an indexed array subscripted by @ or *,
1672              or an associative array name, the results  differ  as  described
1673              below.   If  length  is omitted, expands to the substring of the
1674              value of parameter starting at the character specified by offset
1675              and  extending  to  the end of the value.  length and offset are
1676              arithmetic expressions (see ARITHMETIC EVALUATION below).
1677
1678              If offset evaluates to a number less than  zero,  the  value  is
1679              used  as  an  offset  in characters from the end of the value of
1680              parameter.  If length evaluates to a number less than  zero,  it
1681              is  interpreted  as  an offset in characters from the end of the
1682              value of parameter rather than a number of characters,  and  the
1683              expansion  is  the  characters  between  offset and that result.
1684              Note that a negative offset must be separated from the colon  by
1685              at  least  one  space to avoid being confused with the :- expan‐
1686              sion.
1687
1688              If parameter is @, the result is  length  positional  parameters
1689              beginning at offset.  A negative offset is taken relative to one
1690              greater than the greatest positional parameter, so an offset  of
1691              -1  evaluates to the last positional parameter.  It is an expan‐
1692              sion error if length evaluates to a number less than zero.
1693
1694              If parameter is an indexed array name subscripted by @ or *, the
1695              result  is  the  length  members  of  the  array  beginning with
1696              ${parameter[offset]}.  A negative offset is  taken  relative  to
1697              one  greater  than the maximum index of the specified array.  It
1698              is an expansion error if length evaluates to a number less  than
1699              zero.
1700
1701              Substring  expansion  applied  to  an associative array produces
1702              undefined results.
1703
1704              Substring indexing is zero-based unless the  positional  parame‐
1705              ters  are  used,  in  which  case  the  indexing  starts at 1 by
1706              default.  If offset is 0,  and  the  positional  parameters  are
1707              used, $0 is prefixed to the list.
1708
1709       ${!prefix*}
1710       ${!prefix@}
1711              Names  matching prefix.  Expands to the names of variables whose
1712              names begin with prefix, separated by the first character of the
1713              IFS  special variable.  When @ is used and the expansion appears
1714              within double quotes, each variable name expands to  a  separate
1715              word.
1716
1717       ${!name[@]}
1718       ${!name[*]}
1719              List  of  array  keys.  If name is an array variable, expands to
1720              the list of array indices (keys) assigned in name.  If  name  is
1721              not  an  array,  expands to 0 if name is set and null otherwise.
1722              When @ is used and the expansion appears within  double  quotes,
1723              each key expands to a separate word.
1724
1725       ${#parameter}
1726              Parameter  length.   The  length  in  characters of the value of
1727              parameter is substituted.  If parameter is *  or  @,  the  value
1728              substituted  is the number of positional parameters.  If parame‐
1729              ter is an array name subscripted by * or @,  the  value  substi‐
1730              tuted  is  the number of elements in the array.  If parameter is
1731              an indexed array name subscripted by  a  negative  number,  that
1732              number  is interpreted as relative to one greater than the maxi‐
1733              mum index of parameter, so negative indices count back from  the
1734              end  of  the  array, and an index of -1 references the last ele‐
1735              ment.
1736
1737       ${parameter#word}
1738       ${parameter##word}
1739              Remove matching prefix pattern.  The word is expanded to produce
1740              a pattern just as in pathname expansion, and matched against the
1741              expanded value of parameter using the rules described under Pat‐
1742              tern  Matching  below.   If the pattern matches the beginning of
1743              the value of parameter, then the result of the expansion is  the
1744              expanded  value  of parameter with the shortest matching pattern
1745              (the ``#'' case) or the longest  matching  pattern  (the  ``##''
1746              case)  deleted.   If  parameter  is  @ or *, the pattern removal
1747              operation is applied to each positional parameter in  turn,  and
1748              the  expansion  is the resultant list.  If parameter is an array
1749              variable subscripted with @ or *, the pattern removal  operation
1750              is  applied  to each member of the array in turn, and the expan‐
1751              sion is the resultant list.
1752
1753       ${parameter%word}
1754       ${parameter%%word}
1755              Remove matching suffix pattern.  The word is expanded to produce
1756              a pattern just as in pathname expansion, and matched against the
1757              expanded value of parameter using the rules described under Pat‐
1758              tern  Matching below.  If the pattern matches a trailing portion
1759              of the expanded value of  parameter,  then  the  result  of  the
1760              expansion  is  the expanded value of parameter with the shortest
1761              matching pattern (the ``%'' case) or the longest  matching  pat‐
1762              tern  (the  ``%%''  case)  deleted.  If parameter is @ or *, the
1763              pattern removal operation is applied to each positional  parame‐
1764              ter in turn, and the expansion is the resultant list.  If param‐
1765              eter is an array variable subscripted with @ or *,  the  pattern
1766              removal  operation  is  applied  to  each member of the array in
1767              turn, and the expansion is the resultant list.
1768
1769       ${parameter/pattern/string}
1770              Pattern substitution.  The pattern is expanded to produce a pat‐
1771              tern  just  as  in pathname expansion, Parameter is expanded and
1772              the longest match of pattern against its value is replaced  with
1773              string.   The match is performed using the rules described under
1774              Pattern Matching below.  If pattern begins with /,  all  matches
1775              of  pattern  are  replaced with string.  Normally only the first
1776              match is replaced.  If pattern begins with #, it must  match  at
1777              the  beginning  of  the expanded value of parameter.  If pattern
1778              begins with %, it must match at the end of the expanded value of
1779              parameter.   If  string  is null, matches of pattern are deleted
1780              and the / following pattern may be omitted.  If the  nocasematch
1781              shell  option  is enabled, the match is performed without regard
1782              to the case of alphabetic characters.  If parameter is @  or  *,
1783              the substitution operation is applied to each positional parame‐
1784              ter in turn, and the expansion is the resultant list.  If param‐
1785              eter is an array variable subscripted with @ or *, the substitu‐
1786              tion operation is applied to each member of the array  in  turn,
1787              and the expansion is the resultant list.
1788
1789       ${parameter^pattern}
1790       ${parameter^^pattern}
1791       ${parameter,pattern}
1792       ${parameter,,pattern}
1793              Case  modification.   This expansion modifies the case of alpha‐
1794              betic characters in parameter.  The pattern is expanded to  pro‐
1795              duce a pattern just as in pathname expansion.  Each character in
1796              the expanded value of parameter is tested against pattern,  and,
1797              if  it  matches the pattern, its case is converted.  The pattern
1798              should not attempt to match more  than  one  character.   The  ^
1799              operator  converts  lowercase letters matching pattern to upper‐
1800              case; the , operator converts matching uppercase letters to low‐
1801              ercase.  The ^^ and ,, expansions convert each matched character
1802              in the expanded value; the ^ and , expansions match and  convert
1803              only  the  first character in the expanded value.  If pattern is
1804              omitted, it is treated like a ?, which matches every  character.
1805              If  parameter  is  @  or  *,  the case modification operation is
1806              applied to each positional parameter in turn, and the  expansion
1807              is  the  resultant list.  If parameter is an array variable sub‐
1808              scripted with @ or *, the case modification operation is applied
1809              to  each  member  of the array in turn, and the expansion is the
1810              resultant list.
1811
1812       ${parameter@operator}
1813              Parameter transformation.  The expansion is either a transforma‐
1814              tion  of  the  value of parameter or information about parameter
1815              itself, depending on the value of operator.  Each operator is  a
1816              single letter:
1817
1818              Q      The  expansion is a string that is the value of parameter
1819                     quoted in a format that can be reused as input.
1820              E      The expansion is a string that is the value of  parameter
1821                     with  backslash  escape  sequences  expanded  as with the
1822                     $'...' quoting mechanism.
1823              P      The expansion is a string that is the result of expanding
1824                     the value of parameter as if it were a prompt string (see
1825                     PROMPTING below).
1826              A      The expansion is a string in the form  of  an  assignment
1827                     statement  or  declare  command  that, if evaluated, will
1828                     recreate parameter with its attributes and value.
1829              a      The expansion is a string consisting of flag values  rep‐
1830                     resenting parameter's attributes.
1831
1832              If  parameter  is @ or *, the operation is applied to each posi‐
1833              tional parameter in turn, and the  expansion  is  the  resultant
1834              list.   If  parameter is an array variable subscripted with @ or
1835              *, the operation is applied to each member of the array in turn,
1836              and the expansion is the resultant list.
1837
1838              The  result  of  the  expansion is subject to word splitting and
1839              pathname expansion as described below.
1840
1841   Command Substitution
1842       Command substitution allows the output of a command to replace the com‐
1843       mand name.  There are two forms:
1844
1845              $(command)
1846       or
1847              `command`
1848
1849       Bash performs the expansion by executing command in a subshell environ‐
1850       ment and replacing the command substitution with the standard output of
1851       the command, with any trailing newlines deleted.  Embedded newlines are
1852       not deleted, but they may be removed during word splitting.   The  com‐
1853       mand  substitution  $(cat  file)  can be replaced by the equivalent but
1854       faster $(< file).
1855
1856       When the old-style backquote form of substitution  is  used,  backslash
1857       retains  its  literal  meaning except when followed by $, `, or \.  The
1858       first backquote not preceded by a backslash terminates the command sub‐
1859       stitution.   When using the $(command) form, all characters between the
1860       parentheses make up the command; none are treated specially.
1861
1862       Command substitutions may be nested.  To nest when using the backquoted
1863       form, escape the inner backquotes with backslashes.
1864
1865       If  the  substitution  appears within double quotes, word splitting and
1866       pathname expansion are not performed on the results.
1867
1868   Arithmetic Expansion
1869       Arithmetic expansion allows the evaluation of an arithmetic  expression
1870       and  the  substitution of the result.  The format for arithmetic expan‐
1871       sion is:
1872
1873              $((expression))
1874
1875       The expression is treated as if it were within  double  quotes,  but  a
1876       double  quote  inside  the  parentheses  is not treated specially.  All
1877       tokens in the expression undergo parameter and variable expansion, com‐
1878       mand  substitution,  and  quote  removal.  The result is treated as the
1879       arithmetic expression to be evaluated.  Arithmetic  expansions  may  be
1880       nested.
1881
1882       The  evaluation  is performed according to the rules listed below under
1883       ARITHMETIC EVALUATION.  If expression is invalid, bash prints a message
1884       indicating failure and no substitution occurs.
1885
1886   Process Substitution
1887       Process  substitution allows a process's input or output to be referred
1888       to using a filename.  It takes the form of  <(list)  or  >(list).   The
1889       process  list is run asynchronously, and its input or output appears as
1890       a filename.  This filename is passed as an argument to the current com‐
1891       mand  as  the  result  of  the expansion.  If the >(list) form is used,
1892       writing to the file will provide input for list.  If the  <(list)  form
1893       is  used,  the  file passed as an argument should be read to obtain the
1894       output of list.  Process substitution is supported on systems that sup‐
1895       port named pipes (FIFOs) or the /dev/fd method of naming open files.
1896
1897       When  available,  process substitution is performed simultaneously with
1898       parameter and variable expansion, command substitution, and  arithmetic
1899       expansion.
1900
1901   Word Splitting
1902       The  shell  scans the results of parameter expansion, command substitu‐
1903       tion, and arithmetic expansion that did not occur within double  quotes
1904       for word splitting.
1905
1906       The  shell  treats each character of IFS as a delimiter, and splits the
1907       results of the other expansions into words using  these  characters  as
1908       field   terminators.   If  IFS  is  unset,  or  its  value  is  exactly
1909       <space><tab><newline>, the default, then sequences of  <space>,  <tab>,
1910       and  <newline>  at the beginning and end of the results of the previous
1911       expansions are ignored, and any sequence of IFS characters not  at  the
1912       beginning  or  end  serves  to delimit words.  If IFS has a value other
1913       than the default, then sequences of the  whitespace  characters  space,
1914       tab,  and  newline are ignored at the beginning and end of the word, as
1915       long as the whitespace character is in the value of IFS (an IFS  white‐
1916       space  character).   Any  character  in IFS that is not IFS whitespace,
1917       along with any adjacent IFS whitespace characters, delimits a field.  A
1918       sequence  of  IFS whitespace characters is also treated as a delimiter.
1919       If the value of IFS is null, no word splitting occurs.
1920
1921       Explicit null arguments ("" or '') are retained and passed to  commands
1922       as empty strings.  Unquoted implicit null arguments, resulting from the
1923       expansion of parameters that have no values, are removed.  If a parame‐
1924       ter  with  no  value  is expanded within double quotes, a null argument
1925       results and is retained and passed to a command  as  an  empty  string.
1926       When  a  quoted null argument appears as part of a word whose expansion
1927       is non-null, the null argument is removed.   That  is,  the  word  -d''
1928       becomes -d after word splitting and null argument removal.
1929
1930       Note that if no expansion occurs, no splitting is performed.
1931
1932   Pathname Expansion
1933       After  word  splitting,  unless  the -f option has been set, bash scans
1934       each word for the characters *, ?, and [.  If one of  these  characters
1935       appears,  then  the word is regarded as a pattern, and replaced with an
1936       alphabetically sorted list of filenames matching the pattern (see  Pat‐
1937       tern  Matching  below).   If  no  matching filenames are found, and the
1938       shell option nullglob is not enabled, the word is left  unchanged.   If
1939       the  nullglob  option  is  set,  and  no matches are found, the word is
1940       removed.  If the failglob shell option  is  set,  and  no  matches  are
1941       found, an error message is printed and the command is not executed.  If
1942       the shell option nocaseglob is enabled, the match is performed  without
1943       regard  to  the  case of alphabetic characters.  When a pattern is used
1944       for pathname expansion, the character ``.''  at the start of a name  or
1945       immediately  following  a  slash must be matched explicitly, unless the
1946       shell option dotglob is set.  The filenames  ``.''   and  ``..''   must
1947       always  be matched explicitly, even if dotglob is set.  In other cases,
1948       the ``.''  character is not treated specially.  When matching  a  path‐
1949       name,  the slash character must always be matched explicitly by a slash
1950       in the pattern, but in other matching contexts it can be matched  by  a
1951       special  pattern  character  as described below under Pattern Matching.
1952       See the description of shopt below under SHELL BUILTIN COMMANDS  for  a
1953       description  of  the  nocaseglob, nullglob, failglob, and dotglob shell
1954       options.
1955
1956       The GLOBIGNORE shell variable may be used to restrict the set  of  file
1957       names  matching  a  pattern.   If GLOBIGNORE is set, each matching file
1958       name that also matches one of the patterns  in  GLOBIGNORE  is  removed
1959       from  the list of matches.  If the nocaseglob option is set, the match‐
1960       ing against the patterns in GLOBIGNORE is performed without  regard  to
1961       case.  The filenames ``.''  and ``..''  are always ignored when GLOBIG‐
1962       NORE is set and not null.  However, setting GLOBIGNORE  to  a  non-null
1963       value has the effect of enabling the dotglob shell option, so all other
1964       filenames beginning with a ``.''  will match.  To get the old  behavior
1965       of  ignoring  filenames beginning with a ``.'', make ``.*''  one of the
1966       patterns in GLOBIGNORE.  The dotglob option is disabled when GLOBIGNORE
1967       is unset.  The pattern matching honors the setting of the extglob shell
1968       option.
1969
1970       Pattern Matching
1971
1972       Any character that appears in a pattern, other than the special pattern
1973       characters  described below, matches itself.  The NUL character may not
1974       occur in a pattern.  A backslash escapes the following  character;  the
1975       escaping  backslash  is  discarded  when matching.  The special pattern
1976       characters must be quoted if they are to be matched literally.
1977
1978       The special pattern characters have the following meanings:
1979
1980              *      Matches any string, including the null string.  When  the
1981                     globstar  shell  option  is  enabled,  and * is used in a
1982                     pathname expansion context, two adjacent  *s  used  as  a
1983                     single  pattern  will  match  all  files and zero or more
1984                     directories and subdirectories.  If followed by a /,  two
1985                     adjacent  *s  will match only directories and subdirecto‐
1986                     ries.
1987              ?      Matches any single character.
1988              [...]  Matches any one of the enclosed characters.   A  pair  of
1989                     characters  separated by a hyphen denotes a range expres‐
1990                     sion; any character that falls between those two  charac‐
1991                     ters,  inclusive,  using  the  current locale's collating
1992                     sequence and character set, is  matched.   If  the  first
1993                     character following the [ is a !  or a ^ then any charac‐
1994                     ter not enclosed is matched.  The sorting order of  char‐
1995                     acters  in range expressions is determined by the current
1996                     locale and the values of the LC_COLLATE or  LC_ALL  shell
1997                     variables, if set.  To obtain the traditional interpreta‐
1998                     tion of range expressions, where [a-d] is  equivalent  to
1999                     [abcd],  set  value of the LC_ALL shell variable to C, or
2000                     enable the globasciiranges shell  option.   A  -  may  be
2001                     matched by including it as the first or last character in
2002                     the set.  A ] may be matched by including it as the first
2003                     character in the set.
2004
2005                     Within  [ and ], character classes can be specified using
2006                     the syntax [:class:], where class is one of the following
2007                     classes defined in the POSIX standard:
2008                     alnum  alpha  ascii  blank  cntrl digit graph lower print
2009                     punct space upper word xdigit
2010                     A character class matches any character belonging to that
2011                     class.  The word character class matches letters, digits,
2012                     and the character _.
2013
2014                     Within [ and ], an equivalence  class  can  be  specified
2015                     using the syntax [=c=], which matches all characters with
2016                     the same collation weight  (as  defined  by  the  current
2017                     locale) as the character c.
2018
2019                     Within [ and ], the syntax [.symbol.] matches the collat‐
2020                     ing symbol symbol.
2021
2022       If the extglob shell option is enabled using the shopt builtin, several
2023       extended  pattern  matching operators are recognized.  In the following
2024       description, a pattern-list is a list of one or more patterns separated
2025       by a |.  Composite patterns may be formed using one or more of the fol‐
2026       lowing sub-patterns:
2027
2028              ?(pattern-list)
2029                     Matches zero or one occurrence of the given patterns
2030              *(pattern-list)
2031                     Matches zero or more occurrences of the given patterns
2032              +(pattern-list)
2033                     Matches one or more occurrences of the given patterns
2034              @(pattern-list)
2035                     Matches one of the given patterns
2036              !(pattern-list)
2037                     Matches anything except one of the given patterns
2038
2039       Complicated extended pattern matching against  long  strings  is  slow,
2040       especially  when the patterns contain alternations and the strings con‐
2041       tain multiple matches.  Using separate matches against shorter strings,
2042       or  using  arrays  of  strings  instead of a single long string, may be
2043       faster.
2044
2045   Quote Removal
2046       After the preceding expansions, all unquoted occurrences of the charac‐
2047       ters  \,  ', and " that did not result from one of the above expansions
2048       are removed.
2049

REDIRECTION

2051       Before a command is executed, its input and output  may  be  redirected
2052       using  a special notation interpreted by the shell.  Redirection allows
2053       commands' file handles to be duplicated, opened, closed, made to  refer
2054       to different files, and can change the files the command reads from and
2055       writes to.  Redirection may also be used to modify file handles in  the
2056       current  shell execution environment.  The following redirection opera‐
2057       tors may precede or appear anywhere within a simple command or may fol‐
2058       low  a  command.   Redirections are processed in the order they appear,
2059       from left to right.
2060
2061       Each redirection that may be preceded by a file descriptor  number  may
2062       instead be preceded by a word of the form {varname}.  In this case, for
2063       each redirection operator except >&- and <&-, the shell will allocate a
2064       file  descriptor  greater than or equal to 10 and assign it to varname.
2065       If >&- or <&- is preceded by {varname}, the value  of  varname  defines
2066       the  file descriptor to close.  If {varname} is supplied, the redirect‐
2067       ion persists beyond the scope of the command, allowing the  shell  pro‐
2068       grammer to manage the file descriptor himself.
2069
2070       In  the  following descriptions, if the file descriptor number is omit‐
2071       ted, and the first character of the redirection operator is <, the  re‐
2072       direction  refers  to  the  standard input (file descriptor 0).  If the
2073       first character of the  redirection  operator  is  >,  the  redirection
2074       refers to the standard output (file descriptor 1).
2075
2076       The  word  following the redirection operator in the following descrip‐
2077       tions, unless otherwise noted, is subjected to brace  expansion,  tilde
2078       expansion,  parameter  and  variable  expansion,  command substitution,
2079       arithmetic expansion,  quote  removal,  pathname  expansion,  and  word
2080       splitting.  If it expands to more than one word, bash reports an error.
2081
2082       Note  that  the order of redirections is significant.  For example, the
2083       command
2084
2085              ls > dirlist 2>&1
2086
2087       directs both standard output and standard error to  the  file  dirlist,
2088       while the command
2089
2090              ls 2>&1 > dirlist
2091
2092       directs  only the standard output to file dirlist, because the standard
2093       error was duplicated from the standard output before the standard  out‐
2094       put was redirected to dirlist.
2095
2096       Bash handles several filenames specially when they are used in redirec‐
2097       tions, as described in the following table.  If the operating system on
2098       which bash is running provides these special files, bash will use them;
2099       otherwise it will emulate them internally with the  behavior  described
2100       below.
2101
2102              /dev/fd/fd
2103                     If  fd  is  a valid integer, file descriptor fd is dupli‐
2104                     cated.
2105              /dev/stdin
2106                     File descriptor 0 is duplicated.
2107              /dev/stdout
2108                     File descriptor 1 is duplicated.
2109              /dev/stderr
2110                     File descriptor 2 is duplicated.
2111              /dev/tcp/host/port
2112                     If host is a valid hostname or Internet address, and port
2113                     is  an integer port number or service name, bash attempts
2114                     to open the corresponding TCP socket.
2115              /dev/udp/host/port
2116                     If host is a valid hostname or Internet address, and port
2117                     is  an integer port number or service name, bash attempts
2118                     to open the corresponding UDP socket.
2119
2120       A failure to open or create a file causes the redirection to fail.
2121
2122       Redirections using file descriptors greater than 9 should be used  with
2123       care,  as they may conflict with file descriptors the shell uses inter‐
2124       nally.
2125
2126   Redirecting Input
2127       Redirection of input causes the file whose name results from the expan‐
2128       sion  of  word  to  be  opened for reading on file descriptor n, or the
2129       standard input (file descriptor 0) if n is not specified.
2130
2131       The general format for redirecting input is:
2132
2133              [n]<word
2134
2135   Redirecting Output
2136       Redirection of output causes the  file  whose  name  results  from  the
2137       expansion of word to be opened for writing on file descriptor n, or the
2138       standard output (file descriptor 1) if n is not specified.  If the file
2139       does  not exist it is created; if it does exist it is truncated to zero
2140       size.
2141
2142       The general format for redirecting output is:
2143
2144              [n]>word
2145
2146       If the redirection operator is >, and the noclobber option to  the  set
2147       builtin  has  been enabled, the redirection will fail if the file whose
2148       name results from the expansion of word exists and is a  regular  file.
2149       If the redirection operator is >|, or the redirection operator is > and
2150       the noclobber option to the set builtin command is not enabled, the re‐
2151       direction is attempted even if the file named by word exists.
2152
2153   Appending Redirected Output
2154       Redirection  of  output  in  this  fashion  causes  the file whose name
2155       results from the expansion of word to be opened for appending  on  file
2156       descriptor  n,  or  the standard output (file descriptor 1) if n is not
2157       specified.  If the file does not exist it is created.
2158
2159       The general format for appending output is:
2160
2161              [n]>>word
2162
2163   Redirecting Standard Output and Standard Error
2164       This construct allows both the standard output (file descriptor 1)  and
2165       the  standard  error output (file descriptor 2) to be redirected to the
2166       file whose name is the expansion of word.
2167
2168       There are two formats for  redirecting  standard  output  and  standard
2169       error:
2170
2171              &>word
2172       and
2173              >&word
2174
2175       Of the two forms, the first is preferred.  This is semantically equiva‐
2176       lent to
2177
2178              >word 2>&1
2179
2180       When using the second form, word may not expand to a number or  -.   If
2181       it  does,  other  redirection  operators  apply  (see  Duplicating File
2182       Descriptors below) for compatibility reasons.
2183
2184   Appending Standard Output and Standard Error
2185       This construct allows both the standard output (file descriptor 1)  and
2186       the  standard  error  output  (file descriptor 2) to be appended to the
2187       file whose name is the expansion of word.
2188
2189       The format for appending standard output and standard error is:
2190
2191              &>>word
2192
2193       This is semantically equivalent to
2194
2195              >>word 2>&1
2196
2197       (see Duplicating File Descriptors below).
2198
2199   Here Documents
2200       This type of redirection instructs the shell to  read  input  from  the
2201       current source until a line containing only delimiter (with no trailing
2202       blanks) is seen.  All of the lines read up to that point are then  used
2203       as  the  standard  input (or file descriptor n if n is specified) for a
2204       command.
2205
2206       The format of here-documents is:
2207
2208              [n]<<[-]word
2209                      here-document
2210              delimiter
2211
2212       No parameter and variable expansion, command  substitution,  arithmetic
2213       expansion,  or pathname expansion is performed on word.  If any part of
2214       word is quoted, the delimiter is the result of quote removal  on  word,
2215       and  the  lines  in  the  here-document  are  not expanded.  If word is
2216       unquoted, all lines of the here-document  are  subjected  to  parameter
2217       expansion,  command substitution, and arithmetic expansion, the charac‐
2218       ter sequence \<newline> is ignored, and \ must be  used  to  quote  the
2219       characters \, $, and `.
2220
2221       If the redirection operator is <<-, then all leading tab characters are
2222       stripped from input lines and  the  line  containing  delimiter.   This
2223       allows  here-documents within shell scripts to be indented in a natural
2224       fashion.
2225
2226   Here Strings
2227       A variant of here documents, the format is:
2228
2229              [n]<<<word
2230
2231       The word undergoes tilde expansion, parameter and  variable  expansion,
2232       command  substitution,  arithmetic expansion, and quote removal.  Path‐
2233       name expansion and word splitting are not  performed.   The  result  is
2234       supplied as a single string, with a newline appended, to the command on
2235       its standard input (or file descriptor n if n is specified).
2236
2237   Duplicating File Descriptors
2238       The redirection operator
2239
2240              [n]<&word
2241
2242       is used to duplicate input file descriptors.  If word expands to one or
2243       more  digits,  the file descriptor denoted by n is made to be a copy of
2244       that file descriptor.  If the digits in word  do  not  specify  a  file
2245       descriptor  open for input, a redirection error occurs.  If word evalu‐
2246       ates to -, file descriptor n is closed.  If n  is  not  specified,  the
2247       standard input (file descriptor 0) is used.
2248
2249       The operator
2250
2251              [n]>&word
2252
2253       is  used  similarly  to duplicate output file descriptors.  If n is not
2254       specified, the standard output (file descriptor 1)  is  used.   If  the
2255       digits  in word do not specify a file descriptor open for output, a re‐
2256       direction error occurs.  If word evaluates to -, file descriptor  n  is
2257       closed.   As  a special case, if n is omitted, and word does not expand
2258       to one or more digits or -, the standard output and standard error  are
2259       redirected as described previously.
2260
2261   Moving File Descriptors
2262       The redirection operator
2263
2264              [n]<&digit-
2265
2266       moves  the  file descriptor digit to file descriptor n, or the standard
2267       input (file descriptor 0) if n is not specified.  digit is closed after
2268       being duplicated to n.
2269
2270       Similarly, the redirection operator
2271
2272              [n]>&digit-
2273
2274       moves  the  file descriptor digit to file descriptor n, or the standard
2275       output (file descriptor 1) if n is not specified.
2276
2277   Opening File Descriptors for Reading and Writing
2278       The redirection operator
2279
2280              [n]<>word
2281
2282       causes the file whose name is the expansion of word to  be  opened  for
2283       both  reading and writing on file descriptor n, or on file descriptor 0
2284       if n is not specified.  If the file does not exist, it is created.
2285

ALIASES

2287       Aliases allow a string to be substituted for a word when it is used  as
2288       the  first  word  of  a  simple command.  The shell maintains a list of
2289       aliases that may be set and unset with the alias  and  unalias  builtin
2290       commands  (see  SHELL  BUILTIN COMMANDS below).  The first word of each
2291       simple command, if unquoted, is checked to see if it has an alias.   If
2292       so,  that word is replaced by the text of the alias.  The characters /,
2293       $, `, and = and any of the shell metacharacters or  quoting  characters
2294       listed above may not appear in an alias name.  The replacement text may
2295       contain any valid shell input,  including  shell  metacharacters.   The
2296       first  word  of  the replacement text is tested for aliases, but a word
2297       that is identical to an alias being expanded is not expanded  a  second
2298       time.   This  means  that  one may alias ls to ls -F, for instance, and
2299       bash does not try to recursively expand the replacement text.   If  the
2300       last  character  of  the  alias value is a blank, then the next command
2301       word following the alias is also checked for alias expansion.
2302
2303       Aliases are created and listed with the alias command, and removed with
2304       the unalias command.
2305
2306       There  is no mechanism for using arguments in the replacement text.  If
2307       arguments are needed, a shell function should be  used  (see  FUNCTIONS
2308       below).
2309
2310       Aliases  are not expanded when the shell is not interactive, unless the
2311       expand_aliases shell option is set using shopt (see the description  of
2312       shopt under SHELL BUILTIN COMMANDS below).
2313
2314       The  rules  concerning  the  definition and use of aliases are somewhat
2315       confusing.  Bash always reads at least one complete line of input,  and
2316       all  lines that make up a compound command, before executing any of the
2317       commands on that line or the compound command.   Aliases  are  expanded
2318       when  a  command is read, not when it is executed.  Therefore, an alias
2319       definition appearing on the same line as another command does not  take
2320       effect  until  the  next line of input is read.  The commands following
2321       the alias definition on that line are not affected by  the  new  alias.
2322       This  behavior  is  also an issue when functions are executed.  Aliases
2323       are expanded when a function definition is read, not when the  function
2324       is  executed,  because a function definition is itself a command.  As a
2325       consequence, aliases defined in a  function  are  not  available  until
2326       after  that function is executed.  To be safe, always put alias defini‐
2327       tions on a separate line, and do not use alias in compound commands.
2328
2329       For almost every purpose, aliases are superseded by shell functions.
2330

FUNCTIONS

2332       A shell function, defined  as  described  above  under  SHELL  GRAMMAR,
2333       stores  a  series  of commands for later execution.  When the name of a
2334       shell function is used as a simple command name, the list  of  commands
2335       associated with that function name is executed.  Functions are executed
2336       in the context of the current shell;  no  new  process  is  created  to
2337       interpret  them  (contrast  this with the execution of a shell script).
2338       When a function is executed, the arguments to the function  become  the
2339       positional parameters during its execution.  The special parameter # is
2340       updated to reflect the change.  Special parameter 0 is unchanged.   The
2341       first  element of the FUNCNAME variable is set to the name of the func‐
2342       tion while the function is executing.
2343
2344       All other aspects of the  shell  execution  environment  are  identical
2345       between  a function and its caller with these exceptions: the DEBUG and
2346       RETURN traps (see the description  of  the  trap  builtin  under  SHELL
2347       BUILTIN  COMMANDS below) are not inherited unless the function has been
2348       given the trace attribute (see the description of the  declare  builtin
2349       below)  or  the -o functrace shell option has been enabled with the set
2350       builtin (in which case all  functions  inherit  the  DEBUG  and  RETURN
2351       traps),  and the ERR trap is not inherited unless the -o errtrace shell
2352       option has been enabled.
2353
2354       Variables local to the function may be declared with the local  builtin
2355       command.  Ordinarily, variables and their values are shared between the
2356       function and its caller.  If a variable is declared  local,  the  vari‐
2357       able's  visible  scope  is restricted to that function and its children
2358       (including the functions it calls).  Local variables "shadow" variables
2359       with  the same name declared at previous scopes.  For instance, a local
2360       variable declared in a function hides a global  variable  of  the  same
2361       name:  references  and assignments refer to the local variable, leaving
2362       the global variable unmodified.  When the function returns, the  global
2363       variable is once again visible.
2364
2365       The  shell  uses  dynamic  scoping  to  control a variable's visibility
2366       within functions.  With dynamic scoping, visible  variables  and  their
2367       values  are a result of the sequence of function calls that caused exe‐
2368       cution to reach the current function.  The value of a variable  that  a
2369       function  sees  depends on its value within its caller, if any, whether
2370       that caller is the "global" scope or another shell function.   This  is
2371       also  the  value  that  a local variable declaration "shadows", and the
2372       value that is restored when the function returns.
2373
2374       For example, if a variable var is declared as local in function  func1,
2375       and  func1  calls  another  function func2, references to var made from
2376       within func2 will resolve to the local variable var from func1, shadow‐
2377       ing any global variable named var.
2378
2379       The unset builtin also acts using the same dynamic scope: if a variable
2380       is local to the current scope, unset will unset it; otherwise the unset
2381       will  refer  to  the  variable  found in any calling scope as described
2382       above.  If a variable at the current local  scope  is  unset,  it  will
2383       remain  so  until  it  is  reset  in  that  scope or until the function
2384       returns.  Once the function returns, any instance of the variable at  a
2385       previous scope will become visible.  If the unset acts on a variable at
2386       a previous scope, any instance of a variable with that  name  that  had
2387       been shadowed will become visible.
2388
2389       The  FUNCNEST  variable,  if  set  to  a  numeric value greater than 0,
2390       defines a maximum function nesting level.   Function  invocations  that
2391       exceed the limit cause the entire command to abort.
2392
2393       If  the  builtin command return is executed in a function, the function
2394       completes and execution resumes with the next command after  the  func‐
2395       tion  call.   Any  command  associated with the RETURN trap is executed
2396       before execution resumes.  When a function completes, the values of the
2397       positional  parameters  and the special parameter # are restored to the
2398       values they had prior to the function's execution.
2399
2400       Function names and definitions may be listed with the -f option to  the
2401       declare or typeset builtin commands.  The -F option to declare or type‐
2402       set will list the function names only (and optionally the  source  file
2403       and  line  number, if the extdebug shell option is enabled).  Functions
2404       may be exported so that subshells automatically have them defined  with
2405       the  -f  option  to  the  export builtin.  A function definition may be
2406       deleted using the -f option to the unset builtin.
2407
2408       Functions may be recursive.  The FUNCNEST variable may be used to limit
2409       the  depth  of the function call stack and restrict the number of func‐
2410       tion invocations.  By default, no limit is imposed  on  the  number  of
2411       recursive calls.
2412

ARITHMETIC EVALUATION

2414       The  shell allows arithmetic expressions to be evaluated, under certain
2415       circumstances (see the let and declare builtin commands,  the  ((  com‐
2416       pound command, and Arithmetic Expansion).  Evaluation is done in fixed-
2417       width integers with no check for overflow,  though  division  by  0  is
2418       trapped  and  flagged as an error.  The operators and their precedence,
2419       associativity, and values are the same as in the C language.  The  fol‐
2420       lowing  list  of  operators  is grouped into levels of equal-precedence
2421       operators.  The levels are listed in order of decreasing precedence.
2422
2423       id++ id--
2424              variable post-increment and post-decrement
2425       - +    unary minus and plus
2426       ++id --id
2427              variable pre-increment and pre-decrement
2428       ! ~    logical and bitwise negation
2429       **     exponentiation
2430       * / %  multiplication, division, remainder
2431       + -    addition, subtraction
2432       << >>  left and right bitwise shifts
2433       <= >= < >
2434              comparison
2435       == !=  equality and inequality
2436       &      bitwise AND
2437       ^      bitwise exclusive OR
2438       |      bitwise OR
2439       &&     logical AND
2440       ||     logical OR
2441       expr?expr:expr
2442              conditional operator
2443       = *= /= %= += -= <<= >>= &= ^= |=
2444              assignment
2445       expr1 , expr2
2446              comma
2447
2448       Shell variables are allowed as operands; parameter  expansion  is  per‐
2449       formed before the expression is evaluated.  Within an expression, shell
2450       variables may also be referenced by name without  using  the  parameter
2451       expansion  syntax.  A shell variable that is null or unset evaluates to
2452       0 when referenced by name without using the parameter expansion syntax.
2453       The  value  of a variable is evaluated as an arithmetic expression when
2454       it is referenced, or when a variable which has been given  the  integer
2455       attribute using declare -i is assigned a value.  A null value evaluates
2456       to 0.  A shell variable need not have its integer attribute  turned  on
2457       to be used in an expression.
2458
2459       Constants with a leading 0 are interpreted as octal numbers.  A leading
2460       0x or  0X  denotes  hexadecimal.   Otherwise,  numbers  take  the  form
2461       [base#]n,  where the optional base is a decimal number between 2 and 64
2462       representing the arithmetic base, and n is a number in that  base.   If
2463       base#  is omitted, then base 10 is used.  When specifying n, the digits
2464       greater than 9 are represented by the lowercase letters, the  uppercase
2465       letters, @, and _, in that order.  If base is less than or equal to 36,
2466       lowercase and uppercase letters may be used interchangeably  to  repre‐
2467       sent numbers between 10 and 35.
2468
2469       Operators  are  evaluated  in  order of precedence.  Sub-expressions in
2470       parentheses are evaluated first and may override the  precedence  rules
2471       above.
2472

CONDITIONAL EXPRESSIONS

2474       Conditional  expressions  are  used  by the [[ compound command and the
2475       test and [ builtin commands to test file attributes and perform  string
2476       and  arithmetic  comparisons.   The test abd [ commands determine their
2477       behavior based on the number of  arguments;  see  the  descriptions  of
2478       those commands for any other command-specific actions.
2479
2480       Expressions  are  formed  from the following unary or binary primaries.
2481       Bash handles several filenames specially when they are used in  expres‐
2482       sions.  If the operating system on which bash is running provides these
2483       special files, bash will use  them;  otherwise  it  will  emulate  them
2484       internally  with this behavior: If any file argument to one of the pri‐
2485       maries is of the form /dev/fd/n, then file descriptor n is checked.  If
2486       the  file  argument  to  one  of  the  primaries  is one of /dev/stdin,
2487       /dev/stdout, or /dev/stderr, file descriptor 0, 1, or 2,  respectively,
2488       is checked.
2489
2490       Unless otherwise specified, primaries that operate on files follow sym‐
2491       bolic links and operate on the target of the link, rather than the link
2492       itself.
2493
2494       When  used  with [[, the < and > operators sort lexicographically using
2495       the current locale.  The test command sorts using ASCII ordering.
2496
2497       -a file
2498              True if file exists.
2499       -b file
2500              True if file exists and is a block special file.
2501       -c file
2502              True if file exists and is a character special file.
2503       -d file
2504              True if file exists and is a directory.
2505       -e file
2506              True if file exists.
2507       -f file
2508              True if file exists and is a regular file.
2509       -g file
2510              True if file exists and is set-group-id.
2511       -h file
2512              True if file exists and is a symbolic link.
2513       -k file
2514              True if file exists and its ``sticky'' bit is set.
2515       -p file
2516              True if file exists and is a named pipe (FIFO).
2517       -r file
2518              True if file exists and is readable.
2519       -s file
2520              True if file exists and has a size greater than zero.
2521       -t fd  True if file descriptor fd is open and refers to a terminal.
2522       -u file
2523              True if file exists and its set-user-id bit is set.
2524       -w file
2525              True if file exists and is writable.
2526       -x file
2527              True if file exists and is executable.
2528       -G file
2529              True if file exists and is owned by the effective group id.
2530       -L file
2531              True if file exists and is a symbolic link.
2532       -N file
2533              True if file exists and has been  modified  since  it  was  last
2534              read.
2535       -O file
2536              True if file exists and is owned by the effective user id.
2537       -S file
2538              True if file exists and is a socket.
2539       file1 -ef file2
2540              True  if file1 and file2 refer to the same device and inode num‐
2541              bers.
2542       file1 -nt file2
2543              True if file1 is newer (according  to  modification  date)  than
2544              file2, or if file1 exists and file2 does not.
2545       file1 -ot file2
2546              True  if file1 is older than file2, or if file2 exists and file1
2547              does not.
2548       -o optname
2549              True if the shell option optname is enabled.  See  the  list  of
2550              options  under  the  description  of  the  -o  option to the set
2551              builtin below.
2552       -v varname
2553              True if the shell variable varname is set (has been  assigned  a
2554              value).
2555       -R varname
2556              True  if  the shell variable varname is set and is a name refer‐
2557              ence.
2558       -z string
2559              True if the length of string is zero.
2560       string
2561       -n string
2562              True if the length of string is non-zero.
2563
2564       string1 == string2
2565       string1 = string2
2566              True if the strings are equal.  = should be used with  the  test
2567              command  for  POSIX conformance.  When used with the [[ command,
2568              this performs pattern matching as described above (Compound Com‐
2569              mands).
2570
2571       string1 != string2
2572              True if the strings are not equal.
2573
2574       string1 < string2
2575              True if string1 sorts before string2 lexicographically.
2576
2577       string1 > string2
2578              True if string1 sorts after string2 lexicographically.
2579
2580       arg1 OP arg2
2581              OP  is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic
2582              binary operators return true if arg1 is equal to, not equal  to,
2583              less  than, less than or equal to, greater than, or greater than
2584              or equal to arg2, respectively.  Arg1 and arg2 may  be  positive
2585              or  negative  integers.  When used with the [[ command, Arg1 and
2586              Arg2 are evaluated as arithmetic  expressions   (see  ARITHMETIC
2587              EVALUATION above).
2588

SIMPLE COMMAND EXPANSION

2590       When  a  simple  command  is executed, the shell performs the following
2591       expansions, assignments, and redirections, from left to right.
2592
2593       1.     The words that the parser has  marked  as  variable  assignments
2594              (those  preceding  the  command name) and redirections are saved
2595              for later processing.
2596
2597       2.     The words that are not variable assignments or redirections  are
2598              expanded.   If  any words remain after expansion, the first word
2599              is taken to be the name of the command and the  remaining  words
2600              are the arguments.
2601
2602       3.     Redirections are performed as described above under REDIRECTION.
2603
2604       4.     The text after the = in each variable assignment undergoes tilde
2605              expansion, parameter expansion, command substitution, arithmetic
2606              expansion,  and quote removal before being assigned to the vari‐
2607              able.
2608
2609       If no command name results, the variable assignments affect the current
2610       shell  environment.  Otherwise, the variables are added to the environ‐
2611       ment of the executed command and do not affect the current shell  envi‐
2612       ronment.   If  any  of  the assignments attempts to assign a value to a
2613       readonly variable, an error occurs, and the command exits with  a  non-
2614       zero status.
2615
2616       If  no  command  name  results,  redirections are performed, but do not
2617       affect the current shell environment.  A redirection error  causes  the
2618       command to exit with a non-zero status.
2619
2620       If  there is a command name left after expansion, execution proceeds as
2621       described below.  Otherwise, the command exits.  If one of  the  expan‐
2622       sions  contained a command substitution, the exit status of the command
2623       is the exit status of the  last  command  substitution  performed.   If
2624       there were no command substitutions, the command exits with a status of
2625       zero.
2626

COMMAND EXECUTION

2628       After a command has been split into words, if it results  in  a  simple
2629       command  and  an  optional list of arguments, the following actions are
2630       taken.
2631
2632       If the command name contains no slashes, the shell attempts  to  locate
2633       it.   If  there  exists a shell function by that name, that function is
2634       invoked as described above in FUNCTIONS.  If the name does not match  a
2635       function,  the shell searches for it in the list of shell builtins.  If
2636       a match is found, that builtin is invoked.
2637
2638       If the name is neither a shell function nor a builtin, and contains  no
2639       slashes,  bash  searches  each element of the PATH for a directory con‐
2640       taining an executable file by that name.  Bash uses  a  hash  table  to
2641       remember  the  full pathnames of executable files (see hash under SHELL
2642       BUILTIN COMMANDS below).  A full search of the directories in  PATH  is
2643       performed  only  if the command is not found in the hash table.  If the
2644       search is unsuccessful, the shell searches for a defined shell function
2645       named command_not_found_handle.  If that function exists, it is invoked
2646       in a separate execution environment with the original command  and  the
2647       original  command's arguments as its arguments, and the function's exit
2648       status becomes the exit status of that subshell.  If that  function  is
2649       not defined, the shell prints an error message and returns an exit sta‐
2650       tus of 127.
2651
2652       If the search is successful, or if the command  name  contains  one  or
2653       more slashes, the shell executes the named program in a separate execu‐
2654       tion environment.  Argument 0 is set to the name given, and the remain‐
2655       ing arguments to the command are set to the arguments given, if any.
2656
2657       If  this  execution fails because the file is not in executable format,
2658       and the file is not a directory, it is assumed to be a shell script,  a
2659       file  containing  shell commands.  A subshell is spawned to execute it.
2660       This subshell reinitializes itself, so that the effect is as if  a  new
2661       shell  had  been  invoked to handle the script, with the exception that
2662       the locations of commands remembered by  the  parent  (see  hash  below
2663       under SHELL BUILTIN COMMANDS) are retained by the child.
2664
2665       If  the program is a file beginning with #!, the remainder of the first
2666       line specifies an interpreter for the program.  The shell executes  the
2667       specified interpreter on operating systems that do not handle this exe‐
2668       cutable format themselves.  The arguments to the interpreter consist of
2669       a  single optional argument following the interpreter name on the first
2670       line of the program, followed by the name of the program,  followed  by
2671       the command arguments, if any.
2672

COMMAND EXECUTION ENVIRONMENT

2674       The  shell  has an execution environment, which consists of the follow‐
2675       ing:
2676
2677       ·      open files inherited by the shell at invocation, as modified  by
2678              redirections supplied to the exec builtin
2679
2680       ·      the  current  working directory as set by cd, pushd, or popd, or
2681              inherited by the shell at invocation
2682
2683       ·      the file creation mode mask as set by umask  or  inherited  from
2684              the shell's parent
2685
2686       ·      current traps set by trap
2687
2688       ·      shell parameters that are set by variable assignment or with set
2689              or inherited from the shell's parent in the environment
2690
2691       ·      shell functions defined during execution or inherited  from  the
2692              shell's parent in the environment
2693
2694       ·      options  enabled  at  invocation (either by default or with com‐
2695              mand-line arguments) or by set
2696
2697       ·      options enabled by shopt
2698
2699       ·      shell aliases defined with alias
2700
2701       ·      various process IDs, including those  of  background  jobs,  the
2702              value of $$, and the value of PPID
2703
2704       When  a  simple command other than a builtin or shell function is to be
2705       executed, it is invoked in a separate execution environment  that  con‐
2706       sists  of the following.  Unless otherwise noted, the values are inher‐
2707       ited from the shell.
2708
2709
2710       ·      the shell's open files, plus  any  modifications  and  additions
2711              specified by redirections to the command
2712
2713       ·      the current working directory
2714
2715       ·      the file creation mode mask
2716
2717       ·      shell  variables  and  functions  marked  for export, along with
2718              variables exported for the command, passed in the environment
2719
2720       ·      traps caught by the shell are reset to the values inherited from
2721              the shell's parent, and traps ignored by the shell are ignored
2722
2723       A  command  invoked  in  this  separate  environment  cannot affect the
2724       shell's execution environment.
2725
2726       Command substitution, commands grouped with parentheses, and  asynchro‐
2727       nous commands are invoked in a subshell environment that is a duplicate
2728       of the shell environment, except that traps caught  by  the  shell  are
2729       reset to the values that the shell inherited from its parent at invoca‐
2730       tion.  Builtin commands that are invoked as part of a pipeline are also
2731       executed in a subshell environment.  Changes made to the subshell envi‐
2732       ronment cannot affect the shell's execution environment.
2733
2734       Subshells spawned to execute command substitutions inherit the value of
2735       the  -e  option  from  the  parent shell.  When not in posix mode, bash
2736       clears the -e option in such subshells.
2737
2738       If a command is followed by a & and job  control  is  not  active,  the
2739       default  standard  input  for  the command is the empty file /dev/null.
2740       Otherwise, the invoked command inherits the  file  descriptors  of  the
2741       calling shell as modified by redirections.
2742

ENVIRONMENT

2744       When  a  program  is invoked it is given an array of strings called the
2745       environment.   This  is  a  list  of  name-value  pairs,  of  the  form
2746       name=value.
2747
2748       The  shell  provides  several  ways  to manipulate the environment.  On
2749       invocation, the shell scans its own environment and creates a parameter
2750       for  each name found, automatically marking it for export to child pro‐
2751       cesses.  Executed commands inherit the  environment.   The  export  and
2752       declare  -x  commands allow parameters and functions to be added to and
2753       deleted from the environment.  If the value of a parameter in the envi‐
2754       ronment  is  modified,  the  new value becomes part of the environment,
2755       replacing the old.  The environment inherited by any  executed  command
2756       consists  of the shell's initial environment, whose values may be modi‐
2757       fied in the shell, less any pairs removed by the  unset  command,  plus
2758       any additions via the export and declare -x commands.
2759
2760       The  environment  for  any  simple command or function may be augmented
2761       temporarily by prefixing it with parameter  assignments,  as  described
2762       above in PARAMETERS.  These assignment statements affect only the envi‐
2763       ronment seen by that command.
2764
2765       If the -k option is set (see the set builtin command below),  then  all
2766       parameter  assignments are placed in the environment for a command, not
2767       just those that precede the command name.
2768
2769       When bash invokes an external command, the variable _  is  set  to  the
2770       full filename of the command and passed to that command in its environ‐
2771       ment.
2772

EXIT STATUS

2774       The exit status of an executed command is the  value  returned  by  the
2775       waitpid system call or equivalent function.  Exit statuses fall between
2776       0 and 255, though, as explained below, the shell may use  values  above
2777       125 specially.  Exit statuses from shell builtins and compound commands
2778       are also limited to this range.  Under certain circumstances, the shell
2779       will use special values to indicate specific failure modes.
2780
2781       For the shell's purposes, a command which exits with a zero exit status
2782       has succeeded.  An exit status of zero indicates success.   A  non-zero
2783       exit  status  indicates  failure.  When a command terminates on a fatal
2784       signal N, bash uses the value of 128+N as the exit status.
2785
2786       If a command is not found, the child  process  created  to  execute  it
2787       returns  a status of 127.  If a command is found but is not executable,
2788       the return status is 126.
2789
2790       If a command fails because of an error during expansion or redirection,
2791       the exit status is greater than zero.
2792
2793       Shell  builtin  commands return a status of 0 (true) if successful, and
2794       non-zero (false) if an error occurs while they execute.   All  builtins
2795       return  an  exit  status  of  2  to indicate incorrect usage, generally
2796       invalid options or missing arguments.
2797
2798       Bash itself returns the exit  status  of  the  last  command  executed,
2799       unless  a  syntax  error occurs, in which case it exits with a non-zero
2800       value.  See also the exit builtin command below.
2801

SIGNALS

2803       When bash is interactive, in the  absence  of  any  traps,  it  ignores
2804       SIGTERM (so that kill 0 does not kill an interactive shell), and SIGINT
2805       is caught and handled (so that the wait builtin is interruptible).   In
2806       all  cases,  bash  ignores  SIGQUIT.  If job control is in effect, bash
2807       ignores SIGTTIN, SIGTTOU, and SIGTSTP.
2808
2809       Non-builtin commands run by bash have signal handlers set to the values
2810       inherited  by  the  shell  from its parent.  When job control is not in
2811       effect, asynchronous commands ignore SIGINT and SIGQUIT in addition  to
2812       these  inherited handlers.  Commands run as a result of command substi‐
2813       tution ignore the keyboard-generated job control signals SIGTTIN, SIGT‐
2814       TOU, and SIGTSTP.
2815
2816       The  shell  exits by default upon receipt of a SIGHUP.  Before exiting,
2817       an interactive shell  resends  the  SIGHUP  to  all  jobs,  running  or
2818       stopped.  Stopped jobs are sent SIGCONT to ensure that they receive the
2819       SIGHUP.  To prevent the shell from sending the signal to  a  particular
2820       job,  it  should be removed from the jobs table with the disown builtin
2821       (see SHELL BUILTIN COMMANDS below) or  marked  to  not  receive  SIGHUP
2822       using disown -h.
2823
2824       If  the  huponexit  shell  option has been set with shopt, bash sends a
2825       SIGHUP to all jobs when an interactive login shell exits.
2826
2827       If bash is waiting for a command to complete and receives a signal  for
2828       which a trap has been set, the trap will not be executed until the com‐
2829       mand completes.  When bash is waiting for an asynchronous  command  via
2830       the  wait  builtin, the reception of a signal for which a trap has been
2831       set will cause the wait builtin to return immediately with an exit sta‐
2832       tus greater than 128, immediately after which the trap is executed.
2833

JOB CONTROL

2835       Job  control  refers  to  the ability to selectively stop (suspend) the
2836       execution of processes and continue (resume) their execution at a later
2837       point.   A  user  typically  employs  this  facility via an interactive
2838       interface supplied jointly by the operating  system  kernel's  terminal
2839       driver and bash.
2840
2841       The  shell  associates  a  job with each pipeline.  It keeps a table of
2842       currently executing jobs, which may be listed with  the  jobs  command.
2843       When  bash starts a job asynchronously (in the background), it prints a
2844       line that looks like:
2845
2846              [1] 25647
2847
2848       indicating that this job is job number 1 and that the process ID of the
2849       last process in the pipeline associated with this job is 25647.  All of
2850       the processes in a single pipeline are members of the same  job.   Bash
2851       uses the job abstraction as the basis for job control.
2852
2853       To  facilitate the implementation of the user interface to job control,
2854       the operating system maintains the notion of a current terminal process
2855       group ID.  Members of this process group (processes whose process group
2856       ID is equal to the current terminal process group ID) receive keyboard-
2857       generated  signals  such  as SIGINT.  These processes are said to be in
2858       the foreground.  Background processes are those whose process group  ID
2859       differs from the terminal's; such processes are immune to keyboard-gen‐
2860       erated signals.  Only foreground processes are allowed to read from or,
2861       if  the  user  so  specifies  with  stty tostop, write to the terminal.
2862       Background processes which attempt to read from  (write  to  when  stty
2863       tostop  is  in effect) the terminal are sent a SIGTTIN (SIGTTOU) signal
2864       by the kernel's terminal driver, which,  unless  caught,  suspends  the
2865       process.
2866
2867       If  the operating system on which bash is running supports job control,
2868       bash contains facilities to use it.  Typing the suspend character (typ‐
2869       ically ^Z, Control-Z) while a process is running causes that process to
2870       be stopped and returns control to bash.   Typing  the  delayed  suspend
2871       character  (typically  ^Y,  Control-Y) causes the process to be stopped
2872       when it attempts to read input from the terminal,  and  control  to  be
2873       returned  to bash.  The user may then manipulate the state of this job,
2874       using the bg command to continue it in the background, the  fg  command
2875       to continue it in the foreground, or the kill command to kill it.  A ^Z
2876       takes effect immediately, and has the additional side effect of causing
2877       pending output and typeahead to be discarded.
2878
2879       There are a number of ways to refer to a job in the shell.  The charac‐
2880       ter % introduces a job specification (jobspec).  Job number  n  may  be
2881       referred to as %n.  A job may also be referred to using a prefix of the
2882       name used to start it, or using a substring that appears in its command
2883       line.   For  example,  %ce  refers  to  a  stopped ce job.  If a prefix
2884       matches more than one job, bash reports an error.  Using %?ce,  on  the
2885       other  hand,  refers to any job containing the string ce in its command
2886       line.  If the substring matches more than  one  job,  bash  reports  an
2887       error.   The  symbols %% and %+ refer to the shell's notion of the cur‐
2888       rent job, which is the last job stopped while it was in the  foreground
2889       or started in the background.  The previous job may be referenced using
2890       %-.  If there is only a single job, %+ and %- can both be used to refer
2891       to  that  job.   In  output pertaining to jobs (e.g., the output of the
2892       jobs command), the current job is always flagged with a +, and the pre‐
2893       vious  job  with  a -.  A single % (with no accompanying job specifica‐
2894       tion) also refers to the current job.
2895
2896       Simply naming a job can be used to bring it into the foreground: %1  is
2897       a  synonym  for  ``fg %1'', bringing job 1 from the background into the
2898       foreground.  Similarly, ``%1 &''  resumes  job  1  in  the  background,
2899       equivalent to ``bg %1''.
2900
2901       The  shell  learns immediately whenever a job changes state.  Normally,
2902       bash waits until it is about to print a prompt before reporting changes
2903       in  a  job's status so as to not interrupt any other output.  If the -b
2904       option to the set builtin command is enabled, bash reports such changes
2905       immediately.   Any  trap  on  SIGCHLD  is  executed for each child that
2906       exits.
2907
2908       If an attempt to exit bash is made while jobs are stopped (or,  if  the
2909       checkjobs  shell  option has been enabled using the shopt builtin, run‐
2910       ning), the shell prints a warning message, and, if the checkjobs option
2911       is  enabled,  lists  the jobs and their statuses.  The jobs command may
2912       then be used to inspect their status.  If a second attempt to  exit  is
2913       made  without  an intervening command, the shell does not print another
2914       warning, and any stopped jobs are terminated.
2915
2916       When the shell is waiting for a job or process using the wait  builtin,
2917       and  job  control  is  enabled,  wait  will return when the job changes
2918       state. The -f option will force wait to wait until the job  or  process
2919       terminates before returning.
2920

PROMPTING

2922       When executing interactively, bash displays the primary prompt PS1 when
2923       it is ready to read a command, and the secondary  prompt  PS2  when  it
2924       needs  more  input  to  complete a command.  Bash displays PS0 after it
2925       reads a  command  but  before  executing  it.   Bash  displays  PS4  as
2926       described  above  before  tracing  each  command  when the -x option is
2927       enabled.  Bash allows these prompt strings to be customized by  insert‐
2928       ing  a  number of backslash-escaped special characters that are decoded
2929       as follows:
2930              \a     an ASCII bell character (07)
2931              \d     the date in "Weekday Month Date" format (e.g.,  "Tue  May
2932                     26")
2933              \D{format}
2934                     the  format  is  passed  to strftime(3) and the result is
2935                     inserted into the prompt string; an empty format  results
2936                     in a locale-specific time representation.  The braces are
2937                     required
2938              \e     an ASCII escape character (033)
2939              \h     the hostname up to the first `.'
2940              \H     the hostname
2941              \j     the number of jobs currently managed by the shell
2942              \l     the basename of the shell's terminal device name
2943              \n     newline
2944              \r     carriage return
2945              \s     the name of the shell, the basename of  $0  (the  portion
2946                     following the final slash)
2947              \t     the current time in 24-hour HH:MM:SS format
2948              \T     the current time in 12-hour HH:MM:SS format
2949              \@     the current time in 12-hour am/pm format
2950              \A     the current time in 24-hour HH:MM format
2951              \u     the username of the current user
2952              \v     the version of bash (e.g., 2.00)
2953              \V     the release of bash, version + patch level (e.g., 2.00.0)
2954              \w     the  current  working  directory,  with $HOME abbreviated
2955                     with a tilde (uses the value of the PROMPT_DIRTRIM  vari‐
2956                     able)
2957              \W     the basename of the current working directory, with $HOME
2958                     abbreviated with a tilde
2959              \!     the history number of this command
2960              \#     the command number of this command
2961              \$     if the effective UID is 0, a #, otherwise a $
2962              \nnn   the character corresponding to the octal number nnn
2963              \\     a backslash
2964              \[     begin a sequence of non-printing characters, which  could
2965                     be  used  to  embed  a terminal control sequence into the
2966                     prompt
2967              \]     end a sequence of non-printing characters
2968
2969       The command number and the history number are  usually  different:  the
2970       history  number of a command is its position in the history list, which
2971       may include commands  restored  from  the  history  file  (see  HISTORY
2972       below),  while  the  command  number is the position in the sequence of
2973       commands executed during the current shell session.  After  the  string
2974       is  decoded,  it is expanded via parameter expansion, command substitu‐
2975       tion, arithmetic expansion, and quote removal, subject to the value  of
2976       the  promptvars  shell option (see the description of the shopt command
2977       under SHELL BUILTIN COMMANDS below).
2978

READLINE

2980       This is the library that handles reading input when using  an  interac‐
2981       tive shell, unless the --noediting option is given at shell invocation.
2982       Line editing is also used when using the -e option to the read builtin.
2983       By default, the line editing commands are similar to those of Emacs.  A
2984       vi-style line editing interface is also available.  Line editing can be
2985       enabled  at  any  time  using  the -o emacs or -o vi options to the set
2986       builtin (see SHELL BUILTIN COMMANDS below).  To turn off  line  editing
2987       after  the  shell  is running, use the +o emacs or +o vi options to the
2988       set builtin.
2989
2990   Readline Notation
2991       In this section, the Emacs-style notation is used to denote keystrokes.
2992       Control  keys  are  denoted by C-key, e.g., C-n means Control-N.  Simi‐
2993       larly, meta keys are denoted by M-key, so M-x means Meta-X.   (On  key‐
2994       boards  without a meta key, M-x means ESC x, i.e., press the Escape key
2995       then the x key.  This makes ESC the meta prefix.  The combination M-C-x
2996       means  ESC-Control-x, or press the Escape key then hold the Control key
2997       while pressing the x key.)
2998
2999       Readline commands may be given numeric arguments, which normally act as
3000       a  repeat  count.   Sometimes,  however, it is the sign of the argument
3001       that is significant.  Passing a negative argument  to  a  command  that
3002       acts  in the forward direction (e.g., kill-line) causes that command to
3003       act in a backward direction.  Commands whose  behavior  with  arguments
3004       deviates from this are noted below.
3005
3006       When  a command is described as killing text, the text deleted is saved
3007       for possible future retrieval (yanking).  The killed text is saved in a
3008       kill ring.  Consecutive kills cause the text to be accumulated into one
3009       unit, which can be yanked all at once.  Commands which do not kill text
3010       separate the chunks of text on the kill ring.
3011
3012   Readline Initialization
3013       Readline  is  customized  by putting commands in an initialization file
3014       (the inputrc file).  The name of this file is taken from the  value  of
3015       the  INPUTRC  variable.   If  that  variable  is  unset, the default is
3016       ~/.inputrc.  When a program which uses the readline library starts  up,
3017       the initialization file is read, and the key bindings and variables are
3018       set.  There are only a few basic constructs  allowed  in  the  readline
3019       initialization  file.  Blank lines are ignored.  Lines beginning with a
3020       # are comments.  Lines beginning with a  $  indicate  conditional  con‐
3021       structs.  Other lines denote key bindings and variable settings.
3022
3023       The  default  key-bindings  may be changed with an inputrc file.  Other
3024       programs that use this library may add their own commands and bindings.
3025
3026       For example, placing
3027
3028              M-Control-u: universal-argument
3029       or
3030              C-Meta-u: universal-argument
3031       into the inputrc would make M-C-u execute the readline command  univer‐
3032       sal-argument.
3033
3034       The  following  symbolic  character  names are recognized: RUBOUT, DEL,
3035       ESC, LFD, NEWLINE, RET, RETURN, SPC, SPACE, and TAB.
3036
3037       In addition to command names, readline allows keys to  be  bound  to  a
3038       string that is inserted when the key is pressed (a macro).
3039
3040   Readline Key Bindings
3041       The  syntax for controlling key bindings in the inputrc file is simple.
3042       All that is required is the name of the command or the text of a  macro
3043       and a key sequence to which it should be bound.  The name may be speci‐
3044       fied in one of two ways: as a symbolic key name, possibly with Meta- or
3045       Control- prefixes, or as a key sequence.
3046
3047       When using the form keyname:function-name or macro, keyname is the name
3048       of a key spelled out in English.  For example:
3049
3050              Control-u: universal-argument
3051              Meta-Rubout: backward-kill-word
3052              Control-o: "> output"
3053
3054       In the above example, C-u is bound to the function  universal-argument,
3055       M-DEL  is bound to the function backward-kill-word, and C-o is bound to
3056       run the macro expressed on the right hand side (that is, to insert  the
3057       text ``> output'' into the line).
3058
3059       In  the  second  form,  "keyseq":function-name or macro, keyseq differs
3060       from keyname above in that strings denoting an entire key sequence  may
3061       be  specified  by  placing the sequence within double quotes.  Some GNU
3062       Emacs style key escapes can be used, as in the following  example,  but
3063       the symbolic character names are not recognized.
3064
3065              "\C-u": universal-argument
3066              "\C-x\C-r": re-read-init-file
3067              "\e[11~": "Function Key 1"
3068
3069       In this example, C-u is again bound to the function universal-argument.
3070       C-x C-r is bound to the function re-read-init-file, and ESC [ 1 1 ~  is
3071       bound to insert the text ``Function Key 1''.
3072
3073       The full set of GNU Emacs style escape sequences is
3074              \C-    control prefix
3075              \M-    meta prefix
3076              \e     an escape character
3077              \\     backslash
3078              \"     literal "
3079              \'     literal '
3080
3081       In  addition  to  the GNU Emacs style escape sequences, a second set of
3082       backslash escapes is available:
3083              \a     alert (bell)
3084              \b     backspace
3085              \d     delete
3086              \f     form feed
3087              \n     newline
3088              \r     carriage return
3089              \t     horizontal tab
3090              \v     vertical tab
3091              \nnn   the eight-bit character whose value is  the  octal  value
3092                     nnn (one to three digits)
3093              \xHH   the  eight-bit  character  whose value is the hexadecimal
3094                     value HH (one or two hex digits)
3095
3096       When entering the text of a macro, single or double quotes must be used
3097       to indicate a macro definition.  Unquoted text is assumed to be a func‐
3098       tion name.  In the macro body, the backslash  escapes  described  above
3099       are  expanded.   Backslash  will quote any other character in the macro
3100       text, including " and '.
3101
3102       Bash allows the current readline key bindings to be displayed or  modi‐
3103       fied  with  the bind builtin command.  The editing mode may be switched
3104       during interactive use by using the -o option to the set  builtin  com‐
3105       mand (see SHELL BUILTIN COMMANDS below).
3106
3107   Readline Variables
3108       Readline has variables that can be used to further customize its behav‐
3109       ior.  A variable may be set in the inputrc file with a statement of the
3110       form
3111
3112              set variable-name value
3113
3114       Except  where  noted,  readline variables can take the values On or Off
3115       (without regard to case).  Unrecognized  variable  names  are  ignored.
3116       When  a variable value is read, empty or null values, "on" (case-insen‐
3117       sitive), and "1" are equivalent to On.  All other values are equivalent
3118       to Off.  The variables and their default values are:
3119
3120       bell-style (audible)
3121              Controls  what  happens when readline wants to ring the terminal
3122              bell.  If set to none, readline never rings the bell.  If set to
3123              visible,  readline  uses a visible bell if one is available.  If
3124              set to audible, readline attempts to ring the terminal's bell.
3125       bind-tty-special-chars (On)
3126              If set to On, readline attempts to bind the  control  characters
3127              treated specially by the kernel's terminal driver to their read‐
3128              line equivalents.
3129       blink-matching-paren (Off)
3130              If set to On, readline attempts to briefly move the cursor to an
3131              opening parenthesis when a closing parenthesis is inserted.
3132       colored-completion-prefix (Off)
3133              If  set  to  On, when listing completions, readline displays the
3134              common prefix of the set of possible completions using a differ‐
3135              ent  color.   The  color definitions are taken from the value of
3136              the LS_COLORS environment variable.
3137       colored-stats (Off)
3138              If set to On, readline displays possible completions using  dif‐
3139              ferent  colors  to  indicate their file type.  The color defini‐
3140              tions are taken from the  value  of  the  LS_COLORS  environment
3141              variable.
3142       comment-begin (``#'')
3143              The  string  that  is  inserted when the readline insert-comment
3144              command is executed.  This command is bound to M-# in emacs mode
3145              and to # in vi command mode.
3146       completion-display-width (-1)
3147              The  number  of  screen columns used to display possible matches
3148              when performing completion.  The value is ignored if it is  less
3149              than  0 or greater than the terminal screen width.  A value of 0
3150              will cause matches to be displayed one per  line.   The  default
3151              value is -1.
3152       completion-ignore-case (Off)
3153              If set to On, readline performs filename matching and completion
3154              in a case-insensitive fashion.
3155       completion-map-case (Off)
3156              If set to On, and completion-ignore-case  is  enabled,  readline
3157              treats  hyphens  (-) and underscores (_) as equivalent when per‐
3158              forming case-insensitive filename matching and completion.
3159       completion-prefix-display-length (0)
3160              The length in characters of the common prefix of a list of  pos‐
3161              sible  completions that is displayed without modification.  When
3162              set to a value greater than zero, common  prefixes  longer  than
3163              this  value are replaced with an ellipsis when displaying possi‐
3164              ble completions.
3165       completion-query-items (100)
3166              This determines when the user is queried about viewing the  num‐
3167              ber  of  possible  completions generated by the possible-comple‐
3168              tions command.  It may be set to any integer value greater  than
3169              or  equal  to  zero.   If  the number of possible completions is
3170              greater than or equal to the value of this variable, the user is
3171              asked  whether or not he wishes to view them; otherwise they are
3172              simply listed on the terminal.
3173       convert-meta (On)
3174              If set to On, readline will convert characters with  the  eighth
3175              bit set to an ASCII key sequence by stripping the eighth bit and
3176              prefixing an escape character (in effect, using  escape  as  the
3177              meta  prefix).   The  default is On, but readline will set it to
3178              Off if the locale contains eight-bit characters.
3179       disable-completion (Off)
3180              If set to On, readline will inhibit word completion.  Completion
3181              characters  will  be  inserted into the line as if they had been
3182              mapped to self-insert.
3183       echo-control-characters (On)
3184              When set to On, on operating systems that indicate they  support
3185              it, readline echoes a character corresponding to a signal gener‐
3186              ated from the keyboard.
3187       editing-mode (emacs)
3188              Controls whether readline begins with a set of key bindings sim‐
3189              ilar to Emacs or vi.  editing-mode can be set to either emacs or
3190              vi.
3191       emacs-mode-string (@)
3192              If the show-mode-in-prompt variable is enabled, this  string  is
3193              displayed immediately before the last line of the primary prompt
3194              when emacs editing mode is active.  The value is expanded like a
3195              key  binding,  so the standard set of meta- and control prefixes
3196              and backslash escape sequences is available.  Use the \1 and  \2
3197              escapes  to  begin and end sequences of non-printing characters,
3198              which can be used to embed a terminal control sequence into  the
3199              mode string.
3200       enable-bracketed-paste (Off)
3201              When  set  to  On, readline will configure the terminal in a way
3202              that will enable it to insert each paste into the editing buffer
3203              as a single string of characters, instead of treating each char‐
3204              acter as if it had been read from the keyboard.  This  can  pre‐
3205              vent  pasted  characters  from being interpreted as editing com‐
3206              mands.
3207       enable-keypad (Off)
3208              When set to On, readline will try to enable the application key‐
3209              pad  when  it  is  called.  Some systems need this to enable the
3210              arrow keys.
3211       enable-meta-key (On)
3212              When set to On, readline will try to enable  any  meta  modifier
3213              key  the  terminal claims to support when it is called.  On many
3214              terminals, the meta key is used to send eight-bit characters.
3215       expand-tilde (Off)
3216              If set  to  On,  tilde  expansion  is  performed  when  readline
3217              attempts word completion.
3218       history-preserve-point (Off)
3219              If  set  to  On, the history code attempts to place point at the
3220              same location on each history line retrieved with  previous-his‐
3221              tory or next-history.
3222       history-size (unset)
3223              Set  the  maximum number of history entries saved in the history
3224              list.  If set to zero, any existing history entries are  deleted
3225              and no new entries are saved.  If set to a value less than zero,
3226              the number of history entries is not limited.  By  default,  the
3227              number  of  history  entries is set to the value of the HISTSIZE
3228              shell variable.  If an attempt is made to set history-size to  a
3229              non-numeric value, the maximum number of history entries will be
3230              set to 500.
3231       horizontal-scroll-mode (Off)
3232              When set to On, makes readline use a single  line  for  display,
3233              scrolling the input horizontally on a single screen line when it
3234              becomes longer than the screen width rather than wrapping  to  a
3235              new line.
3236       input-meta (Off)
3237              If  set to On, readline will enable eight-bit input (that is, it
3238              will not strip the eighth bit from  the  characters  it  reads),
3239              regardless of what the terminal claims it can support.  The name
3240              meta-flag is a synonym for this variable.  The default  is  Off,
3241              but  readline will set it to On if the locale contains eight-bit
3242              characters.
3243       isearch-terminators (``C-[C-J'')
3244              The string of characters that should  terminate  an  incremental
3245              search  without  subsequently  executing the character as a com‐
3246              mand.  If this variable has not been given a value, the  charac‐
3247              ters ESC and C-J will terminate an incremental search.
3248       keymap (emacs)
3249              Set  the current readline keymap.  The set of valid keymap names
3250              is emacs, emacs-standard, emacs-meta,  emacs-ctlx,  vi,  vi-com‐
3251              mand,  and  vi-insert.  vi is equivalent to vi-command; emacs is
3252              equivalent to emacs-standard.  The default value is  emacs;  the
3253              value of editing-mode also affects the default keymap.
3254       keyseq-timeout (500)
3255              Specifies  the  duration readline will wait for a character when
3256              reading an ambiguous key sequence (one that can form a  complete
3257              key sequence using the input read so far, or can take additional
3258              input to complete a  longer  key  sequence).   If  no  input  is
3259              received  within  the timeout, readline will use the shorter but
3260              complete key sequence.  The value is specified in  milliseconds,
3261              so  a value of 1000 means that readline will wait one second for
3262              additional input.  If this variable is set to a value less  than
3263              or  equal to zero, or to a non-numeric value, readline will wait
3264              until another key is pressed to decide  which  key  sequence  to
3265              complete.
3266       mark-directories (On)
3267              If set to On, completed directory names have a slash appended.
3268       mark-modified-lines (Off)
3269              If  set  to  On,  history lines that have been modified are dis‐
3270              played with a preceding asterisk (*).
3271       mark-symlinked-directories (Off)
3272              If set to On, completed names which are symbolic links to direc‐
3273              tories   have   a  slash  appended  (subject  to  the  value  of
3274              mark-directories).
3275       match-hidden-files (On)
3276              This variable, when set to On, causes readline  to  match  files
3277              whose  names  begin  with  a  `.' (hidden files) when performing
3278              filename completion.  If set to Off, the  leading  `.'  must  be
3279              supplied by the user in the filename to be completed.
3280       menu-complete-display-prefix (Off)
3281              If  set to On, menu completion displays the common prefix of the
3282              list of possible completions (which may be empty) before cycling
3283              through the list.
3284       output-meta (Off)
3285              If  set  to On, readline will display characters with the eighth
3286              bit set directly rather than as a meta-prefixed escape sequence.
3287              The default is Off, but readline will set it to On if the locale
3288              contains eight-bit characters.
3289       page-completions (On)
3290              If set to On, readline uses an internal more-like pager to  dis‐
3291              play a screenful of possible completions at a time.
3292       print-completions-horizontally (Off)
3293              If  set  to  On,  readline will display completions with matches
3294              sorted horizontally in alphabetical order, rather than down  the
3295              screen.
3296       revert-all-at-newline (Off)
3297              If  set  to  On, readline will undo all changes to history lines
3298              before returning when accept-line is executed.  By default, his‐
3299              tory  lines  may  be  modified  and retain individual undo lists
3300              across calls to readline.
3301       show-all-if-ambiguous (Off)
3302              This alters the default behavior of  the  completion  functions.
3303              If set to On, words which have more than one possible completion
3304              cause the matches to be listed immediately  instead  of  ringing
3305              the bell.
3306       show-all-if-unmodified (Off)
3307              This  alters the default behavior of the completion functions in
3308              a fashion similar to show-all-if-ambiguous.  If set to On, words
3309              which  have more than one possible completion without any possi‐
3310              ble partial completion (the possible completions don't  share  a
3311              common  prefix)  cause  the  matches  to  be  listed immediately
3312              instead of ringing the bell.
3313       show-mode-in-prompt (Off)
3314              If set to On, add a string to the beginning of the prompt  indi‐
3315              cating  the  editing  mode:  emacs, vi command, or vi insertion.
3316              The mode strings are user-settable (e.g., emacs-mode-string).
3317       skip-completed-text (Off)
3318              If set to On, this alters the default completion  behavior  when
3319              inserting  a  single match into the line.  It's only active when
3320              performing completion in the middle  of  a  word.   If  enabled,
3321              readline  does  not  insert  characters from the completion that
3322              match characters after point in the  word  being  completed,  so
3323              portions of the word following the cursor are not duplicated.
3324       vi-cmd-mode-string ((cmd))
3325              If  the  show-mode-in-prompt variable is enabled, this string is
3326              displayed immediately before the last line of the primary prompt
3327              when  vi  editing mode is active and in command mode.  The value
3328              is expanded like a key binding, so the standard set of meta- and
3329              control  prefixes  and  backslash escape sequences is available.
3330              Use the \1 and \2 escapes to begin and  end  sequences  of  non-
3331              printing  characters, which can be used to embed a terminal con‐
3332              trol sequence into the mode string.
3333       vi-ins-mode-string ((ins))
3334              If the show-mode-in-prompt variable is enabled, this  string  is
3335              displayed immediately before the last line of the primary prompt
3336              when vi editing mode is active and in insertion mode.  The value
3337              is expanded like a key binding, so the standard set of meta- and
3338              control prefixes and backslash escape  sequences  is  available.
3339              Use  the  \1  and  \2 escapes to begin and end sequences of non-
3340              printing characters, which can be used to embed a terminal  con‐
3341              trol sequence into the mode string.
3342       visible-stats (Off)
3343              If  set to On, a character denoting a file's type as reported by
3344              stat(2) is appended to the filename when listing  possible  com‐
3345              pletions.
3346
3347   Readline Conditional Constructs
3348       Readline  implements  a  facility  similar in spirit to the conditional
3349       compilation features of the C preprocessor which  allows  key  bindings
3350       and  variable  settings  to be performed as the result of tests.  There
3351       are four parser directives used.
3352
3353       $if    The $if construct allows bindings to be made based on the  edit‐
3354              ing  mode,  the  terminal  being  used, or the application using
3355              readline.  The text of the test, after any comparison operator,
3356               extends to the end of the  line;  unless  otherwise  noted,  no
3357              characters are required to isolate it.
3358
3359              mode   The  mode=  form  of  the  $if  directive is used to test
3360                     whether readline is in emacs or vi  mode.   This  may  be
3361                     used  in  conjunction  with  the  set keymap command, for
3362                     instance, to  set  bindings  in  the  emacs-standard  and
3363                     emacs-ctlx  keymaps  only  if readline is starting out in
3364                     emacs mode.
3365
3366              term   The term= form may be used to  include  terminal-specific
3367                     key bindings, perhaps to bind the key sequences output by
3368                     the terminal's function keys.  The word on the right side
3369                     of the = is tested against both the full name of the ter‐
3370                     minal and the portion of the  terminal  name  before  the
3371                     first  -.  This allows sun to match both sun and sun-cmd,
3372                     for instance.
3373
3374              version
3375                     The version test  may  be  used  to  perform  comparisons
3376                     against  specific readline versions.  The version expands
3377                     to the current readline version.  The set  of  comparison
3378                     operators  includes  =,  (and  ==), !=, <=, >=, <, and >.
3379                     The version number supplied on  the  right  side  of  the
3380                     operator  consists of a major version number, an optional
3381                     decimal point, and an optional minor version (e.g., 7.1).
3382                     If  the  minor version is omitted, it is assumed to be 0.
3383                     The operator may be separated from the string version and
3384                     from the version number argument by whitespace.
3385
3386              application
3387                     The application construct is used to include application-
3388                     specific  settings.   Each  program  using  the  readline
3389                     library  sets the application name, and an initialization
3390                     file can test for a particular value.  This could be used
3391                     to  bind key sequences to functions useful for a specific
3392                     program.  For instance, the following command adds a  key
3393                     sequence  that  quotes  the  current  or previous word in
3394                     bash:
3395
3396                     $if Bash
3397                     # Quote the current or previous word
3398                     "\C-xq": "\eb\"\ef\""
3399                     $endif
3400
3401              variable
3402                     The variable construct provides simple equality tests for
3403                     readline  variables and values.  The permitted comparison
3404                     operators are =, ==, and !=.  The variable name  must  be
3405                     separated from the comparison operator by whitespace; the
3406                     operator may be separated from the  value  on  the  right
3407                     hand  side  by whitespace.  Both string and boolean vari‐
3408                     ables may be tested. Boolean  variables  must  be  tested
3409                     against the values on and off.
3410
3411       $endif This command, as seen in the previous example, terminates an $if
3412              command.
3413
3414       $else  Commands in this branch of the $if directive are executed if the
3415              test fails.
3416
3417       $include
3418              This  directive takes a single filename as an argument and reads
3419              commands and bindings from that file.  For example, the  follow‐
3420              ing directive would read /etc/inputrc:
3421
3422              $include  /etc/inputrc
3423
3424   Searching
3425       Readline  provides  commands  for searching through the command history
3426       (see HISTORY below) for lines containing a specified string.  There are
3427       two search modes: incremental and non-incremental.
3428
3429       Incremental  searches  begin  before  the  user has finished typing the
3430       search string.  As each character of the search string is typed,  read‐
3431       line displays the next entry from the history matching the string typed
3432       so far.  An incremental search requires  only  as  many  characters  as
3433       needed  to  find  the desired history entry.  The characters present in
3434       the value of the isearch-terminators variable are used to terminate  an
3435       incremental search.  If that variable has not been assigned a value the
3436       Escape and Control-J characters will terminate an  incremental  search.
3437       Control-G  will  abort  an  incremental search and restore the original
3438       line.  When the search is terminated, the history entry containing  the
3439       search string becomes the current line.
3440
3441       To  find  other matching entries in the history list, type Control-S or
3442       Control-R as appropriate.  This will search backward or forward in  the
3443       history  for  the  next  entry matching the search string typed so far.
3444       Any other key sequence bound to a readline command will  terminate  the
3445       search  and  execute that command.  For instance, a newline will termi‐
3446       nate the search and accept the line, thereby executing the command from
3447       the history list.
3448
3449       Readline remembers the last incremental search string.  If two Control-
3450       Rs are typed without any intervening characters defining a  new  search
3451       string, any remembered search string is used.
3452
3453       Non-incremental  searches read the entire search string before starting
3454       to search for matching history lines.  The search string may  be  typed
3455       by the user or be part of the contents of the current line.
3456
3457   Readline Command Names
3458       The  following  is  a list of the names of the commands and the default
3459       key sequences to which they are bound.  Command names without an accom‐
3460       panying key sequence are unbound by default.  In the following descrip‐
3461       tions, point refers to the current cursor position, and mark refers  to
3462       a  cursor position saved by the set-mark command.  The text between the
3463       point and mark is referred to as the region.
3464
3465   Commands for Moving
3466       beginning-of-line (C-a)
3467              Move to the start of the current line.
3468       end-of-line (C-e)
3469              Move to the end of the line.
3470       forward-char (C-f)
3471              Move forward a character.
3472       backward-char (C-b)
3473              Move back a character.
3474       forward-word (M-f)
3475              Move forward to the end of the next word.  Words are composed of
3476              alphanumeric characters (letters and digits).
3477       backward-word (M-b)
3478              Move  back  to the start of the current or previous word.  Words
3479              are composed of alphanumeric characters (letters and digits).
3480       shell-forward-word
3481              Move forward to the end of the next word.  Words  are  delimited
3482              by non-quoted shell metacharacters.
3483       shell-backward-word
3484              Move  back  to the start of the current or previous word.  Words
3485              are delimited by non-quoted shell metacharacters.
3486       previous-screen-line
3487              Attempt to move point to the same physical screen column on  the
3488              previous  physical  screen  line. This will not have the desired
3489              effect if the current Readline line does not take up  more  than
3490              one  physical line or if point is not greater than the length of
3491              the prompt plus the screen width.
3492       next-screen-line
3493              Attempt to move point to the same physical screen column on  the
3494              next physical screen line. This will not have the desired effect
3495              if the current Readline line does not  take  up  more  than  one
3496              physical  line  or if the length of the current Readline line is
3497              not greater than the length of the prompt plus the screen width.
3498       clear-screen (C-l)
3499              Clear the screen leaving the current line  at  the  top  of  the
3500              screen.   With  an  argument,  refresh  the current line without
3501              clearing the screen.
3502       redraw-current-line
3503              Refresh the current line.
3504
3505   Commands for Manipulating the History
3506       accept-line (Newline, Return)
3507              Accept the line regardless of where the cursor is.  If this line
3508              is  non-empty, add it to the history list according to the state
3509              of the HISTCONTROL variable.  If the line is a modified  history
3510              line, then restore the history line to its original state.
3511       previous-history (C-p)
3512              Fetch the previous command from the history list, moving back in
3513              the list.
3514       next-history (C-n)
3515              Fetch the next command from the history list, moving forward  in
3516              the list.
3517       beginning-of-history (M-<)
3518              Move to the first line in the history.
3519       end-of-history (M->)
3520              Move  to  the end of the input history, i.e., the line currently
3521              being entered.
3522       reverse-search-history (C-r)
3523              Search backward starting at the current  line  and  moving  `up'
3524              through  the  history  as  necessary.   This  is  an incremental
3525              search.
3526       forward-search-history (C-s)
3527              Search forward starting at the current line  and  moving  `down'
3528              through  the  history  as  necessary.   This  is  an incremental
3529              search.
3530       non-incremental-reverse-search-history (M-p)
3531              Search backward through the history starting at the current line
3532              using  a  non-incremental  search  for  a string supplied by the
3533              user.
3534       non-incremental-forward-search-history (M-n)
3535              Search forward  through  the  history  using  a  non-incremental
3536              search for a string supplied by the user.
3537       history-search-forward
3538              Search  forward through the history for the string of characters
3539              between the start of the current line and the point.  This is  a
3540              non-incremental search.
3541       history-search-backward
3542              Search backward through the history for the string of characters
3543              between the start of the current line and the point.  This is  a
3544              non-incremental search.
3545       history-substring-search-backward
3546              Search backward through the history for the string of characters
3547              between the start of the current line  and  the  current  cursor
3548              position (the point).  The search string may match anywhere in a
3549              history line.  This is a non-incremental search.
3550       history-substring-search-forward
3551              Search forward through the history for the string of  characters
3552              between the start of the current line and the point.  The search
3553              string may match anywhere in a history line.   This  is  a  non-
3554              incremental search.
3555       yank-nth-arg (M-C-y)
3556              Insert  the  first argument to the previous command (usually the
3557              second word on the previous line) at point.  With an argument n,
3558              insert  the nth word from the previous command (the words in the
3559              previous command  begin  with  word  0).   A  negative  argument
3560              inserts the nth word from the end of the previous command.  Once
3561              the argument n is computed, the argument is extracted as if  the
3562              "!n" history expansion had been specified.
3563       yank-last-arg (M-., M-_)
3564              Insert  the last argument to the previous command (the last word
3565              of the previous history entry).  With a numeric argument, behave
3566              exactly  like  yank-nth-arg.   Successive calls to yank-last-arg
3567              move back through the history list, inserting the last word  (or
3568              the  word  specified  by the argument to the first call) of each
3569              line in turn.  Any numeric argument supplied to these successive
3570              calls  determines  the direction to move through the history.  A
3571              negative argument switches the  direction  through  the  history
3572              (back or forward).  The history expansion facilities are used to
3573              extract the last word, as if the "!$" history expansion had been
3574              specified.
3575       shell-expand-line (M-C-e)
3576              Expand the line as the shell does.  This performs alias and his‐
3577              tory expansion as well as all of the shell word expansions.  See
3578              HISTORY EXPANSION below for a description of history expansion.
3579       history-expand-line (M-^)
3580              Perform  history  expansion  on  the  current line.  See HISTORY
3581              EXPANSION below for a description of history expansion.
3582       magic-space
3583              Perform history expansion on  the  current  line  and  insert  a
3584              space.  See HISTORY EXPANSION below for a description of history
3585              expansion.
3586       alias-expand-line
3587              Perform alias expansion on the current line.  See ALIASES  above
3588              for a description of alias expansion.
3589       history-and-alias-expand-line
3590              Perform history and alias expansion on the current line.
3591       insert-last-argument (M-., M-_)
3592              A synonym for yank-last-arg.
3593       operate-and-get-next (C-o)
3594              Accept  the  current  line for execution and fetch the next line
3595              relative to the current line from the history  for  editing.   A
3596              numeric  argument,  if  supplied, specifies the history entry to
3597              use instead of the current line.
3598       edit-and-execute-command (C-x C-e)
3599              Invoke an editor on the current command line,  and  execute  the
3600              result  as  shell  commands.   Bash  attempts to invoke $VISUAL,
3601              $EDITOR, and emacs as the editor, in that order.
3602
3603   Commands for Changing Text
3604       end-of-file (usually C-d)
3605              The character indicating end-of-file as  set,  for  example,  by
3606              ``stty''.   If  this character is read when there are no charac‐
3607              ters on the line, and point is at the  beginning  of  the  line,
3608              Readline interprets it as the end of input and returns EOF.
3609       delete-char (C-d)
3610              Delete the character at point.  If this function is bound to the
3611              same character as the tty EOF character, as C-d commonly is, see
3612              above for the effects.
3613       backward-delete-char (Rubout)
3614              Delete  the  character  behind the cursor.  When given a numeric
3615              argument, save the deleted text on the kill ring.
3616       forward-backward-delete-char
3617              Delete the character under the cursor, unless the cursor  is  at
3618              the end of the line, in which case the character behind the cur‐
3619              sor is deleted.
3620       quoted-insert (C-q, C-v)
3621              Add the next character typed to the line verbatim.  This is  how
3622              to insert characters like C-q, for example.
3623       tab-insert (C-v TAB)
3624              Insert a tab character.
3625       self-insert (a, b, A, 1, !, ...)
3626              Insert the character typed.
3627       transpose-chars (C-t)
3628              Drag  the  character  before point forward over the character at
3629              point, moving point forward as well.  If point is at the end  of
3630              the  line, then this transposes the two characters before point.
3631              Negative arguments have no effect.
3632       transpose-words (M-t)
3633              Drag the word before point past the  word  after  point,  moving
3634              point  over  that  word  as well.  If point is at the end of the
3635              line, this transposes the last two words on the line.
3636       upcase-word (M-u)
3637              Uppercase the current (or  following)  word.   With  a  negative
3638              argument, uppercase the previous word, but do not move point.
3639       downcase-word (M-l)
3640              Lowercase  the  current  (or  following)  word.  With a negative
3641              argument, lowercase the previous word, but do not move point.
3642       capitalize-word (M-c)
3643              Capitalize the current (or following)  word.   With  a  negative
3644              argument, capitalize the previous word, but do not move point.
3645       overwrite-mode
3646              Toggle  overwrite mode.  With an explicit positive numeric argu‐
3647              ment, switches to overwrite mode.  With an explicit non-positive
3648              numeric argument, switches to insert mode.  This command affects
3649              only emacs mode; vi mode does overwrite differently.  Each  call
3650              to readline() starts in insert mode.  In overwrite mode, charac‐
3651              ters bound to self-insert replace the text at point rather  than
3652              pushing  the  text  to  the  right.   Characters  bound to back‐
3653              ward-delete-char replace  the  character  before  point  with  a
3654              space.  By default, this command is unbound.
3655
3656   Killing and Yanking
3657       kill-line (C-k)
3658              Kill the text from point to the end of the line.
3659       backward-kill-line (C-x Rubout)
3660              Kill backward to the beginning of the line.
3661       unix-line-discard (C-u)
3662              Kill  backward  from  point  to  the beginning of the line.  The
3663              killed text is saved on the kill-ring.
3664       kill-whole-line
3665              Kill all characters on the current line, no matter  where  point
3666              is.
3667       kill-word (M-d)
3668              Kill  from  point  to the end of the current word, or if between
3669              words, to the end of the next word.   Word  boundaries  are  the
3670              same as those used by forward-word.
3671       backward-kill-word (M-Rubout)
3672              Kill  the  word  behind  point.  Word boundaries are the same as
3673              those used by backward-word.
3674       shell-kill-word
3675              Kill from point to the end of the current word,  or  if  between
3676              words,  to  the  end  of the next word.  Word boundaries are the
3677              same as those used by shell-forward-word.
3678       shell-backward-kill-word
3679              Kill the word behind point.  Word boundaries  are  the  same  as
3680              those used by shell-backward-word.
3681       unix-word-rubout (C-w)
3682              Kill  the  word behind point, using white space as a word bound‐
3683              ary.  The killed text is saved on the kill-ring.
3684       unix-filename-rubout
3685              Kill the word behind point, using  white  space  and  the  slash
3686              character  as  the word boundaries.  The killed text is saved on
3687              the kill-ring.
3688       delete-horizontal-space (M-\)
3689              Delete all spaces and tabs around point.
3690       kill-region
3691              Kill the text in the current region.
3692       copy-region-as-kill
3693              Copy the text in the region to the kill buffer.
3694       copy-backward-word
3695              Copy the word before point to the kill buffer.  The word  bound‐
3696              aries are the same as backward-word.
3697       copy-forward-word
3698              Copy  the  word  following  point  to the kill buffer.  The word
3699              boundaries are the same as forward-word.
3700       yank (C-y)
3701              Yank the top of the kill ring into the buffer at point.
3702       yank-pop (M-y)
3703              Rotate the kill ring, and yank the new top.  Only works  follow‐
3704              ing yank or yank-pop.
3705
3706   Numeric Arguments
3707       digit-argument (M-0, M-1, ..., M--)
3708              Add  this digit to the argument already accumulating, or start a
3709              new argument.  M-- starts a negative argument.
3710       universal-argument
3711              This is another way to specify an argument.  If this command  is
3712              followed  by one or more digits, optionally with a leading minus
3713              sign, those digits define the argument.  If the command is  fol‐
3714              lowed  by  digits,  executing  universal-argument again ends the
3715              numeric argument, but is otherwise ignored.  As a special  case,
3716              if  this  command is immediately followed by a character that is
3717              neither a digit nor minus sign, the argument count for the  next
3718              command  is multiplied by four.  The argument count is initially
3719              one, so executing this function the first time makes  the  argu‐
3720              ment count four, a second time makes the argument count sixteen,
3721              and so on.
3722
3723   Completing
3724       complete (TAB)
3725              Attempt to perform completion on the text  before  point.   Bash
3726              attempts completion treating the text as a variable (if the text
3727              begins with $), username (if the text begins with  ~),  hostname
3728              (if  the  text begins with @), or command (including aliases and
3729              functions) in turn.  If none of these produces a match, filename
3730              completion is attempted.
3731       possible-completions (M-?)
3732              List the possible completions of the text before point.
3733       insert-completions (M-*)
3734              Insert  all completions of the text before point that would have
3735              been generated by possible-completions.
3736       menu-complete
3737              Similar to complete, but replaces the word to be completed  with
3738              a  single match from the list of possible completions.  Repeated
3739              execution of menu-complete steps through the  list  of  possible
3740              completions,  inserting  each  match in turn.  At the end of the
3741              list of completions, the bell is rung (subject to the setting of
3742              bell-style) and the original text is restored.  An argument of n
3743              moves n positions forward in the list  of  matches;  a  negative
3744              argument  may  be  used to move backward through the list.  This
3745              command is intended to be  bound  to  TAB,  but  is  unbound  by
3746              default.
3747       menu-complete-backward
3748              Identical  to menu-complete, but moves backward through the list
3749              of possible completions, as if menu-complete had  been  given  a
3750              negative argument.  This command is unbound by default.
3751       delete-char-or-list
3752              Deletes  the  character under the cursor if not at the beginning
3753              or end of the line (like delete-char).  If at  the  end  of  the
3754              line, behaves identically to possible-completions.  This command
3755              is unbound by default.
3756       complete-filename (M-/)
3757              Attempt filename completion on the text before point.
3758       possible-filename-completions (C-x /)
3759              List the possible completions of the text before point, treating
3760              it as a filename.
3761       complete-username (M-~)
3762              Attempt  completion  on  the text before point, treating it as a
3763              username.
3764       possible-username-completions (C-x ~)
3765              List the possible completions of the text before point, treating
3766              it as a username.
3767       complete-variable (M-$)
3768              Attempt  completion  on  the text before point, treating it as a
3769              shell variable.
3770       possible-variable-completions (C-x $)
3771              List the possible completions of the text before point, treating
3772              it as a shell variable.
3773       complete-hostname (M-@)
3774              Attempt  completion  on  the text before point, treating it as a
3775              hostname.
3776       possible-hostname-completions (C-x @)
3777              List the possible completions of the text before point, treating
3778              it as a hostname.
3779       complete-command (M-!)
3780              Attempt  completion  on  the text before point, treating it as a
3781              command name.  Command completion attempts  to  match  the  text
3782              against   aliases,   reserved   words,  shell  functions,  shell
3783              builtins, and finally executable filenames, in that order.
3784       possible-command-completions (C-x !)
3785              List the possible completions of the text before point, treating
3786              it as a command name.
3787       dynamic-complete-history (M-TAB)
3788              Attempt  completion on the text before point, comparing the text
3789              against lines from the  history  list  for  possible  completion
3790              matches.
3791       dabbrev-expand
3792              Attempt  menu completion on the text before point, comparing the
3793              text against lines from the history list for possible completion
3794              matches.
3795       complete-into-braces (M-{)
3796              Perform filename completion and insert the list of possible com‐
3797              pletions enclosed within braces so the list is available to  the
3798              shell (see Brace Expansion above).
3799
3800   Keyboard Macros
3801       start-kbd-macro (C-x ()
3802              Begin  saving  the  characters  typed  into the current keyboard
3803              macro.
3804       end-kbd-macro (C-x ))
3805              Stop saving the characters typed into the current keyboard macro
3806              and store the definition.
3807       call-last-kbd-macro (C-x e)
3808              Re-execute  the last keyboard macro defined, by making the char‐
3809              acters in the macro appear as if typed at the keyboard.
3810       print-last-kbd-macro ()
3811              Print the last keyboard macro defined in a format  suitable  for
3812              the inputrc file.
3813
3814   Miscellaneous
3815       re-read-init-file (C-x C-r)
3816              Read  in  the  contents of the inputrc file, and incorporate any
3817              bindings or variable assignments found there.
3818       abort (C-g)
3819              Abort the current editing command and ring the  terminal's  bell
3820              (subject to the setting of bell-style).
3821       do-lowercase-version (M-A, M-B, M-x, ...)
3822              If  the  metafied character x is uppercase, run the command that
3823              is bound to the corresponding metafied lowercase character.  The
3824              behavior is undefined if x is already lowercase.
3825       prefix-meta (ESC)
3826              Metafy the next character typed.  ESC f is equivalent to Meta-f.
3827       undo (C-_, C-x C-u)
3828              Incremental undo, separately remembered for each line.
3829       revert-line (M-r)
3830              Undo  all changes made to this line.  This is like executing the
3831              undo command enough times to return  the  line  to  its  initial
3832              state.
3833       tilde-expand (M-&)
3834              Perform tilde expansion on the current word.
3835       set-mark (C-@, M-<space>)
3836              Set  the  mark to the point.  If a numeric argument is supplied,
3837              the mark is set to that position.
3838       exchange-point-and-mark (C-x C-x)
3839              Swap the point with the mark.  The current  cursor  position  is
3840              set  to the saved position, and the old cursor position is saved
3841              as the mark.
3842       character-search (C-])
3843              A character is read and point is moved to the next occurrence of
3844              that  character.   A negative count searches for previous occur‐
3845              rences.
3846       character-search-backward (M-C-])
3847              A character is read and point is moved to  the  previous  occur‐
3848              rence  of  that character.  A negative count searches for subse‐
3849              quent occurrences.
3850       skip-csi-sequence
3851              Read enough characters to consume a multi-key sequence  such  as
3852              those  defined for keys like Home and End.  Such sequences begin
3853              with a Control Sequence Indicator (CSI), usually ESC-[.  If this
3854              sequence  is  bound  to "\[", keys producing such sequences will
3855              have no effect unless explicitly bound to  a  readline  command,
3856              instead  of  inserting stray characters into the editing buffer.
3857              This is unbound by default, but usually bound to ESC-[.
3858       insert-comment (M-#)
3859              Without a numeric argument,  the  value  of  the  readline  com‐
3860              ment-begin  variable is inserted at the beginning of the current
3861              line.  If a numeric argument is supplied, this command acts as a
3862              toggle:  if  the  characters at the beginning of the line do not
3863              match the value of comment-begin, the value is inserted,  other‐
3864              wise the characters in comment-begin are deleted from the begin‐
3865              ning of the line.  In either case, the line is accepted as if  a
3866              newline  had  been  typed.   The  default value of comment-begin
3867              causes this command to make the current line  a  shell  comment.
3868              If  a  numeric  argument  causes  the  comment  character  to be
3869              removed, the line will be executed by the shell.
3870       glob-complete-word (M-g)
3871              The word before point is  treated  as  a  pattern  for  pathname
3872              expansion,  with  an asterisk implicitly appended.  This pattern
3873              is used to generate a list of matching  filenames  for  possible
3874              completions.
3875       glob-expand-word (C-x *)
3876              The  word  before  point  is  treated  as a pattern for pathname
3877              expansion, and the  list  of  matching  filenames  is  inserted,
3878              replacing  the  word.   If  a  numeric  argument is supplied, an
3879              asterisk is appended before pathname expansion.
3880       glob-list-expansions (C-x g)
3881              The list  of  expansions  that  would  have  been  generated  by
3882              glob-expand-word  is  displayed,  and the line is redrawn.  If a
3883              numeric argument is supplied, an  asterisk  is  appended  before
3884              pathname expansion.
3885       dump-functions
3886              Print  all  of the functions and their key bindings to the read‐
3887              line output stream.  If a numeric argument is supplied, the out‐
3888              put  is  formatted  in such a way that it can be made part of an
3889              inputrc file.
3890       dump-variables
3891              Print all of the settable readline variables and their values to
3892              the  readline output stream.  If a numeric argument is supplied,
3893              the output is formatted in such a way that it can be  made  part
3894              of an inputrc file.
3895       dump-macros
3896              Print  all of the readline key sequences bound to macros and the
3897              strings they output.  If a numeric  argument  is  supplied,  the
3898              output is formatted in such a way that it can be made part of an
3899              inputrc file.
3900       display-shell-version (C-x C-v)
3901              Display version information about the current instance of bash.
3902
3903   Programmable Completion
3904       When word completion is attempted for an  argument  to  a  command  for
3905       which  a  completion  specification (a compspec) has been defined using
3906       the complete builtin (see SHELL BUILTIN COMMANDS below),  the  program‐
3907       mable completion facilities are invoked.
3908
3909       First,  the  command  name  is  identified.  If the command word is the
3910       empty string (completion attempted at the beginning of an empty  line),
3911       any  compspec  defined  with  the  -E option to complete is used.  If a
3912       compspec has been defined for that command, the  compspec  is  used  to
3913       generate the list of possible completions for the word.  If the command
3914       word is a full pathname, a compspec for the full pathname  is  searched
3915       for  first.   If no compspec is found for the full pathname, an attempt
3916       is made to find a compspec for the portion following the  final  slash.
3917       If  those  searches  do  not result in a compspec, any compspec defined
3918       with the -D option to complete is used as the default.  If there is  no
3919       default  compspec, bash attempts alias expansion on the command word as
3920       a final resort, and attempts to find a compspec for  the  command  word
3921       from any successful expansion.
3922
3923       Once  a  compspec  has  been  found, it is used to generate the list of
3924       matching words.  If a compspec is not found, the default  bash  comple‐
3925       tion as described above under Completing is performed.
3926
3927       First,  the  actions  specified by the compspec are used.  Only matches
3928       which are prefixed by the word being completed are returned.  When  the
3929       -f  or -d option is used for filename or directory name completion, the
3930       shell variable FIGNORE is used to filter the matches.
3931
3932       Any completions specified by a pathname expansion  pattern  to  the  -G
3933       option are generated next.  The words generated by the pattern need not
3934       match the word being completed.  The GLOBIGNORE shell variable  is  not
3935       used to filter the matches, but the FIGNORE variable is used.
3936
3937       Next,  the string specified as the argument to the -W option is consid‐
3938       ered.  The string is first split using the characters in the  IFS  spe‐
3939       cial  variable  as delimiters.  Shell quoting is honored.  Each word is
3940       then expanded using brace expansion,  tilde  expansion,  parameter  and
3941       variable  expansion, command substitution, and arithmetic expansion, as
3942       described above under EXPANSION.  The results are split using the rules
3943       described above under Word Splitting.  The results of the expansion are
3944       prefix-matched against the word being completed, and the matching words
3945       become the possible completions.
3946
3947       After  these matches have been generated, any shell function or command
3948       specified with the -F and -C options is invoked.  When the  command  or
3949       function is invoked, the COMP_LINE, COMP_POINT, COMP_KEY, and COMP_TYPE
3950       variables are assigned values as described above under Shell Variables.
3951       If  a  shell  function  is being invoked, the COMP_WORDS and COMP_CWORD
3952       variables are also set.  When the function or command is  invoked,  the
3953       first  argument  ($1)  is  the  name of the command whose arguments are
3954       being completed, the second argument ($2) is the word being  completed,
3955       and  the  third argument ($3) is the word preceding the word being com‐
3956       pleted on the current command line.  No filtering of the generated com‐
3957       pletions against the word being completed is performed; the function or
3958       command has complete freedom in generating the matches.
3959
3960       Any function specified with -F is invoked first.  The function may  use
3961       any  of  the  shell facilities, including the compgen builtin described
3962       below, to generate the matches.  It must put the  possible  completions
3963       in the COMPREPLY array variable, one per array element.
3964
3965       Next,  any  command specified with the -C option is invoked in an envi‐
3966       ronment equivalent to command substitution.  It should print a list  of
3967       completions,  one  per  line, to the standard output.  Backslash may be
3968       used to escape a newline, if necessary.
3969
3970       After all of the possible completions are generated, any filter  speci‐
3971       fied  with  the -X option is applied to the list.  The filter is a pat‐
3972       tern as used for pathname expansion; a & in  the  pattern  is  replaced
3973       with  the text of the word being completed.  A literal & may be escaped
3974       with a backslash; the backslash is removed before attempting  a  match.
3975       Any  completion that matches the pattern will be removed from the list.
3976       A leading ! negates the pattern; in this case any completion not match‐
3977       ing  the  pattern  will be removed.  If the nocasematch shell option is
3978       enabled, the match is performed without regard to the  case  of  alpha‐
3979       betic characters.
3980
3981       Finally, any prefix and suffix specified with the -P and -S options are
3982       added to each member of the completion list, and the result is returned
3983       to the readline completion code as the list of possible completions.
3984
3985       If  the previously-applied actions do not generate any matches, and the
3986       -o dirnames option was supplied  to  complete  when  the  compspec  was
3987       defined, directory name completion is attempted.
3988
3989       If  the  -o  plusdirs option was supplied to complete when the compspec
3990       was defined, directory name completion is attempted and any matches are
3991       added to the results of the other actions.
3992
3993       By  default,  if a compspec is found, whatever it generates is returned
3994       to the completion code as the full set of  possible  completions.   The
3995       default bash completions are not attempted, and the readline default of
3996       filename completion is disabled.  If the -o bashdefault option was sup‐
3997       plied  to complete when the compspec was defined, the bash default com‐
3998       pletions are attempted if the compspec generates no matches.  If the -o
3999       default  option was supplied to complete when the compspec was defined,
4000       readline's default completion will be performed if the  compspec  (and,
4001       if attempted, the default bash completions) generate no matches.
4002
4003       When  a  compspec  indicates that directory name completion is desired,
4004       the programmable completion functions force readline to append a  slash
4005       to  completed names which are symbolic links to directories, subject to
4006       the value of the mark-directories readline variable, regardless of  the
4007       setting of the mark-symlinked-directories readline variable.
4008
4009       There  is  some support for dynamically modifying completions.  This is
4010       most useful when used in combination with a default  completion  speci‐
4011       fied  with  complete -D.  It's possible for shell functions executed as
4012       completion handlers to indicate that completion should  be  retried  by
4013       returning  an exit status of 124.  If a shell function returns 124, and
4014       changes the compspec associated with the command on which completion is
4015       being  attempted  (supplied  as the first argument when the function is
4016       executed), programmable completion restarts from the beginning, with an
4017       attempt  to find a new compspec for that command.  This allows a set of
4018       completions to be built dynamically as completion is attempted,  rather
4019       than being loaded all at once.
4020
4021       For  instance, assuming that there is a library of compspecs, each kept
4022       in a file corresponding to the  name  of  the  command,  the  following
4023       default completion function would load completions dynamically:
4024
4025       _completion_loader()
4026       {
4027            . "/etc/bash_completion.d/$1.sh" >/dev/null 2>&1 && return 124
4028       }
4029       complete -D -F _completion_loader -o bashdefault -o default
4030
4031

HISTORY

4033       When  the  -o  history  option to the set builtin is enabled, the shell
4034       provides access to the command history, the list of commands previously
4035       typed.   The  value  of  the HISTSIZE variable is used as the number of
4036       commands to save in a history list.  The text of the last HISTSIZE com‐
4037       mands  (default  500)  is  saved.  The shell stores each command in the
4038       history list prior to parameter and variable expansion  (see  EXPANSION
4039       above)  but after history expansion is performed, subject to the values
4040       of the shell variables HISTIGNORE and HISTCONTROL.
4041
4042       On startup, the history is initialized from the file named by the vari‐
4043       able  HISTFILE  (default ~/.bash_history).  The file named by the value
4044       of HISTFILE is truncated, if necessary, to contain  no  more  than  the
4045       number  of  lines specified by the value of HISTFILESIZE.  If HISTFILE‐
4046       SIZE is unset, or set to null, a non-numeric value, or a numeric  value
4047       less  than  zero,  the history file is not truncated.  When the history
4048       file is read, lines beginning with the history comment  character  fol‐
4049       lowed immediately by a digit are interpreted as timestamps for the fol‐
4050       lowing history line.  These timestamps are optionally displayed depend‐
4051       ing  on  the  value  of the HISTTIMEFORMAT variable.  When a shell with
4052       history enabled exits, the last $HISTSIZE lines  are  copied  from  the
4053       history  list  to $HISTFILE.  If the histappend shell option is enabled
4054       (see the description of shopt under SHELL BUILTIN COMMANDS below),  the
4055       lines  are  appended to the history file, otherwise the history file is
4056       overwritten.   If  HISTFILE  is  unset,  or  if  the  history  file  is
4057       unwritable,  the  history is not saved.  If the HISTTIMEFORMAT variable
4058       is set, time stamps are written to the history file,  marked  with  the
4059       history  comment  character, so they may be preserved across shell ses‐
4060       sions.  This uses the history comment character  to  distinguish  time‐
4061       stamps from other history lines.  After saving the history, the history
4062       file is truncated to contain no more than HISTFILESIZE lines.  If HIST‐
4063       FILESIZE  is  unset,  or set to null, a non-numeric value, or a numeric
4064       value less than zero, the history file is not truncated.
4065
4066       The builtin command fc (see SHELL BUILTIN COMMANDS below) may  be  used
4067       to list or edit and re-execute a portion of the history list.  The his‐
4068       tory builtin may be used to display or  modify  the  history  list  and
4069       manipulate  the  history file.  When using command-line editing, search
4070       commands are available in each editing mode that provide access to  the
4071       history list.
4072
4073       The  shell  allows control over which commands are saved on the history
4074       list.  The HISTCONTROL and HISTIGNORE variables may be set to cause the
4075       shell to save only a subset of the commands entered.  The cmdhist shell
4076       option, if enabled, causes the shell to attempt to save each line of  a
4077       multi-line  command  in the same history entry, adding semicolons where
4078       necessary to preserve syntactic correctness.  The lithist shell  option
4079       causes  the shell to save the command with embedded newlines instead of
4080       semicolons.  See the description of the shopt builtin below under SHELL
4081       BUILTIN  COMMANDS  for  information  on  setting  and  unsetting  shell
4082       options.
4083

HISTORY EXPANSION

4085       The shell supports a history expansion feature that is similar  to  the
4086       history  expansion in csh.  This section describes what syntax features
4087       are available.  This feature is  enabled  by  default  for  interactive
4088       shells, and can be disabled using the +H option to the set builtin com‐
4089       mand (see SHELL BUILTIN COMMANDS below).  Non-interactive shells do not
4090       perform history expansion by default.
4091
4092       History expansions introduce words from the history list into the input
4093       stream, making it easy to repeat commands, insert the  arguments  to  a
4094       previous command into the current input line, or fix errors in previous
4095       commands quickly.
4096
4097       History expansion is performed immediately after  a  complete  line  is
4098       read,  before  the shell breaks it into words, and is performed on each
4099       line  individually  without  taking  quoting  on  previous  lines  into
4100       account.  It takes place in two parts.  The first is to determine which
4101       line from the history list to use during substitution.  The  second  is
4102       to  select  portions  of  that line for inclusion into the current one.
4103       The line selected from the history is the event, and  the  portions  of
4104       that  line that are acted upon are words.  Various modifiers are avail‐
4105       able to manipulate the selected words.  The line is broken  into  words
4106       in  the same fashion as when reading input, so that several metacharac‐
4107       ter-separated words surrounded by quotes are considered one word.  His‐
4108       tory  expansions are introduced by the appearance of the history expan‐
4109       sion character, which is ! by default.  Only backslash (\)  and  single
4110       quotes  can  quote  the  history  expansion  character, but the history
4111       expansion character is also treated as quoted if  it  immediately  pre‐
4112       cedes the closing double quote in a double-quoted string.
4113
4114       Several  characters inhibit history expansion if found immediately fol‐
4115       lowing the history expansion character, even if it is unquoted:  space,
4116       tab,  newline,  carriage return, and =.  If the extglob shell option is
4117       enabled, ( will also inhibit expansion.
4118
4119       Several shell options settable with the shopt builtin may  be  used  to
4120       tailor  the  behavior  of  history  expansion.  If the histverify shell
4121       option is enabled (see the description of the shopt builtin below), and
4122       readline  is  being  used,  history  substitutions  are not immediately
4123       passed to the shell parser.  Instead, the  expanded  line  is  reloaded
4124       into the readline editing buffer for further modification.  If readline
4125       is being used, and the histreedit shell option  is  enabled,  a  failed
4126       history  substitution will be reloaded into the readline editing buffer
4127       for correction.  The -p option to the history builtin  command  may  be
4128       used  to  see what a history expansion will do before using it.  The -s
4129       option to the history builtin may be used to add commands to the end of
4130       the  history  list  without  actually  executing them, so that they are
4131       available for subsequent recall.
4132
4133       The shell allows control of the various characters used by the  history
4134       expansion mechanism (see the description of histchars above under Shell
4135       Variables).  The shell uses the history comment character to mark  his‐
4136       tory timestamps when writing the history file.
4137
4138   Event Designators
4139       An  event designator is a reference to a command line entry in the his‐
4140       tory list.  Unless the reference is absolute, events  are  relative  to
4141       the current position in the history list.
4142
4143       !      Start  a  history substitution, except when followed by a blank,
4144              newline, carriage return, = or ( (when the extglob shell  option
4145              is enabled using the shopt builtin).
4146       !n     Refer to command line n.
4147       !-n    Refer to the current command minus n.
4148       !!     Refer to the previous command.  This is a synonym for `!-1'.
4149       !string
4150              Refer  to the most recent command preceding the current position
4151              in the history list starting with string.
4152       !?string[?]
4153              Refer to the most recent command preceding the current  position
4154              in  the  history  list containing string.  The trailing ? may be
4155              omitted if string is followed immediately by a newline.
4156       ^string1^string2^
4157              Quick substitution.   Repeat  the  previous  command,  replacing
4158              string1  with  string2.  Equivalent to ``!!:s/string1/string2/''
4159              (see Modifiers below).
4160       !#     The entire command line typed so far.
4161
4162   Word Designators
4163       Word designators are used to select desired words from the event.  A  :
4164       separates  the event specification from the word designator.  It may be
4165       omitted if the word designator begins with a ^, $, *, -, or  %.   Words
4166       are  numbered from the beginning of the line, with the first word being
4167       denoted by 0 (zero).  Words are inserted into the  current  line  sepa‐
4168       rated by single spaces.
4169
4170       0 (zero)
4171              The zeroth word.  For the shell, this is the command word.
4172       n      The nth word.
4173       ^      The first argument.  That is, word 1.
4174       $      The  last  word.   This  is  usually the last argument, but will
4175              expand to the zeroth word if there is only one word in the line.
4176       %      The word matched by the most recent `?string?' search.
4177       x-y    A range of words; `-y' abbreviates `0-y'.
4178       *      All of the words but the zeroth.  This is a synonym  for  `1-$'.
4179              It  is  not  an  error to use * if there is just one word in the
4180              event; the empty string is returned in that case.
4181       x*     Abbreviates x-$.
4182       x-     Abbreviates x-$ like x*, but omits the last word.
4183
4184       If a word designator is supplied without an  event  specification,  the
4185       previous command is used as the event.
4186
4187   Modifiers
4188       After  the optional word designator, there may appear a sequence of one
4189       or more of the following modifiers, each preceded by a `:'.
4190
4191       h      Remove a trailing filename component, leaving only the head.
4192       t      Remove all leading filename components, leaving the tail.
4193       r      Remove a trailing suffix of the form .xxx, leaving the basename.
4194       e      Remove all but the trailing suffix.
4195       p      Print the new command but do not execute it.
4196       q      Quote the substituted words, escaping further substitutions.
4197       x      Quote the substituted words as with q, but break into  words  at
4198              blanks and newlines.
4199       s/old/new/
4200              Substitute  new  for  the  first  occurrence of old in the event
4201              line.  Any delimiter can be used  in  place  of  /.   The  final
4202              delimiter  is  optional if it is the last character of the event
4203              line.  The delimiter may be quoted in old and new with a  single
4204              backslash.   If & appears in new, it is replaced by old.  A sin‐
4205              gle backslash will quote the &.  If old is null, it  is  set  to
4206              the  last  old substituted, or, if no previous history substitu‐
4207              tions took place, the last string in a !?string[?]  search.
4208       &      Repeat the previous substitution.
4209       g      Cause changes to be applied over the entire event line.  This is
4210              used  in  conjunction  with `:s' (e.g., `:gs/old/new/') or `:&'.
4211              If used with `:s', any delimiter can be used in place of /,  and
4212              the  final  delimiter is optional if it is the last character of
4213              the event line.  An a may be used as a synonym for g.
4214       G      Apply the following `s' modifier once to each word in the  event
4215              line.
4216

SHELL BUILTIN COMMANDS

4218       Unless otherwise noted, each builtin command documented in this section
4219       as accepting options preceded by - accepts -- to signify the end of the
4220       options.  The :, true, false, and test/[ builtins do not accept options
4221       and do not treat -- specially.  The exit, logout, return,  break,  con‐
4222       tinue,  let,  and shift builtins accept and process arguments beginning
4223       with - without requiring --.  Other builtins that accept arguments  but
4224       are  not  specified  as accepting options interpret arguments beginning
4225       with - as invalid options and require -- to  prevent  this  interpreta‐
4226       tion.
4227       : [arguments]
4228              No  effect;  the command does nothing beyond expanding arguments
4229              and performing any specified redirections.  The return status is
4230              zero.
4231
4232        .  filename [arguments]
4233       source filename [arguments]
4234              Read  and  execute  commands  from filename in the current shell
4235              environment and return the exit status of the last command  exe‐
4236              cuted  from  filename.   If  filename  does not contain a slash,
4237              filenames in PATH are used  to  find  the  directory  containing
4238              filename.  The file searched for in PATH need not be executable.
4239              When bash is  not  in  posix  mode,  the  current  directory  is
4240              searched  if no file is found in PATH.  If the sourcepath option
4241              to the shopt builtin command is turned  off,  the  PATH  is  not
4242              searched.   If any arguments are supplied, they become the posi‐
4243              tional parameters when  filename  is  executed.   Otherwise  the
4244              positional  parameters  are  unchanged.   If  the  -T  option is
4245              enabled, source inherits any trap on DEBUG; if it  is  not,  any
4246              DEBUG  trap  string  is  saved  and  restored around the call to
4247              source, and source unsets the DEBUG trap while it executes.   If
4248              -T  is not set, and the sourced file changes the DEBUG trap, the
4249              new value is retained when source completes.  The return  status
4250              is the status of the last command exited within the script (0 if
4251              no commands are executed), and false if filename is not found or
4252              cannot be read.
4253
4254       alias [-p] [name[=value] ...]
4255              Alias with no arguments or with the -p option prints the list of
4256              aliases in the form alias name=value on standard  output.   When
4257              arguments  are supplied, an alias is defined for each name whose
4258              value is given.  A trailing space in value causes the next  word
4259              to be checked for alias substitution when the alias is expanded.
4260              For each name in the argument list for which no  value  is  sup‐
4261              plied,  the  name  and  value  of  the  alias is printed.  Alias
4262              returns true unless a name is given for which no alias has  been
4263              defined.
4264
4265       bg [jobspec ...]
4266              Resume  each  suspended  job jobspec in the background, as if it
4267              had been started with &.  If jobspec is not present, the shell's
4268              notion  of the current job is used.  bg jobspec returns 0 unless
4269              run when job control is disabled or, when run with  job  control
4270              enabled,  any  specified  jobspec  was  not found or was started
4271              without job control.
4272
4273       bind [-m keymap] [-lpsvPSVX]
4274       bind [-m keymap] [-q function] [-u function] [-r keyseq]
4275       bind [-m keymap] -f filename
4276       bind [-m keymap] -x keyseq:shell-command
4277       bind [-m keymap] keyseq:function-name
4278       bind [-m keymap] keyseq:readline-command
4279              Display current readline key and function bindings, bind  a  key
4280              sequence  to  a  readline  function  or macro, or set a readline
4281              variable.  Each non-option argument is a  command  as  it  would
4282              appear  in  .inputrc, but each binding or command must be passed
4283              as a separate argument; e.g.,  '"\C-x\C-r":  re-read-init-file'.
4284              Options, if supplied, have the following meanings:
4285              -m keymap
4286                     Use keymap as the keymap to be affected by the subsequent
4287                     bindings.  Acceptable keymap names are emacs, emacs-stan‐
4288                     dard,  emacs-meta,  emacs-ctlx,  vi, vi-move, vi-command,
4289                     and vi-insert.  vi is equivalent to  vi-command  (vi-move
4290                     is  also  a  synonym); emacs is equivalent to emacs-stan‐
4291                     dard.
4292              -l     List the names of all readline functions.
4293              -p     Display readline function names and bindings  in  such  a
4294                     way that they can be re-read.
4295              -P     List current readline function names and bindings.
4296              -s     Display  readline  key  sequences bound to macros and the
4297                     strings they output in such a way that they  can  be  re-
4298                     read.
4299              -S     Display  readline  key  sequences bound to macros and the
4300                     strings they output.
4301              -v     Display readline variable names and values in such a  way
4302                     that they can be re-read.
4303              -V     List current readline variable names and values.
4304              -f filename
4305                     Read key bindings from filename.
4306              -q function
4307                     Query about which keys invoke the named function.
4308              -u function
4309                     Unbind all keys bound to the named function.
4310              -r keyseq
4311                     Remove any current binding for keyseq.
4312              -x keyseq:shell-command
4313                     Cause  shell-command  to  be  executed whenever keyseq is
4314                     entered.  When shell-command is executed, the shell  sets
4315                     the  READLINE_LINE  variable to the contents of the read‐
4316                     line line buffer and the READLINE_POINT variable  to  the
4317                     current location of the insertion point.  If the executed
4318                     command changes  the  value  of  READLINE_LINE  or  READ‐
4319                     LINE_POINT,  those  new  values  will be reflected in the
4320                     editing state.
4321              -X     List all key sequences bound to shell  commands  and  the
4322                     associated  commands  in  a  format that can be reused as
4323                     input.
4324
4325              The return value is 0 unless an unrecognized option is given  or
4326              an error occurred.
4327
4328       break [n]
4329              Exit  from  within a for, while, until, or select loop.  If n is
4330              specified, break n levels.  n must be ≥ 1.  If n is greater than
4331              the  number  of enclosing loops, all enclosing loops are exited.
4332              The return value is 0 unless n is not greater than or  equal  to
4333              1.
4334
4335       builtin shell-builtin [arguments]
4336              Execute  the  specified shell builtin, passing it arguments, and
4337              return its exit status.  This is useful when defining a function
4338              whose  name  is the same as a shell builtin, retaining the func‐
4339              tionality of the builtin within the function.  The cd builtin is
4340              commonly  redefined  this  way.   The  return status is false if
4341              shell-builtin is not a shell builtin command.
4342
4343       caller [expr]
4344              Returns the context of any active subroutine call (a shell func‐
4345              tion or a script executed with the . or source builtins).  With‐
4346              out expr, caller displays the line number and source filename of
4347              the  current subroutine call.  If a non-negative integer is sup‐
4348              plied as expr, caller displays the line number, subroutine name,
4349              and  source  file  corresponding to that position in the current
4350              execution call stack.  This extra information may be  used,  for
4351              example,  to print a stack trace.  The current frame is frame 0.
4352              The return value is 0 unless the shell is not executing  a  sub‐
4353              routine  call or expr does not correspond to a valid position in
4354              the call stack.
4355
4356       cd [-L|[-P [-e]] [-@]] [dir]
4357              Change the current directory to dir.  if dir  is  not  supplied,
4358              the  value of the HOME shell variable is the default.  Any addi‐
4359              tional arguments following dir are ignored.  The variable CDPATH
4360              defines  the  search path for the directory containing dir: each
4361              directory name in  CDPATH  is  searched  for  dir.   Alternative
4362              directory  names in CDPATH are separated by a colon (:).  A null
4363              directory name in CDPATH is the same as the  current  directory,
4364              i.e., ``.''.  If dir begins with a slash (/), then CDPATH is not
4365              used.  The -P option causes cd to  use  the  physical  directory
4366              structure  by  resolving symbolic links while traversing dir and
4367              before processing instances of .. in dir (see also the -P option
4368              to the set builtin command); the -L option forces symbolic links
4369              to be followed by resolving the link after processing  instances
4370              of .. in dir.  If .. appears in dir, it is processed by removing
4371              the immediately previous pathname component from dir, back to  a
4372              slash  or  the  beginning  of dir.  If the -e option is supplied
4373              with -P, and the current working directory  cannot  be  success‐
4374              fully  determined  after  a successful directory change, cd will
4375              return an unsuccessful status.  On systems that support it,  the
4376              -@  option  presents  the  extended attributes associated with a
4377              file as a directory.  An argument of - is converted  to  $OLDPWD
4378              before the directory change is attempted.  If a non-empty direc‐
4379              tory name from CDPATH is used, or if - is  the  first  argument,
4380              and the directory change is successful, the absolute pathname of
4381              the new working directory is written  to  the  standard  output.
4382              The  return  value  is  true  if  the directory was successfully
4383              changed; false otherwise.
4384
4385       command [-pVv] command [arg ...]
4386              Run command with args  suppressing  the  normal  shell  function
4387              lookup.  Only builtin commands or commands found in the PATH are
4388              executed.  If the -p option is given, the search for command  is
4389              performed  using  a default value for PATH that is guaranteed to
4390              find all of the standard utilities.  If  either  the  -V  or  -v
4391              option is supplied, a description of command is printed.  The -v
4392              option causes a single word indicating the command  or  filename
4393              used to invoke command to be displayed; the -V option produces a
4394              more verbose description.  If the -V or -v option  is  supplied,
4395              the  exit  status  is  0 if command was found, and 1 if not.  If
4396              neither option is supplied and an error occurred or command can‐
4397              not  be found, the exit status is 127.  Otherwise, the exit sta‐
4398              tus of the command builtin is the exit status of command.
4399
4400       compgen [option] [word]
4401              Generate possible completion matches for word according  to  the
4402              options,  which  may  be  any  option  accepted  by the complete
4403              builtin with the exception of -p and -r, and write  the  matches
4404              to  the  standard  output.  When using the -F or -C options, the
4405              various shell  variables  set  by  the  programmable  completion
4406              facilities, while available, will not have useful values.
4407
4408              The matches will be generated in the same way as if the program‐
4409              mable completion code had generated them directly from a comple‐
4410              tion  specification  with the same flags.  If word is specified,
4411              only those completions matching word will be displayed.
4412
4413              The return value is true unless an invalid option  is  supplied,
4414              or no matches were generated.
4415
4416       complete  [-abcdefgjksuv] [-o comp-option] [-DEI] [-A action] [-G glob‐
4417       pat] [-W wordlist] [-F function] [-C command]
4418              [-X filterpat] [-P prefix] [-S suffix] name [name ...]
4419       complete -pr [-DEI] [name ...]
4420              Specify how arguments to each name should be completed.  If  the
4421              -p  option  is supplied, or if no options are supplied, existing
4422              completion specifications are printed in a way that allows  them
4423              to be reused as input.  The -r option removes a completion spec‐
4424              ification for each name, or, if no names are supplied, all  com‐
4425              pletion specifications.  The -D option indicates that other sup‐
4426              plied options and actions should apply to the  ``default''  com‐
4427              mand  completion; that is, completion attempted on a command for
4428              which no completion has previously been defined.  The -E  option
4429              indicates  that  other supplied options and actions should apply
4430              to ``empty'' command completion; that is,  completion  attempted
4431              on  a  blank  line.  The -I option indicates that other supplied
4432              options and actions should apply to  completion  on  the  inital
4433              non-assignment  word  on  the line, or after a command delimiter
4434              such as ; or |, which is usually command  name  completion.   If
4435              multiple  options  are  supplied, the -D option takes precedence
4436              over -E, and both take precedence over -I.  If any of -D, -E, or
4437              -I  are  supplied,  any  other name arguments are ignored; these
4438              completions only apply to the case specified by the option.
4439
4440              The process of applying  these  completion  specifications  when
4441              word  completion  is attempted is described above under Program‐
4442              mable Completion.
4443
4444              Other options, if specified, have the following  meanings.   The
4445              arguments  to the -G, -W, and -X options (and, if necessary, the
4446              -P and -S options) should be quoted to protect them from  expan‐
4447              sion before the complete builtin is invoked.
4448              -o comp-option
4449                      The  comp-option  controls  several aspects of the comp‐
4450                      spec's behavior beyond the simple generation of  comple‐
4451                      tions.  comp-option may be one of:
4452                      bashdefault
4453                              Perform the rest of the default bash completions
4454                              if the compspec generates no matches.
4455                      default Use readline's default  filename  completion  if
4456                              the compspec generates no matches.
4457                      dirnames
4458                              Perform  directory  name completion if the comp‐
4459                              spec generates no matches.
4460                      filenames
4461                              Tell readline that the compspec generates  file‐
4462                              names,  so  it can perform any filename-specific
4463                              processing (like adding  a  slash  to  directory
4464                              names,  quoting special characters, or suppress‐
4465                              ing trailing spaces).  Intended to be used  with
4466                              shell functions.
4467                      noquote Tell  readline  not to quote the completed words
4468                              if they are filenames (quoting filenames is  the
4469                              default).
4470                      nosort  Tell  readline  not to sort the list of possible
4471                              completions alphabetically.
4472                      nospace Tell  readline  not  to  append  a  space   (the
4473                              default)  to  words  completed at the end of the
4474                              line.
4475                      plusdirs
4476                              After any matches defined by  the  compspec  are
4477                              generated,    directory   name   completion   is
4478                              attempted and  any  matches  are  added  to  the
4479                              results of the other actions.
4480              -A action
4481                      The  action  may  be  one of the following to generate a
4482                      list of possible completions:
4483                      alias   Alias names.  May also be specified as -a.
4484                      arrayvar
4485                              Array variable names.
4486                      binding Readline key binding names.
4487                      builtin Names of shell builtin commands.   May  also  be
4488                              specified as -b.
4489                      command Command names.  May also be specified as -c.
4490                      directory
4491                              Directory names.  May also be specified as -d.
4492                      disabled
4493                              Names of disabled shell builtins.
4494                      enabled Names of enabled shell builtins.
4495                      export  Names  of exported shell variables.  May also be
4496                              specified as -e.
4497                      file    File names.  May also be specified as -f.
4498                      function
4499                              Names of shell functions.
4500                      group   Group names.  May also be specified as -g.
4501                      helptopic
4502                              Help topics as accepted by the help builtin.
4503                      hostname
4504                              Hostnames, as taken from the file  specified  by
4505                              the HOSTFILE shell variable.
4506                      job     Job  names,  if job control is active.  May also
4507                              be specified as -j.
4508                      keyword Shell reserved words.  May also be specified  as
4509                              -k.
4510                      running Names of running jobs, if job control is active.
4511                      service Service names.  May also be specified as -s.
4512                      setopt  Valid  arguments  for  the  -o option to the set
4513                              builtin.
4514                      shopt   Shell option names  as  accepted  by  the  shopt
4515                              builtin.
4516                      signal  Signal names.
4517                      stopped Names of stopped jobs, if job control is active.
4518                      user    User names.  May also be specified as -u.
4519                      variable
4520                              Names of all shell variables.  May also be spec‐
4521                              ified as -v.
4522              -C command
4523                      command is executed in a subshell environment,  and  its
4524                      output is used as the possible completions.
4525              -F function
4526                      The  shell  function function is executed in the current
4527                      shell environment.  When the function is  executed,  the
4528                      first  argument  ($1)  is  the name of the command whose
4529                      arguments are being completed, the second argument  ($2)
4530                      is the word being completed, and the third argument ($3)
4531                      is the word preceding the word being  completed  on  the
4532                      current  command  line.   When it finishes, the possible
4533                      completions are retrieved from the value of the  COMPRE‐
4534                      PLY array variable.
4535              -G globpat
4536                      The  pathname  expansion  pattern globpat is expanded to
4537                      generate the possible completions.
4538              -P prefix
4539                      prefix is added at the beginning of each  possible  com‐
4540                      pletion after all other options have been applied.
4541              -S suffix
4542                      suffix is appended to each possible completion after all
4543                      other options have been applied.
4544              -W wordlist
4545                      The wordlist is split using the characters  in  the  IFS
4546                      special  variable as delimiters, and each resultant word
4547                      is expanded.  Shell quoting is honored within  wordlist,
4548                      in order to provide a mechanism for the words to contain
4549                      shell metacharacters or characters in the value of  IFS.
4550                      The  possible  completions are the members of the resul‐
4551                      tant list which match the word being completed.
4552              -X filterpat
4553                      filterpat is a pattern as used for  pathname  expansion.
4554                      It is applied to the list of possible completions gener‐
4555                      ated by the preceding options and  arguments,  and  each
4556                      completion  matching filterpat is removed from the list.
4557                      A leading ! in filterpat negates the  pattern;  in  this
4558                      case, any completion not matching filterpat is removed.
4559
4560              The  return  value is true unless an invalid option is supplied,
4561              an option other than -p or -r is supplied without a  name  argu‐
4562              ment,  an  attempt  is made to remove a completion specification
4563              for a name for which no specification exists, or an error occurs
4564              adding a completion specification.
4565
4566       compopt [-o option] [-DEI] [+o option] [name]
4567              Modify  completion  options  for  each  name  according  to  the
4568              options, or for the currently-executing completion if  no  names
4569              are  supplied.   If no options are given, display the completion
4570              options for each name or the current completion.   The  possible
4571              values  of  option  are  those  valid  for  the complete builtin
4572              described above.  The -D option indicates  that  other  supplied
4573              options should apply to the ``default'' command completion; that
4574              is, completion attempted on a command for  which  no  completion
4575              has previously been defined.  The -E option indicates that other
4576              supplied options should apply to ``empty''  command  completion;
4577              that  is,  completion  attempted on a blank line.  The -I option
4578              indicates that other supplied options should apply to completion
4579              on  the  inital non-assignment word on the line, or after a com‐
4580              mand delimiter such as ; or |, which  is  usually  command  name
4581              completion.
4582
4583              The  return  value is true unless an invalid option is supplied,
4584              an attempt is made to modify the options for a name for which no
4585              completion specification exists, or an output error occurs.
4586
4587       continue [n]
4588              Resume the next iteration of the enclosing for, while, until, or
4589              select loop.  If n is specified, resume  at  the  nth  enclosing
4590              loop.   n  must  be  ≥  1.   If  n is greater than the number of
4591              enclosing loops, the  last  enclosing  loop  (the  ``top-level''
4592              loop) is resumed.  The return value is 0 unless n is not greater
4593              than or equal to 1.
4594
4595       declare [-aAfFgilnrtux] [-p] [name[=value] ...]
4596       typeset [-aAfFgilnrtux] [-p] [name[=value] ...]
4597              Declare variables and/or give them attributes.  If no names  are
4598              given  then display the values of variables.  The -p option will
4599              display the attributes and values of each name.  When -p is used
4600              with  name  arguments, additional options, other than -f and -F,
4601              are ignored.  When -p is supplied  without  name  arguments,  it
4602              will  display  the attributes and values of all variables having
4603              the attributes specified by the additional options.  If no other
4604              options   are   supplied  with  -p,  declare  will  display  the
4605              attributes and values of all shell  variables.   The  -f  option
4606              will  restrict  the  display  to shell functions.  The -F option
4607              inhibits the display of function definitions; only the  function
4608              name  and  attributes are printed.  If the extdebug shell option
4609              is enabled using shopt, the source file  name  and  line  number
4610              where each name is defined are displayed as well.  The -F option
4611              implies -f.  The -g option forces variables  to  be  created  or
4612              modified at the global scope, even when declare is executed in a
4613              shell function.  It is ignored in all other cases.  The  follow‐
4614              ing options can be used to restrict output to variables with the
4615              specified attribute or to give variables attributes:
4616              -a     Each name  is  an  indexed  array  variable  (see  Arrays
4617                     above).
4618              -A     Each  name  is  an associative array variable (see Arrays
4619                     above).
4620              -f     Use function names only.
4621              -i     The variable is treated as an integer; arithmetic evalua‐
4622                     tion  (see ARITHMETIC EVALUATION above) is performed when
4623                     the variable is assigned a value.
4624              -l     When the variable is assigned  a  value,  all  upper-case
4625                     characters  are  converted to lower-case.  The upper-case
4626                     attribute is disabled.
4627              -n     Give each name the nameref attribute, making  it  a  name
4628                     reference  to  another  variable.  That other variable is
4629                     defined by the value of name.   All  references,  assign‐
4630                     ments,  and attribute modifications to name, except those
4631                     using or changing the -n attribute itself, are  performed
4632                     on  the variable referenced by name's value.  The nameref
4633                     attribute cannot be applied to array variables.
4634              -r     Make names readonly.  These names cannot then be assigned
4635                     values by subsequent assignment statements or unset.
4636              -t     Give  each  name  the  trace attribute.  Traced functions
4637                     inherit the DEBUG  and  RETURN  traps  from  the  calling
4638                     shell.   The  trace  attribute has no special meaning for
4639                     variables.
4640              -u     When the variable is assigned  a  value,  all  lower-case
4641                     characters  are  converted to upper-case.  The lower-case
4642                     attribute is disabled.
4643              -x     Mark names for export  to  subsequent  commands  via  the
4644                     environment.
4645
4646              Using  `+'  instead of `-' turns off the attribute instead, with
4647              the exceptions that +a and +A may not be used to  destroy  array
4648              variables  and  +r will not remove the readonly attribute.  When
4649              used in a function, declare and typeset make each name local, as
4650              with  the local command, unless the -g option is supplied.  If a
4651              variable name is followed by =value, the value of  the  variable
4652              is  set  to value.  When using -a or -A and the compound assign‐
4653              ment syntax to create array variables, additional attributes  do
4654              not  take effect until subsequent assignments.  The return value
4655              is 0 unless an invalid option is encountered, an attempt is made
4656              to define a function using ``-f foo=bar'', an attempt is made to
4657              assign a value to a readonly variable, an  attempt  is  made  to
4658              assign  a  value to an array variable without using the compound
4659              assignment syntax (see Arrays above), one of the names is not  a
4660              valid  shell variable name, an attempt is made to turn off read‐
4661              only status for a readonly variable, an attempt is made to  turn
4662              off array status for an array variable, or an attempt is made to
4663              display a non-existent function with -f.
4664
4665       dirs [-clpv] [+n] [-n]
4666              Without options,  displays  the  list  of  currently  remembered
4667              directories.   The  default  display  is  on  a single line with
4668              directory names separated by spaces.  Directories are  added  to
4669              the  list  with  the  pushd  command;  the  popd command removes
4670              entries from the list.  The  current  directory  is  always  the
4671              first directory in the stack.
4672              -c     Clears  the  directory  stack  by  deleting  all  of  the
4673                     entries.
4674              -l     Produces a listing  using  full  pathnames;  the  default
4675                     listing format uses a tilde to denote the home directory.
4676              -p     Print the directory stack with one entry per line.
4677              -v     Print  the  directory stack with one entry per line, pre‐
4678                     fixing each entry with its index in the stack.
4679              +n     Displays the nth entry counting from the left of the list
4680                     shown by dirs when invoked without options, starting with
4681                     zero.
4682              -n     Displays the nth entry counting from  the  right  of  the
4683                     list shown by dirs when invoked without options, starting
4684                     with zero.
4685
4686              The return value is 0 unless an invalid option is supplied or  n
4687              indexes beyond the end of the directory stack.
4688
4689       disown [-ar] [-h] [jobspec ... | pid ... ]
4690              Without  options,  remove  each jobspec from the table of active
4691              jobs.  If jobspec is not present, and neither the -a nor the  -r
4692              option  is  supplied, the current job is used.  If the -h option
4693              is given, each jobspec is not removed from  the  table,  but  is
4694              marked  so  that  SIGHUP  is  not  sent  to the job if the shell
4695              receives a SIGHUP.  If no jobspec is  supplied,  the  -a  option
4696              means  to  remove or mark all jobs; the -r option without a job‐
4697              spec argument restricts operation to running jobs.   The  return
4698              value is 0 unless a jobspec does not specify a valid job.
4699
4700       echo [-neE] [arg ...]
4701              Output  the  args,  separated  by spaces, followed by a newline.
4702              The return status is 0 unless a write error occurs.   If  -n  is
4703              specified, the trailing newline is suppressed.  If the -e option
4704              is given,  interpretation  of  the  following  backslash-escaped
4705              characters  is  enabled.  The -E option disables the interpreta‐
4706              tion of these escape characters, even on systems where they  are
4707              interpreted  by  default.  The xpg_echo shell option may be used
4708              to dynamically determine  whether  or  not  echo  expands  these
4709              escape  characters  by  default.   echo does not interpret -- to
4710              mean the end of options.  echo interprets the  following  escape
4711              sequences:
4712              \a     alert (bell)
4713              \b     backspace
4714              \c     suppress further output
4715              \e
4716              \E     an escape character
4717              \f     form feed
4718              \n     new line
4719              \r     carriage return
4720              \t     horizontal tab
4721              \v     vertical tab
4722              \\     backslash
4723              \0nnn  the  eight-bit  character  whose value is the octal value
4724                     nnn (zero to three octal digits)
4725              \xHH   the eight-bit character whose value  is  the  hexadecimal
4726                     value HH (one or two hex digits)
4727              \uHHHH the  Unicode (ISO/IEC 10646) character whose value is the
4728                     hexadecimal value HHHH (one to four hex digits)
4729              \UHHHHHHHH
4730                     the Unicode (ISO/IEC 10646) character whose value is  the
4731                     hexadecimal value HHHHHHHH (one to eight hex digits)
4732
4733       enable [-a] [-dnps] [-f filename] [name ...]
4734              Enable  and disable builtin shell commands.  Disabling a builtin
4735              allows a disk command which has the same name as a shell builtin
4736              to  be  executed without specifying a full pathname, even though
4737              the shell normally searches for builtins before  disk  commands.
4738              If  -n  is  used,  each  name  is disabled; otherwise, names are
4739              enabled.  For example, to use the test binary found via the PATH
4740              instead  of  the  shell builtin version, run ``enable -n test''.
4741              The -f option means to load the new builtin  command  name  from
4742              shared object filename, on systems that support dynamic loading.
4743              The -d option will delete a builtin previously loaded  with  -f.
4744              If no name arguments are given, or if the -p option is supplied,
4745              a list of shell builtins is printed.  With no other option argu‐
4746              ments,  the  list consists of all enabled shell builtins.  If -n
4747              is supplied, only disabled builtins are printed.  If -a is  sup‐
4748              plied,  the  list printed includes all builtins, with an indica‐
4749              tion of whether or not each is enabled.  If -s is supplied,  the
4750              output  is restricted to the POSIX special builtins.  The return
4751              value is 0 unless a name is not a shell builtin or there  is  an
4752              error loading a new builtin from a shared object.
4753
4754       eval [arg ...]
4755              The  args  are read and concatenated together into a single com‐
4756              mand.  This command is then read and executed by the shell,  and
4757              its  exit status is returned as the value of eval.  If there are
4758              no args, or only null arguments, eval returns 0.
4759
4760       exec [-cl] [-a name] [command [arguments]]
4761              If command is specified, it replaces the shell.  No new  process
4762              is  created.  The arguments become the arguments to command.  If
4763              the -l option is supplied, the shell places a dash at the begin‐
4764              ning  of  the  zeroth  argument passed to command.  This is what
4765              login(1) does.  The -c option causes command to be executed with
4766              an  empty environment.  If -a is supplied, the shell passes name
4767              as the zeroth argument to the executed command.  If command can‐
4768              not  be executed for some reason, a non-interactive shell exits,
4769              unless the execfail shell option is enabled.  In that  case,  it
4770              returns  failure.   An  interactive shell returns failure if the
4771              file cannot be executed.  A subshell  exits  unconditionally  if
4772              exec  fails.  If command is not specified, any redirections take
4773              effect in the current shell, and the return  status  is  0.   If
4774              there is a redirection error, the return status is 1.
4775
4776       exit [n]
4777              Cause  the  shell  to exit with a status of n.  If n is omitted,
4778              the exit status is that of the last command executed.  A trap on
4779              EXIT is executed before the shell terminates.
4780
4781       export [-fn] [name[=word]] ...
4782       export -p
4783              The  supplied names are marked for automatic export to the envi‐
4784              ronment of subsequently executed commands.  If the -f option  is
4785              given,  the names refer to functions.  If no names are given, or
4786              if the -p option is supplied, a list of names  of  all  exported
4787              variables  is printed.  The -n option causes the export property
4788              to be removed from each name.  If a variable name is followed by
4789              =word, the value of the variable is set to word.  export returns
4790              an exit status of 0 unless an invalid option is encountered, one
4791              of  the  names is not a valid shell variable name, or -f is sup‐
4792              plied with a name that is not a function.
4793
4794       fc [-e ename] [-lnr] [first] [last]
4795       fc -s [pat=rep] [cmd]
4796              The first form selects a range of commands from  first  to  last
4797              from  the  history  list  and  displays or edits and re-executes
4798              them.  First and last may be specified as a  string  (to  locate
4799              the  last command beginning with that string) or as a number (an
4800              index into the history list, where a negative number is used  as
4801              an  offset  from  the  current  command number).  If last is not
4802              specified, it is set to the current command for listing (so that
4803              ``fc  -l  -10'' prints the last 10 commands) and to first other‐
4804              wise.  If first is not specified, it is set to the previous com‐
4805              mand for editing and -16 for listing.
4806
4807              The  -n option suppresses the command numbers when listing.  The
4808              -r option reverses the order of the commands.  If the -l  option
4809              is  given,  the  commands are listed on standard output.  Other‐
4810              wise, the editor given by ename is invoked on a file  containing
4811              those  commands.  If ename is not given, the value of the FCEDIT
4812              variable is used, and the value of EDITOR if FCEDIT is not  set.
4813              If  neither  variable  is set, vi is used.  When editing is com‐
4814              plete, the edited commands are echoed and executed.
4815
4816              In the second form, command is re-executed after  each  instance
4817              of  pat  is replaced by rep.  Command is interpreted the same as
4818              first above.  A useful alias to use with this is ``r="fc  -s"'',
4819              so  that  typing  ``r  cc'' runs the last command beginning with
4820              ``cc'' and typing ``r'' re-executes the last command.
4821
4822              If the first form is used, the  return  value  is  0  unless  an
4823              invalid  option  is encountered or first or last specify history
4824              lines out of range.  If the -e option is  supplied,  the  return
4825              value is the value of the last command executed or failure if an
4826              error occurs with the temporary file of commands.  If the second
4827              form  is  used, the return status is that of the command re-exe‐
4828              cuted, unless cmd does not specify  a  valid  history  line,  in
4829              which case fc returns failure.
4830
4831       fg [jobspec]
4832              Resume  jobspec  in the foreground, and make it the current job.
4833              If jobspec is not present, the shell's notion of the current job
4834              is  used.   The  return value is that of the command placed into
4835              the foreground, or failure if run when job control  is  disabled
4836              or, when run with job control enabled, if jobspec does not spec‐
4837              ify a valid job or jobspec specifies  a  job  that  was  started
4838              without job control.
4839
4840       getopts optstring name [args]
4841              getopts  is used by shell procedures to parse positional parame‐
4842              ters.  optstring contains the option  characters  to  be  recog‐
4843              nized;  if  a  character  is  followed by a colon, the option is
4844              expected to have an argument, which should be separated from  it
4845              by  white space.  The colon and question mark characters may not
4846              be used as option characters.  Each time it is invoked,  getopts
4847              places  the next option in the shell variable name, initializing
4848              name if it does not exist, and the index of the next argument to
4849              be processed into the variable OPTIND.  OPTIND is initialized to
4850              1 each time the shell or a shell script  is  invoked.   When  an
4851              option  requires  an argument, getopts places that argument into
4852              the variable OPTARG.  The shell does not reset OPTIND  automati‐
4853              cally;  it  must  be  manually  reset  between multiple calls to
4854              getopts within the same shell invocation if a new set of parame‐
4855              ters is to be used.
4856
4857              When  the  end  of  options is encountered, getopts exits with a
4858              return value greater than zero.  OPTIND is set to the  index  of
4859              the first non-option argument, and name is set to ?.
4860
4861              getopts  normally  parses the positional parameters, but if more
4862              arguments are given in args, getopts parses those instead.
4863
4864              getopts can report errors in two ways.  If the  first  character
4865              of  optstring  is  a  colon, silent error reporting is used.  In
4866              normal operation, diagnostic messages are printed  when  invalid
4867              options  or  missing  option  arguments are encountered.  If the
4868              variable OPTERR is set to 0, no  error  messages  will  be  dis‐
4869              played, even if the first character of optstring is not a colon.
4870
4871              If an invalid option is seen, getopts places ? into name and, if
4872              not silent, prints an  error  message  and  unsets  OPTARG.   If
4873              getopts  is  silent,  the  option  character  found is placed in
4874              OPTARG and no diagnostic message is printed.
4875
4876              If a required argument is not found, and getopts is not  silent,
4877              a  question  mark  (?) is placed in name, OPTARG is unset, and a
4878              diagnostic message is printed.  If getopts  is  silent,  then  a
4879              colon  (:)  is  placed  in  name and OPTARG is set to the option
4880              character found.
4881
4882              getopts returns true if an option, specified or unspecified,  is
4883              found.  It returns false if the end of options is encountered or
4884              an error occurs.
4885
4886       hash [-lr] [-p filename] [-dt] [name]
4887              Each time hash is invoked, the full pathname of the command name
4888              is  determined  by searching the directories in $PATH and remem‐
4889              bered.  Any previously-remembered pathname is discarded.  If the
4890              -p option is supplied, no path search is performed, and filename
4891              is used as the full filename of  the  command.   The  -r  option
4892              causes  the  shell  to  forget all remembered locations.  The -d
4893              option causes the shell to forget  the  remembered  location  of
4894              each  name.   If the -t option is supplied, the full pathname to
4895              which each name corresponds is printed.  If multiple name  argu‐
4896              ments  are  supplied  with  -t,  the  name is printed before the
4897              hashed full pathname.  The -l option causes output  to  be  dis‐
4898              played in a format that may be reused as input.  If no arguments
4899              are given, or if only -l is supplied, information  about  remem‐
4900              bered  commands  is printed.  The return status is true unless a
4901              name is not found or an invalid option is supplied.
4902
4903       help [-dms] [pattern]
4904              Display helpful information about builtin commands.  If  pattern
4905              is  specified, help gives detailed help on all commands matching
4906              pattern; otherwise help for all the builtins and  shell  control
4907              structures is printed.
4908              -d     Display a short description of each pattern
4909              -m     Display the description of each pattern in a manpage-like
4910                     format
4911              -s     Display only a short usage synopsis for each pattern
4912
4913              The return status is 0 unless no command matches pattern.
4914
4915       history [n]
4916       history -c
4917       history -d offset
4918       history -d start-end
4919       history -anrw [filename]
4920       history -p arg [arg ...]
4921       history -s arg [arg ...]
4922              With no options, display the command history list with line num‐
4923              bers.  Lines listed with a * have been modified.  An argument of
4924              n lists only the last n lines.  If the shell variable  HISTTIME‐
4925              FORMAT  is  set  and not null, it is used as a format string for
4926              strftime(3) to display the time stamp associated with each  dis‐
4927              played  history  entry.  No intervening blank is printed between
4928              the formatted time stamp and the history line.  If  filename  is
4929              supplied,  it  is  used as the name of the history file; if not,
4930              the value of HISTFILE is used.  Options, if supplied,  have  the
4931              following meanings:
4932              -c     Clear the history list by deleting all the entries.
4933              -d offset
4934                     Delete  the  history entry at position offset.  If offset
4935                     is negative, it is interpreted as relative to one greater
4936                     than the last history position, so negative indices count
4937                     back from the end of the history,  and  an  index  of  -1
4938                     refers to the current history -d command.
4939              -d start-end
4940                     Delete  the  history  entries between positions start and
4941                     end, inclusive.  Positive and negative values  for  start
4942                     and end are interpreted as described above.
4943              -a     Append  the  ``new''  history  lines to the history file.
4944                     These are history lines entered since  the  beginning  of
4945                     the current bash session, but not already appended to the
4946                     history file.
4947              -n     Read the history lines not already read from the  history
4948                     file  into  the  current  history  list.  These are lines
4949                     appended to the history file since the beginning  of  the
4950                     current bash session.
4951              -r     Read  the contents of the history file and append them to
4952                     the current history list.
4953              -w     Write the current history list to the history file, over‐
4954                     writing the history file's contents.
4955              -p     Perform  history  substitution  on the following args and
4956                     display the result on  the  standard  output.   Does  not
4957                     store  the results in the history list.  Each arg must be
4958                     quoted to disable normal history expansion.
4959              -s     Store the args in the history list  as  a  single  entry.
4960                     The  last  command  in the history list is removed before
4961                     the args are added.
4962
4963              If the HISTTIMEFORMAT variable is set, the time  stamp  informa‐
4964              tion  associated  with each history entry is written to the his‐
4965              tory file, marked with the history comment character.  When  the
4966              history  file  is read, lines beginning with the history comment
4967              character followed immediately by a  digit  are  interpreted  as
4968              timestamps for the following history entry.  The return value is
4969              0 unless an invalid option is encountered, an error occurs while
4970              reading  or  writing the history file, an invalid offset is sup‐
4971              plied as an argument to -d, or the history expansion supplied as
4972              an argument to -p fails.
4973
4974       jobs [-lnprs] [ jobspec ... ]
4975       jobs -x command [ args ... ]
4976              The first form lists the active jobs.  The options have the fol‐
4977              lowing meanings:
4978              -l     List process IDs in addition to the normal information.
4979              -n     Display information only about  jobs  that  have  changed
4980                     status since the user was last notified of their status.
4981              -p     List  only  the  process  ID  of  the job's process group
4982                     leader.
4983              -r     Display only running jobs.
4984              -s     Display only stopped jobs.
4985
4986              If jobspec is given, output is restricted to  information  about
4987              that  job.   The  return status is 0 unless an invalid option is
4988              encountered or an invalid jobspec is supplied.
4989
4990              If the -x option is supplied, jobs replaces any jobspec found in
4991              command  or  args  with  the corresponding process group ID, and
4992              executes command passing it args, returning its exit status.
4993
4994       kill [-s sigspec | -n signum | -sigspec] [pid | jobspec] ...
4995       kill -l|-L [sigspec | exit_status]
4996              Send the signal named by sigspec  or  signum  to  the  processes
4997              named  by  pid or jobspec.  sigspec is either a case-insensitive
4998              signal name such as SIGKILL (with or without the SIG prefix)  or
4999              a  signal  number; signum is a signal number.  If sigspec is not
5000              present, then SIGTERM is assumed.  An argument of -l  lists  the
5001              signal  names.   If any arguments are supplied when -l is given,
5002              the names of the signals  corresponding  to  the  arguments  are
5003              listed, and the return status is 0.  The exit_status argument to
5004              -l is a number specifying either a signal  number  or  the  exit
5005              status  of  a  process terminated by a signal.  The -L option is
5006              equivalent to -l.  kill returns true if at least one signal  was
5007              successfully  sent,  or  false  if an error occurs or an invalid
5008              option is encountered.
5009
5010       let arg [arg ...]
5011              Each arg is an arithmetic expression to be evaluated (see ARITH‐
5012              METIC  EVALUATION  above).   If the last arg evaluates to 0, let
5013              returns 1; 0 is returned otherwise.
5014
5015       local [option] [name[=value] ... | - ]
5016              For each argument, a local variable named name is  created,  and
5017              assigned  value.   The option can be any of the options accepted
5018              by declare.  When local is used within a function, it causes the
5019              variable  name  to have a visible scope restricted to that func‐
5020              tion and its children.  If name is -, the set of  shell  options
5021              is  made  local to the function in which local is invoked: shell
5022              options changed using the set builtin inside  the  function  are
5023              restored  to  their  original  values when the function returns.
5024              With no operands, local writes a list of local variables to  the
5025              standard  output.  It is an error to use local when not within a
5026              function.  The return status is 0 unless local is used outside a
5027              function,  an  invalid  name  is supplied, or name is a readonly
5028              variable.
5029
5030       logout Exit a login shell.
5031
5032       mapfile [-d delim] [-n count] [-O origin] [-s count] [-t] [-u  fd]  [-C
5033       callback] [-c quantum] [array]
5034       readarray [-d delim] [-n count] [-O origin] [-s count] [-t] [-u fd] [-C
5035       callback] [-c quantum] [array]
5036              Read lines from the standard input into the indexed array  vari‐
5037              able  array, or from file descriptor fd if the -u option is sup‐
5038              plied.  The variable MAPFILE is the default array.  Options,  if
5039              supplied, have the following meanings:
5040              -d     The  first  character  of delim is used to terminate each
5041                     input line, rather than newline.  If delim is  the  empty
5042                     string, mapfile will terminate a line when it reads a NUL
5043                     character.
5044              -n     Copy at most count lines.  If count is 0, all  lines  are
5045                     copied.
5046              -O     Begin  assigning  to  array at index origin.  The default
5047                     index is 0.
5048              -s     Discard the first count lines read.
5049              -t     Remove a trailing delim (default newline) from each  line
5050                     read.
5051              -u     Read  lines  from file descriptor fd instead of the stan‐
5052                     dard input.
5053              -C     Evaluate callback each time quantum lines are read.   The
5054                     -c option specifies quantum.
5055              -c     Specify  the  number  of  lines read between each call to
5056                     callback.
5057
5058              If -C is specified without -c,  the  default  quantum  is  5000.
5059              When callback is evaluated, it is supplied the index of the next
5060              array element to be assigned and the line to be assigned to that
5061              element  as  additional  arguments.  callback is evaluated after
5062              the line is read but before the array element is assigned.
5063
5064              If not supplied with an  explicit  origin,  mapfile  will  clear
5065              array before assigning to it.
5066
5067              mapfile  returns successfully unless an invalid option or option
5068              argument is supplied, array is invalid or  unassignable,  or  if
5069              array is not an indexed array.
5070
5071       popd [-n] [+n] [-n]
5072              Removes  entries  from  the directory stack.  With no arguments,
5073              removes the top directory from the stack, and performs a  cd  to
5074              the new top directory.  Arguments, if supplied, have the follow‐
5075              ing meanings:
5076              -n     Suppresses the normal change of directory  when  removing
5077                     directories  from  the  stack,  so that only the stack is
5078                     manipulated.
5079              +n     Removes the nth entry counting from the left of the  list
5080                     shown  by  dirs, starting with zero.  For example: ``popd
5081                     +0'' removes the first directory, ``popd +1'' the second.
5082              -n     Removes the nth entry counting from the right of the list
5083                     shown  by  dirs, starting with zero.  For example: ``popd
5084                     -0'' removes the last directory, ``popd -1'' the next  to
5085                     last.
5086
5087              If  the popd command is successful, a dirs is performed as well,
5088              and the return status is 0.  popd returns false  if  an  invalid
5089              option is encountered, the directory stack is empty, a non-exis‐
5090              tent directory stack entry is specified, or the directory change
5091              fails.
5092
5093       printf [-v var] format [arguments]
5094              Write  the  formatted arguments to the standard output under the
5095              control of the format.  The -v option causes the  output  to  be
5096              assigned  to  the  variable var rather than being printed to the
5097              standard output.
5098
5099              The format is a character string which contains three  types  of
5100              objects:  plain  characters, which are simply copied to standard
5101              output, character escape  sequences,  which  are  converted  and
5102              copied  to  the standard output, and format specifications, each
5103              of which causes printing of the next  successive  argument.   In
5104              addition to the standard printf(1) format specifications, printf
5105              interprets the following extensions:
5106              %b     causes printf to expand backslash escape sequences in the
5107                     corresponding argument in the same way as echo -e.
5108              %q     causes  printf  to output the corresponding argument in a
5109                     format that can be reused as shell input.
5110              %(datefmt)T
5111                     causes printf to output the  date-time  string  resulting
5112                     from  using  datefmt  as a format string for strftime(3).
5113                     The corresponding argument is an integer representing the
5114                     number  of seconds since the epoch.  Two special argument
5115                     values may be used: -1 represents the current  time,  and
5116                     -2  represents  the  time  the  shell was invoked.  If no
5117                     argument is specified, conversion behaves as  if  -1  had
5118                     been  given.   This  is  an exception to the usual printf
5119                     behavior.
5120
5121              Arguments to non-string format specifiers are treated as C  con‐
5122              stants, except that a leading plus or minus sign is allowed, and
5123              if the leading character is a single or double quote, the  value
5124              is the ASCII value of the following character.
5125
5126              The  format  is  reused as necessary to consume all of the argu‐
5127              ments.  If the format requires more arguments than are supplied,
5128              the  extra  format  specifications  behave as if a zero value or
5129              null string, as appropriate,  had  been  supplied.   The  return
5130              value is zero on success, non-zero on failure.
5131
5132       pushd [-n] [+n] [-n]
5133       pushd [-n] [dir]
5134              Adds  a  directory to the top of the directory stack, or rotates
5135              the stack, making the new top of the stack the  current  working
5136              directory.   With  no  arguments,  pushd  exchanges  the top two
5137              directories and returns 0, unless the directory stack is  empty.
5138              Arguments, if supplied, have the following meanings:
5139              -n     Suppresses  the  normal change of directory when rotating
5140                     or adding directories to the  stack,  so  that  only  the
5141                     stack is manipulated.
5142              +n     Rotates  the  stack  so  that the nth directory (counting
5143                     from the left of the list shown by  dirs,  starting  with
5144                     zero) is at the top.
5145              -n     Rotates  the  stack  so  that the nth directory (counting
5146                     from the right of the list shown by dirs,  starting  with
5147                     zero) is at the top.
5148              dir    Adds dir to the directory stack at the top, making it the
5149                     new current working directory as if it had been  supplied
5150                     as the argument to the cd builtin.
5151
5152              If the pushd command is successful, a dirs is performed as well.
5153              If the first form is used, pushd returns 0 unless the cd to  dir
5154              fails.   With the second form, pushd returns 0 unless the direc‐
5155              tory stack is empty, a non-existent directory stack  element  is
5156              specified,  or the directory change to the specified new current
5157              directory fails.
5158
5159       pwd [-LP]
5160              Print the absolute pathname of the  current  working  directory.
5161              The pathname printed contains no symbolic links if the -P option
5162              is supplied or the -o physical option to the set builtin command
5163              is  enabled.  If the -L option is used, the pathname printed may
5164              contain symbolic links.  The return status is 0 unless an  error
5165              occurs  while  reading  the  name of the current directory or an
5166              invalid option is supplied.
5167
5168       read [-ers] [-a aname] [-d delim] [-i text] [-n nchars] [-N nchars] [-p
5169       prompt] [-t timeout] [-u fd] [name ...]
5170              One  line  is  read  from  the  standard input, or from the file
5171              descriptor fd supplied as an argument to the  -u  option,  split
5172              into  words  as  described  above  under Word Splitting, and the
5173              first word is assigned to the first name, the second word to the
5174              second name, and so on.  If there are more words than names, the
5175              remaining words and their intervening delimiters are assigned to
5176              the  last  name.   If  there are fewer words read from the input
5177              stream than names, the remaining names are assigned  empty  val‐
5178              ues.   The  characters  in  IFS  are used to split the line into
5179              words  using  the  same  rules  the  shell  uses  for  expansion
5180              (described above under Word Splitting).  The backslash character
5181              (\) may be used to remove any special meaning for the next char‐
5182              acter  read  and  for  line continuation.  Options, if supplied,
5183              have the following meanings:
5184              -a aname
5185                     The words are assigned to sequential indices of the array
5186                     variable aname, starting at 0.  aname is unset before any
5187                     new  values  are  assigned.   Other  name  arguments  are
5188                     ignored.
5189              -d delim
5190                     The  first  character  of  delim is used to terminate the
5191                     input line, rather than newline.  If delim is  the  empty
5192                     string,  read  will  terminate a line when it reads a NUL
5193                     character.
5194              -e     If the standard input is coming from a terminal, readline
5195                     (see  READLINE  above) is used to obtain the line.  Read‐
5196                     line uses the current (or default, if  line  editing  was
5197                     not  previously  active) editing settings, but uses Read‐
5198                     line's default filename completion.
5199              -i text
5200                     If readline is being used  to  read  the  line,  text  is
5201                     placed into the editing buffer before editing begins.
5202              -n nchars
5203                     read  returns after reading nchars characters rather than
5204                     waiting for a complete line of input, but honors a delim‐
5205                     iter  if fewer than nchars characters are read before the
5206                     delimiter.
5207              -N nchars
5208                     read returns  after  reading  exactly  nchars  characters
5209                     rather  than waiting for a complete line of input, unless
5210                     EOF is encountered or read times out.  Delimiter  charac‐
5211                     ters  encountered  in the input are not treated specially
5212                     and do not cause read to return until  nchars  characters
5213                     are  read.   The result is not split on the characters in
5214                     IFS; the intent is that the variable is assigned  exactly
5215                     the characters read (with the exception of backslash; see
5216                     the -r option below).
5217              -p prompt
5218                     Display prompt on standard error, without a trailing new‐
5219                     line, before attempting to read any input.  The prompt is
5220                     displayed only if input is coming from a terminal.
5221              -r     Backslash does not act as an escape character.  The back‐
5222                     slash  is considered to be part of the line.  In particu‐
5223                     lar, a backslash-newline pair may not then be used  as  a
5224                     line continuation.
5225              -s     Silent mode.  If input is coming from a terminal, charac‐
5226                     ters are not echoed.
5227              -t timeout
5228                     Cause read to time out and return failure if  a  complete
5229                     line  of  input  (or a specified number of characters) is
5230                     not read within timeout seconds.  timeout may be a  deci‐
5231                     mal  number with a fractional portion following the deci‐
5232                     mal point.  This option is  only  effective  if  read  is
5233                     reading  input  from  a  terminal, pipe, or other special
5234                     file; it has no effect when reading from  regular  files.
5235                     If read times out, read saves any partial input read into
5236                     the specified variable  name.   If  timeout  is  0,  read
5237                     returns  immediately,  without  trying  to read any data.
5238                     The exit status is 0 if input is available on the  speci‐
5239                     fied  file descriptor, non-zero otherwise.  The exit sta‐
5240                     tus is greater than 128 if the timeout is exceeded.
5241              -u fd  Read input from file descriptor fd.
5242
5243              If no names are supplied, the line read is assigned to the vari‐
5244              able  REPLY.   The  exit  status  is zero, unless end-of-file is
5245              encountered, read times out (in which case the status is greater
5246              than  128),  a variable assignment error (such as assigning to a
5247              readonly variable) occurs, or an invalid file descriptor is sup‐
5248              plied as the argument to -u.
5249
5250       readonly [-aAf] [-p] [name[=word] ...]
5251              The  given  names are marked readonly; the values of these names
5252              may not be changed by subsequent assignment.  If the  -f  option
5253              is  supplied,  the  functions  corresponding to the names are so
5254              marked.  The  -a  option  restricts  the  variables  to  indexed
5255              arrays;  the  -A  option  restricts the variables to associative
5256              arrays.  If both options are supplied, -A takes precedence.   If
5257              no  name arguments are given, or if the -p option is supplied, a
5258              list of all readonly names is printed.  The other options may be
5259              used  to  restrict the output to a subset of the set of readonly
5260              names.  The -p option causes output to be displayed in a  format
5261              that  may be reused as input.  If a variable name is followed by
5262              =word, the value of the variable is set  to  word.   The  return
5263              status  is 0 unless an invalid option is encountered, one of the
5264              names is not a valid shell variable name, or -f is supplied with
5265              a name that is not a function.
5266
5267       return [n]
5268              Causes  a function to stop executing and return the value speci‐
5269              fied by n to its caller.  If n is omitted, the return status  is
5270              that  of  the  last  command  executed in the function body.  If
5271              return is executed by a trap handler, the last command  used  to
5272              determine  the  status  is  the last command executed before the
5273              trap handler.  If return is executed during a  DEBUG  trap,  the
5274              last  command  used  to determine the status is the last command
5275              executed by the trap handler  before  return  was  invoked.   If
5276              return  is  used  outside  a function, but during execution of a
5277              script by the .  (source) command, it causes the shell  to  stop
5278              executing  that script and return either n or the exit status of
5279              the last command executed within the script as the  exit  status
5280              of  the script.  If n is supplied, the return value is its least
5281              significant 8 bits.  The return status is non-zero if return  is
5282              supplied  a  non-numeric argument, or is used outside a function
5283              and not during execution of a script by . or source.   Any  com‐
5284              mand  associated  with the RETURN trap is executed before execu‐
5285              tion resumes after the function or script.
5286
5287       set [--abefhkmnptuvxBCEHPT] [-o option-name] [arg ...]
5288       set [+abefhkmnptuvxBCEHPT] [+o option-name] [arg ...]
5289              Without options, the name and value of each shell  variable  are
5290              displayed in a format that can be reused as input for setting or
5291              resetting the currently-set variables.  Read-only variables can‐
5292              not  be  reset.  In posix mode, only shell variables are listed.
5293              The output is sorted according  to  the  current  locale.   When
5294              options  are specified, they set or unset shell attributes.  Any
5295              arguments remaining after option processing are treated as  val‐
5296              ues for the positional parameters and are assigned, in order, to
5297              $1, $2, ...  $n.  Options,  if  specified,  have  the  following
5298              meanings:
5299              -a      Each variable or function that is created or modified is
5300                      given the export attribute and marked for export to  the
5301                      environment of subsequent commands.
5302              -b      Report  the status of terminated background jobs immedi‐
5303                      ately, rather than before the next primary prompt.  This
5304                      is effective only when job control is enabled.
5305              -e      Exit  immediately  if a pipeline (which may consist of a
5306                      single simple command), a list, or  a  compound  command
5307                      (see SHELL GRAMMAR above), exits with a non-zero status.
5308                      The shell does not exit if the  command  that  fails  is
5309                      part  of  the command list immediately following a while
5310                      or until keyword, part of the test following the  if  or
5311                      elif  reserved  words, part of any command executed in a
5312                      && or || list except the command following the final  &&
5313                      or ||, any command in a pipeline but the last, or if the
5314                      command's return value is being inverted with !.   If  a
5315                      compound  command  other  than a subshell returns a non-
5316                      zero status because a command failed while -e was  being
5317                      ignored,  the  shell  does  not exit.  A trap on ERR, if
5318                      set, is executed before the shell  exits.   This  option
5319                      applies to the shell environment and each subshell envi‐
5320                      ronment separately (see  COMMAND  EXECUTION  ENVIRONMENT
5321                      above), and may cause subshells to exit before executing
5322                      all the commands in the subshell.
5323
5324                      If a compound command or shell function  executes  in  a
5325                      context  where -e is being ignored, none of the commands
5326                      executed within the compound command  or  function  body
5327                      will  be  affected  by the -e setting, even if -e is set
5328                      and a command returns a failure status.  If  a  compound
5329                      command  or  shell function sets -e while executing in a
5330                      context where -e is ignored, that setting will not  have
5331                      any  effect  until  the  compound command or the command
5332                      containing the function call completes.
5333              -f      Disable pathname expansion.
5334              -h      Remember the location of commands as they are looked  up
5335                      for execution.  This is enabled by default.
5336              -k      All  arguments  in the form of assignment statements are
5337                      placed in the environment for a command, not just  those
5338                      that precede the command name.
5339              -m      Monitor  mode.   Job control is enabled.  This option is
5340                      on by default for interactive  shells  on  systems  that
5341                      support  it  (see JOB CONTROL above).  All processes run
5342                      in a separate process group.  When a background job com‐
5343                      pletes, the shell prints a line containing its exit sta‐
5344                      tus.
5345              -n      Read commands but do not execute them.  This may be used
5346                      to  check  a  shell  script  for syntax errors.  This is
5347                      ignored by interactive shells.
5348              -o option-name
5349                      The option-name can be one of the following:
5350                      allexport
5351                              Same as -a.
5352                      braceexpand
5353                              Same as -B.
5354                      emacs   Use an emacs-style command line  editing  inter‐
5355                              face.  This is enabled by default when the shell
5356                              is interactive, unless the shell is started with
5357                              the  --noediting  option.  This also affects the
5358                              editing interface used for read -e.
5359                      errexit Same as -e.
5360                      errtrace
5361                              Same as -E.
5362                      functrace
5363                              Same as -T.
5364                      hashall Same as -h.
5365                      histexpand
5366                              Same as -H.
5367                      history Enable command history, as described above under
5368                              HISTORY.  This option is on by default in inter‐
5369                              active shells.
5370                      ignoreeof
5371                              The  effect  is  as   if   the   shell   command
5372                              ``IGNOREEOF=10''  had  been  executed (see Shell
5373                              Variables above).
5374                      keyword Same as -k.
5375                      monitor Same as -m.
5376                      noclobber
5377                              Same as -C.
5378                      noexec  Same as -n.
5379                      noglob  Same as -f.
5380                      nolog   Currently ignored.
5381                      notify  Same as -b.
5382                      nounset Same as -u.
5383                      onecmd  Same as -t.
5384                      physical
5385                              Same as -P.
5386                      pipefail
5387                              If set, the return value of a  pipeline  is  the
5388                              value  of  the  last (rightmost) command to exit
5389                              with a non-zero status, or zero if all  commands
5390                              in  the pipeline exit successfully.  This option
5391                              is disabled by default.
5392                      posix   Change the behavior of bash  where  the  default
5393                              operation  differs  from  the  POSIX standard to
5394                              match the standard (posix mode).  See  SEE  ALSO
5395                              below for a reference to a document that details
5396                              how posix mode affects bash's behavior.
5397                      privileged
5398                              Same as -p.
5399                      verbose Same as -v.
5400                      vi      Use a vi-style command line  editing  interface.
5401                              This also affects the editing interface used for
5402                              read -e.
5403                      xtrace  Same as -x.
5404                      If -o is supplied with no option-name, the values of the
5405                      current  options are printed.  If +o is supplied with no
5406                      option-name, a series of set commands  to  recreate  the
5407                      current  option  settings  is  displayed on the standard
5408                      output.
5409              -p      Turn on privileged mode.  In this  mode,  the  $ENV  and
5410                      $BASH_ENV  files  are not processed, shell functions are
5411                      not inherited from the environment, and  the  SHELLOPTS,
5412                      BASHOPTS,  CDPATH,  and  GLOBIGNORE  variables,  if they
5413                      appear in the environment, are ignored.  If the shell is
5414                      started  with the effective user (group) id not equal to
5415                      the real user (group) id, and the -p option is not  sup‐
5416                      plied, these actions are taken and the effective user id
5417                      is set to the real user id.  If the -p  option  is  sup‐
5418                      plied  at  startup,  the effective user id is not reset.
5419                      Turning this option off causes the  effective  user  and
5420                      group ids to be set to the real user and group ids.
5421              -t      Exit after reading and executing one command.
5422              -u      Treat unset variables and parameters other than the spe‐
5423                      cial parameters "@" and "*" as an error when  performing
5424                      parameter  expansion.   If  expansion is attempted on an
5425                      unset variable or parameter, the shell prints  an  error
5426                      message,  and, if not interactive, exits with a non-zero
5427                      status.
5428              -v      Print shell input lines as they are read.
5429              -x      After expanding each simple command, for  command,  case
5430                      command, select command, or arithmetic for command, dis‐
5431                      play the expanded value of PS4, followed by the  command
5432                      and its expanded arguments or associated word list.
5433              -B      The  shell performs brace expansion (see Brace Expansion
5434                      above).  This is on by default.
5435              -C      If set, bash does not overwrite an  existing  file  with
5436                      the  >,  >&,  and <> redirection operators.  This may be
5437                      overridden when creating output files by using the redi‐
5438                      rection operator >| instead of >.
5439              -E      If set, any trap on ERR is inherited by shell functions,
5440                      command substitutions, and commands executed in  a  sub‐
5441                      shell  environment.  The ERR trap is normally not inher‐
5442                      ited in such cases.
5443              -H      Enable !  style history substitution.  This option is on
5444                      by default when the shell is interactive.
5445              -P      If  set,  the shell does not resolve symbolic links when
5446                      executing commands such as cd that  change  the  current
5447                      working  directory.   It  uses  the  physical  directory
5448                      structure instead.  By default, bash follows the logical
5449                      chain  of  directories  when  performing  commands which
5450                      change the current directory.
5451              -T      If set, any traps on DEBUG and RETURN are  inherited  by
5452                      shell  functions,  command  substitutions,  and commands
5453                      executed in  a  subshell  environment.   The  DEBUG  and
5454                      RETURN traps are normally not inherited in such cases.
5455              --      If  no arguments follow this option, then the positional
5456                      parameters are unset.  Otherwise, the positional parame‐
5457                      ters  are  set  to  the args, even if some of them begin
5458                      with a -.
5459              -       Signal the end of options, cause all remaining  args  to
5460                      be assigned to the positional parameters.  The -x and -v
5461                      options are turned off.  If there are no args, the posi‐
5462                      tional parameters remain unchanged.
5463
5464              The  options are off by default unless otherwise noted.  Using +
5465              rather than - causes  these  options  to  be  turned  off.   The
5466              options  can  also be specified as arguments to an invocation of
5467              the shell.  The current set of options may be found in $-.   The
5468              return status is always true unless an invalid option is encoun‐
5469              tered.
5470
5471       shift [n]
5472              The positional parameters from n+1 ... are renamed  to  $1  ....
5473              Parameters  represented  by  the  numbers  $# down to $#-n+1 are
5474              unset.  n must be a non-negative number less than  or  equal  to
5475              $#.   If  n is 0, no parameters are changed.  If n is not given,
5476              it is assumed to be 1.  If n is greater than $#, the  positional
5477              parameters  are  not changed.  The return status is greater than
5478              zero if n is greater than $# or less than zero; otherwise 0.
5479
5480       shopt [-pqsu] [-o] [optname ...]
5481              Toggle the values of settings controlling optional shell  behav‐
5482              ior.   The settings can be either those listed below, or, if the
5483              -o option is used, those available with the -o option to the set
5484              builtin command.  With no options, or with the -p option, a list
5485              of all settable options is  displayed,  with  an  indication  of
5486              whether or not each is set; if optnames are supplied, the output
5487              is restricted to those options.  The -p option causes output  to
5488              be  displayed  in  a  form  that  may be reused as input.  Other
5489              options have the following meanings:
5490              -s     Enable (set) each optname.
5491              -u     Disable (unset) each optname.
5492              -q     Suppresses normal output (quiet mode); the return  status
5493                     indicates whether the optname is set or unset.  If multi‐
5494                     ple optname arguments are given with -q, the return  sta‐
5495                     tus  is zero if all optnames are enabled; non-zero other‐
5496                     wise.
5497              -o     Restricts the values of optname to be those  defined  for
5498                     the -o option to the set builtin.
5499
5500              If  either  -s  or  -u  is used with no optname arguments, shopt
5501              shows only those options which are set or  unset,  respectively.
5502              Unless  otherwise  noted, the shopt options are disabled (unset)
5503              by default.
5504
5505              The return status when listing options is zero if  all  optnames
5506              are  enabled,  non-zero  otherwise.   When  setting or unsetting
5507              options, the return status is zero unless an optname  is  not  a
5508              valid shell option.
5509
5510              The list of shopt options is:
5511
5512              assoc_expand_once
5513                      If  set,  the  shell  suppresses  multiple evaluation of
5514                      associative array subscripts during  arithmetic  expres‐
5515                      sion  evaluation, while executing builtins that can per‐
5516                      form variable assignments, and while executing  builtins
5517                      that perform array dereferencing.
5518              autocd  If  set,  a command name that is the name of a directory
5519                      is executed as if it were the argument to  the  cd  com‐
5520                      mand.  This option is only used by interactive shells.
5521              cdable_vars
5522                      If  set,  an  argument to the cd builtin command that is
5523                      not a directory is assumed to be the name of a  variable
5524                      whose value is the directory to change to.
5525              cdspell If set, minor errors in the spelling of a directory com‐
5526                      ponent in a cd command will be  corrected.   The  errors
5527                      checked for are transposed characters, a missing charac‐
5528                      ter, and one character too many.   If  a  correction  is
5529                      found,  the  corrected filename is printed, and the com‐
5530                      mand proceeds.  This option is only used by  interactive
5531                      shells.
5532              checkhash
5533                      If set, bash checks that a command found in the hash ta‐
5534                      ble exists before trying to execute  it.   If  a  hashed
5535                      command  no  longer exists, a normal path search is per‐
5536                      formed.
5537              checkjobs
5538                      If set, bash lists the status of any stopped and running
5539                      jobs  before  exiting an interactive shell.  If any jobs
5540                      are running, this causes the exit to be deferred until a
5541                      second  exit is attempted without an intervening command
5542                      (see JOB CONTROL above).   The  shell  always  postpones
5543                      exiting if any jobs are stopped.
5544              checkwinsize
5545                      If  set, bash checks the window size after each external
5546                      (non-builtin) command and,  if  necessary,  updates  the
5547                      values  of LINES and COLUMNS.  This option is enabled by
5548                      default.
5549              cmdhist If set, bash attempts to save all lines of  a  multiple-
5550                      line  command  in  the  same history entry.  This allows
5551                      easy re-editing of multi-line commands.  This option  is
5552                      enabled  by  default,  but only has an effect if command
5553                      history is enabled, as described above under HISTORY.
5554              compat31
5555                      If set, bash changes its behavior to that of version 3.1
5556                      with  respect  to quoted arguments to the [[ conditional
5557                      command's =~ operator and locale-specific string compar‐
5558                      ison  when  using  the  [[ conditional command's < and >
5559                      operators.  Bash versions prior to  bash-4.1  use  ASCII
5560                      collation and strcmp(3); bash-4.1 and later use the cur‐
5561                      rent locale's collation sequence and strcoll(3).
5562              compat32
5563                      If set, bash changes its behavior to that of version 3.2
5564                      with  respect  to locale-specific string comparison when
5565                      using the [[ conditional command's  <  and  >  operators
5566                      (see  previous  item)  and  the effect of interrupting a
5567                      command list.  Bash versions 3.2  and  earlier  continue
5568                      with  the  next command in the list after one terminates
5569                      due to an interrupt.
5570              compat40
5571                      If set, bash changes its behavior to that of version 4.0
5572                      with  respect  to locale-specific string comparison when
5573                      using the [[ conditional command's  <  and  >  operators
5574                      (see  description  of compat31) and the effect of inter‐
5575                      rupting a command list.  Bash  versions  4.0  and  later
5576                      interrupt  the  list as if the shell received the inter‐
5577                      rupt; previous versions continue with the  next  command
5578                      in the list.
5579              compat41
5580                      If  set, bash, when in posix mode, treats a single quote
5581                      in a double-quoted  parameter  expansion  as  a  special
5582                      character.   The  single quotes must match (an even num‐
5583                      ber) and the characters between the  single  quotes  are
5584                      considered  quoted.   This is the behavior of posix mode
5585                      through version 4.1.  The default bash behavior  remains
5586                      as in previous versions.
5587              compat42
5588                      If  set, bash does not process the replacement string in
5589                      the pattern  substitution  word  expansion  using  quote
5590                      removal.
5591              compat43
5592                      If  set,  bash  does  not  print a warning message if an
5593                      attempt is made to use a quoted compound  array  assign‐
5594                      ment  as  an  argument  to declare, makes word expansion
5595                      errors non-fatal errors that cause the  current  command
5596                      to  fail  (the  default  behavior  is to make them fatal
5597                      errors that cause the shell to exit), and does not reset
5598                      the  loop  state when a shell function is executed (this
5599                      allows break or continue in a shell function  to  affect
5600                      loops in the caller's context).
5601              compat44
5602                      If   set,   bash  saves  the  positional  parameters  to
5603                      BASH_ARGV and BASH_ARGC before they are used, regardless
5604                      of whether or not extended debugging mode is enabled.
5605              complete_fullquote
5606                      If  set,  bash  quotes all shell metacharacters in file‐
5607                      names and directory names  when  performing  completion.
5608                      If not set, bash removes metacharacters such as the dol‐
5609                      lar sign from the set of characters that will be  quoted
5610                      in  completed filenames when these metacharacters appear
5611                      in shell variable references in words to  be  completed.
5612                      This  means  that  dollar  signs  in variable names that
5613                      expand to directories will not be quoted;  however,  any
5614                      dollar  signs appearing in filenames will not be quoted,
5615                      either.  This is active only when bash  is  using  back‐
5616                      slashes  to quote completed filenames.  This variable is
5617                      set by default, which is the default  bash  behavior  in
5618                      versions through 4.2.
5619              direxpand
5620                      If  set,  bash replaces directory names with the results
5621                      of word expansion when performing  filename  completion.
5622                      This  changes  the contents of the readline editing buf‐
5623                      fer.  If not set, bash attempts  to  preserve  what  the
5624                      user typed.
5625              dirspell
5626                      If  set,  bash attempts spelling correction on directory
5627                      names during word completion if the directory name  ini‐
5628                      tially supplied does not exist.
5629              dotglob If  set, bash includes filenames beginning with a `.' in
5630                      the results of pathname expansion.  The filenames  ``.''
5631                      and  ``..''   must always be matched explicitly, even if
5632                      dotglob is set.
5633              execfail
5634                      If set, a non-interactive shell will not exit if it can‐
5635                      not  execute  the  file  specified as an argument to the
5636                      exec builtin command.  An  interactive  shell  does  not
5637                      exit if exec fails.
5638              expand_aliases
5639                      If  set,  aliases  are expanded as described above under
5640                      ALIASES.  This option is enabled by default for interac‐
5641                      tive shells.
5642              extdebug
5643                      If  set  at  shell  invocation,  arrange  to execute the
5644                      debugger profile before the shell starts,  identical  to
5645                      the  --debugger option.  If set after invocation, behav‐
5646                      ior intended for use by debuggers is enabled:
5647                      1.     The -F option to the declare builtin displays the
5648                             source file name and line number corresponding to
5649                             each function name supplied as an argument.
5650                      2.     If the command run by the DEBUG  trap  returns  a
5651                             non-zero  value,  the next command is skipped and
5652                             not executed.
5653                      3.     If the command run by the DEBUG  trap  returns  a
5654                             value  of 2, and the shell is executing in a sub‐
5655                             routine (a shell function or a shell script  exe‐
5656                             cuted  by  the  .  or source builtins), the shell
5657                             simulates a call to return.
5658                      4.     BASH_ARGC and BASH_ARGV are updated as  described
5659                             in their descriptions above.
5660                      5.     Function  tracing  is  enabled: command substitu‐
5661                             tion, shell functions, and subshells invoked with
5662                             ( command ) inherit the DEBUG and RETURN traps.
5663                      6.     Error  tracing  is enabled: command substitution,
5664                             shell functions, and  subshells  invoked  with  (
5665                             command ) inherit the ERR trap.
5666              extglob If set, the extended pattern matching features described
5667                      above under Pathname Expansion are enabled.
5668              extquote
5669                      If set, $'string' and  $"string"  quoting  is  performed
5670                      within   ${parameter}   expansions  enclosed  in  double
5671                      quotes.  This option is enabled by default.
5672              failglob
5673                      If set, patterns which fail to  match  filenames  during
5674                      pathname expansion result in an expansion error.
5675              force_fignore
5676                      If  set,  the  suffixes  specified  by the FIGNORE shell
5677                      variable cause words to be ignored when performing  word
5678                      completion even if the ignored words are the only possi‐
5679                      ble  completions.   See  SHELL  VARIABLES  above  for  a
5680                      description  of  FIGNORE.   This  option  is  enabled by
5681                      default.
5682              globasciiranges
5683                      If set,  range  expressions  used  in  pattern  matching
5684                      bracket  expressions (see Pattern Matching above) behave
5685                      as if in the traditional C locale when  performing  com‐
5686                      parisons.   That  is,  the  current  locale's  collating
5687                      sequence is not taken into account, so b will  not  col‐
5688                      late  between  A  and  B,  and upper-case and lower-case
5689                      ASCII characters will collate together.
5690              globstar
5691                      If set, the pattern ** used in a pathname expansion con‐
5692                      text  will  match all files and zero or more directories
5693                      and subdirectories.  If the pattern is followed by a  /,
5694                      only directories and subdirectories match.
5695              gnu_errfmt
5696                      If set, shell error messages are written in the standard
5697                      GNU error message format.
5698              histappend
5699                      If set, the history list is appended to the  file  named
5700                      by  the  value  of  the HISTFILE variable when the shell
5701                      exits, rather than overwriting the file.
5702              histreedit
5703                      If set, and readline is being used, a user is given  the
5704                      opportunity to re-edit a failed history substitution.
5705              histverify
5706                      If  set, and readline is being used, the results of his‐
5707                      tory substitution are  not  immediately  passed  to  the
5708                      shell  parser.   Instead,  the  resulting line is loaded
5709                      into the readline editing buffer, allowing further modi‐
5710                      fication.
5711              hostcomplete
5712                      If set, and readline is being used, bash will attempt to
5713                      perform hostname completion when a word containing  a  @
5714                      is   being  completed  (see  Completing  under  READLINE
5715                      above).  This is enabled by default.
5716              huponexit
5717                      If set, bash will send SIGHUP to all jobs when an inter‐
5718                      active login shell exits.
5719              inherit_errexit
5720                      If  set,  command substitution inherits the value of the
5721                      errexit option, instead of unsetting it in the  subshell
5722                      environment.   This option is enabled when posix mode is
5723                      enabled.
5724              interactive_comments
5725                      If set, allow a word beginning with # to cause that word
5726                      and  all remaining characters on that line to be ignored
5727                      in an interactive  shell  (see  COMMENTS  above).   This
5728                      option is enabled by default.
5729              lastpipe
5730                      If  set,  and  job control is not active, the shell runs
5731                      the last command of a pipeline not executed in the back‐
5732                      ground in the current shell environment.
5733              lithist If  set,  and  the cmdhist option is enabled, multi-line
5734                      commands are saved to the history with embedded newlines
5735                      rather than using semicolon separators where possible.
5736              localvar_inherit
5737                      If set, local variables inherit the value and attributes
5738                      of a variable of the same name that exists at a previous
5739                      scope  before  any  new  value is assigned.  The nameref
5740                      attribute is not inherited.
5741              localvar_unset
5742                      If set, calling unset on  local  variables  in  previous
5743                      function  scopes  marks  them so subsequent lookups find
5744                      them unset until that function returns. This is  identi‐
5745                      cal  to the behavior of unsetting local variables at the
5746                      current function scope.
5747              login_shell
5748                      The shell sets this option if it is started as  a  login
5749                      shell  (see  INVOCATION  above).   The  value may not be
5750                      changed.
5751              mailwarn
5752                      If set, and a file that bash is checking  for  mail  has
5753                      been  accessed  since  the last time it was checked, the
5754                      message ``The mail in mailfile has been read''  is  dis‐
5755                      played.
5756              no_empty_cmd_completion
5757                      If  set,  and  readline  is  being  used,  bash will not
5758                      attempt to search the PATH for possible completions when
5759                      completion is attempted on an empty line.
5760              nocaseglob
5761                      If  set,  bash  matches  filenames in a case-insensitive
5762                      fashion when performing pathname expansion (see Pathname
5763                      Expansion above).
5764              nocasematch
5765                      If  set,  bash  matches  patterns  in a case-insensitive
5766                      fashion when performing matching while executing case or
5767                      [[ conditional commands, when performing pattern substi‐
5768                      tution word expansions, or when filtering possible  com‐
5769                      pletions as part of programmable completion.
5770              nullglob
5771                      If  set,  bash allows patterns which match no files (see
5772                      Pathname Expansion above) to expand to  a  null  string,
5773                      rather than themselves.
5774              progcomp
5775                      If set, the programmable completion facilities (see Pro‐
5776                      grammable Completion above) are enabled.  This option is
5777                      enabled by default.
5778              progcomp_alias
5779                      If  set,  and  programmable  completion is enabled, bash
5780                      treats a command name that doesn't have any  completions
5781                      as  a possible alias and attempts alias expansion. If it
5782                      has an  alias,  bash  attempts  programmable  completion
5783                      using  the  command  word  resulting  from  the expanded
5784                      alias.
5785              promptvars
5786                      If set, prompt strings undergo parameter expansion, com‐
5787                      mand   substitution,  arithmetic  expansion,  and  quote
5788                      removal after being expanded as described  in  PROMPTING
5789                      above.  This option is enabled by default.
5790              restricted_shell
5791                      The   shell  sets  this  option  if  it  is  started  in
5792                      restricted mode (see RESTRICTED SHELL below).  The value
5793                      may  not be changed.  This is not reset when the startup
5794                      files are executed, allowing the startup files  to  dis‐
5795                      cover whether or not a shell is restricted.
5796              shift_verbose
5797                      If  set,  the shift builtin prints an error message when
5798                      the shift count exceeds the number of positional parame‐
5799                      ters.
5800              sourcepath
5801                      If set, the source (.) builtin uses the value of PATH to
5802                      find the directory containing the file  supplied  as  an
5803                      argument.  This option is enabled by default.
5804              xpg_echo
5805                      If   set,  the  echo  builtin  expands  backslash-escape
5806                      sequences by default.
5807
5808       suspend [-f]
5809              Suspend the execution of this shell until it receives a  SIGCONT
5810              signal.  A login shell cannot be suspended; the -f option can be
5811              used to override this and force the suspension.  The return sta‐
5812              tus  is  0  unless the shell is a login shell and -f is not sup‐
5813              plied, or if job control is not enabled.
5814
5815       test expr
5816       [ expr ]
5817              Return a status of 0 (true) or 1 (false) depending on the evalu‐
5818              ation of the conditional expression expr.  Each operator and op‐
5819              erand must be a separate argument.  Expressions are composed  of
5820              the  primaries  described  above  under CONDITIONAL EXPRESSIONS.
5821              test does not accept any options, nor does it accept and  ignore
5822              an argument of -- as signifying the end of options.
5823
5824              Expressions  may  be  combined  using  the  following operators,
5825              listed  in  decreasing  order  of  precedence.   The  evaluation
5826              depends  on the number of arguments; see below.  Operator prece‐
5827              dence is used when there are five or more arguments.
5828              ! expr True if expr is false.
5829              ( expr )
5830                     Returns the value of expr.  This may be used to  override
5831                     the normal precedence of operators.
5832              expr1 -a expr2
5833                     True if both expr1 and expr2 are true.
5834              expr1 -o expr2
5835                     True if either expr1 or expr2 is true.
5836
5837              test and [ evaluate conditional expressions using a set of rules
5838              based on the number of arguments.
5839
5840              0 arguments
5841                     The expression is false.
5842              1 argument
5843                     The expression is true if and only if the argument is not
5844                     null.
5845              2 arguments
5846                     If the first argument is !, the expression is true if and
5847                     only if the second argument is null.  If the first  argu‐
5848                     ment  is  one  of  the unary conditional operators listed
5849                     above under CONDITIONAL EXPRESSIONS,  the  expression  is
5850                     true if the unary test is true.  If the first argument is
5851                     not a valid unary conditional operator, the expression is
5852                     false.
5853              3 arguments
5854                     The following conditions are applied in the order listed.
5855                     If the second argument is one of the  binary  conditional
5856                     operators listed above under CONDITIONAL EXPRESSIONS, the
5857                     result of the expression is the result of the binary test
5858                     using  the first and third arguments as operands.  The -a
5859                     and -o operators are  considered  binary  operators  when
5860                     there  are  three arguments.  If the first argument is !,
5861                     the value is the negation of the two-argument test  using
5862                     the second and third arguments.  If the first argument is
5863                     exactly ( and the third argument is exactly ), the result
5864                     is  the one-argument test of the second argument.  Other‐
5865                     wise, the expression is false.
5866              4 arguments
5867                     If the first argument is !, the result is the negation of
5868                     the  three-argument  expression composed of the remaining
5869                     arguments.  Otherwise, the expression is parsed and eval‐
5870                     uated  according  to  precedence  using  the rules listed
5871                     above.
5872              5 or more arguments
5873                     The expression  is  parsed  and  evaluated  according  to
5874                     precedence using the rules listed above.
5875
5876              When  used  with  test  or [, the < and > operators sort lexico‐
5877              graphically using ASCII ordering.
5878
5879       times  Print the accumulated user and system times for  the  shell  and
5880              for processes run from the shell.  The return status is 0.
5881
5882       trap [-lp] [[arg] sigspec ...]
5883              The  command  arg  is  to  be  read  and executed when the shell
5884              receives signal(s) sigspec.  If arg is absent (and  there  is  a
5885              single  sigspec)  or  -,  each  specified signal is reset to its
5886              original disposition (the value it  had  upon  entrance  to  the
5887              shell).   If arg is the null string the signal specified by each
5888              sigspec is ignored by the shell and by the commands it  invokes.
5889              If  arg  is  not present and -p has been supplied, then the trap
5890              commands associated with each  sigspec  are  displayed.   If  no
5891              arguments  are  supplied or if only -p is given, trap prints the
5892              list of commands associated with each  signal.   The  -l  option
5893              causes  the shell to print a list of signal names and their cor‐
5894              responding numbers.   Each  sigspec  is  either  a  signal  name
5895              defined  in  <signal.h>,  or  a signal number.  Signal names are
5896              case insensitive and the SIG prefix is optional.
5897
5898              If a sigspec is EXIT (0) the command arg  is  executed  on  exit
5899              from  the shell.  If a sigspec is DEBUG, the command arg is exe‐
5900              cuted before every simple command, for  command,  case  command,
5901              select  command,  every  arithmetic  for command, and before the
5902              first command executes in a shell function  (see  SHELL  GRAMMAR
5903              above).   Refer to the description of the extdebug option to the
5904              shopt builtin for details of its effect on the DEBUG trap.  If a
5905              sigspec is RETURN, the command arg is executed each time a shell
5906              function or a script executed with the . or source builtins fin‐
5907              ishes executing.
5908
5909              If  a  sigspec  is  ERR,  the command arg is executed whenever a
5910              pipeline (which may consist of a single simple command), a list,
5911              or a compound command returns a non-zero exit status, subject to
5912              the following conditions.  The ERR trap is not executed  if  the
5913              failed command is part of the command list immediately following
5914              a while or until keyword, part of the test in an  if  statement,
5915              part of a command executed in a && or || list except the command
5916              following the final && or ||, any command in a pipeline but  the
5917              last,  or  if the command's return value is being inverted using
5918              !.  These are the same conditions obeyed  by  the  errexit  (-e)
5919              option.
5920
5921              Signals ignored upon entry to the shell cannot be trapped, reset
5922              or listed.  Trapped signals that are not being ignored are reset
5923              to  their  original values in a subshell or subshell environment
5924              when one is created.  The return status is false if any  sigspec
5925              is invalid; otherwise trap returns true.
5926
5927       type [-aftpP] name [name ...]
5928              With  no options, indicate how each name would be interpreted if
5929              used as a command name.  If the -t option is used, type prints a
5930              string  which  is  one  of alias, keyword, function, builtin, or
5931              file if  name  is  an  alias,  shell  reserved  word,  function,
5932              builtin,  or disk file, respectively.  If the name is not found,
5933              then nothing  is  printed,  and  an  exit  status  of  false  is
5934              returned.   If  the  -p  option is used, type either returns the
5935              name of the disk file that would be executed if name were speci‐
5936              fied as a command name, or nothing if ``type -t name'' would not
5937              return file.  The -P option forces a PATH search for each  name,
5938              even if ``type -t name'' would not return file.  If a command is
5939              hashed, -p and -P print the hashed value, which is not necessar‐
5940              ily  the  file  that appears first in PATH.  If the -a option is
5941              used, type prints all of the places that contain  an  executable
5942              named name.  This includes aliases and functions, if and only if
5943              the -p option is not also used.  The table of hashed commands is
5944              not  consulted  when  using  -a.  The -f option suppresses shell
5945              function lookup, as with the command builtin.  type returns true
5946              if all of the arguments are found, false if any are not found.
5947
5948       ulimit [-HSabcdefiklmnpqrstuvxPT [limit]]
5949              Provides  control  over the resources available to the shell and
5950              to processes started by it, on systems that allow such  control.
5951              The -H and -S options specify that the hard or soft limit is set
5952              for the given resource.  A hard limit cannot be increased  by  a
5953              non-root  user  once it is set; a soft limit may be increased up
5954              to the value of the hard limit.  If neither -H nor -S is  speci‐
5955              fied, both the soft and hard limits are set.  The value of limit
5956              can be a number in the unit specified for the resource or one of
5957              the special values hard, soft, or unlimited, which stand for the
5958              current hard limit,  the  current  soft  limit,  and  no  limit,
5959              respectively.   If  limit  is  omitted, the current value of the
5960              soft limit of the resource is printed, unless the -H  option  is
5961              given.  When more than one resource is specified, the limit name
5962              and unit are printed before the value.  Other options are inter‐
5963              preted as follows:
5964              -a     All current limits are reported
5965              -b     The maximum socket buffer size
5966              -c     The maximum size of core files created
5967              -d     The maximum size of a process's data segment
5968              -e     The maximum scheduling priority ("nice")
5969              -f     The  maximum  size  of files written by the shell and its
5970                     children
5971              -i     The maximum number of pending signals
5972              -k     The maximum number of kqueues that may be allocated
5973              -l     The maximum size that may be locked into memory
5974              -m     The maximum resident set size (many systems do not  honor
5975                     this limit)
5976              -n     The maximum number of open file descriptors (most systems
5977                     do not allow this value to be set)
5978              -p     The pipe size in 512-byte blocks (this may not be set)
5979              -q     The maximum number of bytes in POSIX message queues
5980              -r     The maximum real-time scheduling priority
5981              -s     The maximum stack size
5982              -t     The maximum amount of cpu time in seconds
5983              -u     The maximum number of processes  available  to  a  single
5984                     user
5985              -v     The  maximum  amount  of  virtual memory available to the
5986                     shell and, on some systems, to its children
5987              -x     The maximum number of file locks
5988              -P     The maximum number of pseudoterminals
5989              -T     The maximum number of threads
5990
5991              If limit is given, and the -a option is not used, limit  is  the
5992              new  value  of  the  specified resource.  If no option is given,
5993              then -f is assumed.  Values are in 1024-byte increments,  except
5994              for  -t,  which is in seconds; -p, which is in units of 512-byte
5995              blocks; -P, -T, -b, -k, -n, and -u, which are  unscaled  values;
5996              and, when in posix mode, -c and -f, which are in 512-byte incre‐
5997              ments.  The return status is 0 unless an invalid option or argu‐
5998              ment  is supplied, or an error occurs while setting a new limit.
5999              In POSIX Mode 512-byte blocks are used for  the  `-c'  and  `-f'
6000              options.
6001
6002       umask [-p] [-S] [mode]
6003              The user file-creation mask is set to mode.  If mode begins with
6004              a digit, it is interpreted as an octal number; otherwise  it  is
6005              interpreted  as a symbolic mode mask similar to that accepted by
6006              chmod(1).  If mode is omitted, the current value of the mask  is
6007              printed.   The  -S  option causes the mask to be printed in sym‐
6008              bolic form; the default output is an octal number.   If  the  -p
6009              option is supplied, and mode is omitted, the output is in a form
6010              that may be reused as input.  The return status is 0 if the mode
6011              was  successfully  changed  or if no mode argument was supplied,
6012              and false otherwise.
6013
6014       unalias [-a] [name ...]
6015              Remove each name from the list of defined  aliases.   If  -a  is
6016              supplied,  all  alias definitions are removed.  The return value
6017              is true unless a supplied name is not a defined alias.
6018
6019       unset [-fv] [-n] [name ...]
6020              For each name, remove the corresponding  variable  or  function.
6021              If the -v option is given, each name refers to a shell variable,
6022              and that variable is removed.  Read-only variables  may  not  be
6023              unset.   If  -f  is specified, each name refers to a shell func‐
6024              tion, and the function definition is removed.  If the -n  option
6025              is  supplied, and name is a variable with the nameref attribute,
6026              name will be unset rather than the variable it  references.   -n
6027              has  no  effect if the -f option is supplied.  If no options are
6028              supplied, each name refers to a variable; if there is  no  vari‐
6029              able  by  that name, any function with that name is unset.  Each
6030              unset variable or  function  is  removed  from  the  environment
6031              passed  to subsequent commands.  If any of COMP_WORDBREAKS, RAN‐
6032              DOM, SECONDS, LINENO, HISTCMD, FUNCNAME, GROUPS, or DIRSTACK are
6033              unset, they lose their special properties, even if they are sub‐
6034              sequently reset.  The exit status is true unless a name is read‐
6035              only.
6036
6037       wait [-fn] [id ...]
6038              Wait for each specified child process and return its termination
6039              status.  Each id may be a process ID or a job specification;  if
6040              a  job  spec  is given, all processes in that job's pipeline are
6041              waited for.  If id is not given, all currently active child pro‐
6042              cesses are waited for, and the return status is zero.  If the -n
6043              option is supplied, wait waits for  any  job  to  terminate  and
6044              returns  its exit status.  If the -f option is supplied, and job
6045              control is enabled, wait forces id to terminate before returning
6046              its  status, instead of returning when it changes status.  If id
6047              specifies a non-existent process or job, the  return  status  is
6048              127.   Otherwise,  the  return  status is the exit status of the
6049              last process or job waited for.
6050

RESTRICTED SHELL

6052       If bash is started with the name rbash, or the -r option is supplied at
6053       invocation,  the  shell becomes restricted.  A restricted shell is used
6054       to set up an environment more controlled than the standard  shell.   It
6055       behaves  identically  to bash with the exception that the following are
6056       disallowed or not performed:
6057
6058       ·      changing directories with cd
6059
6060       ·      setting or unsetting the values of SHELL, PATH, ENV, or BASH_ENV
6061
6062       ·      specifying command names containing /
6063
6064       ·      specifying a filename containing a / as an  argument  to  the  .
6065              builtin command
6066
6067       ·      specifying  a  filename containing a slash as an argument to the
6068              -p option to the hash builtin command
6069
6070       ·      importing function definitions from  the  shell  environment  at
6071              startup
6072
6073       ·      parsing  the  value  of  SHELLOPTS from the shell environment at
6074              startup
6075
6076       ·      redirecting output using the >, >|, <>, >&, &>, and >> redirect‐
6077              ion operators
6078
6079       ·      using the exec builtin command to replace the shell with another
6080              command
6081
6082       ·      adding or deleting builtin commands with the -f and  -d  options
6083              to the enable builtin command
6084
6085       ·      using  the  enable  builtin  command  to  enable  disabled shell
6086              builtins
6087
6088       ·      specifying the -p option to the command builtin command
6089
6090       ·      turning off restricted mode with set +r or set +o restricted.
6091
6092       These restrictions are enforced after any startup files are read.
6093
6094       When a command that is found to be a shell script is executed (see COM‐
6095       MAND  EXECUTION  above),  rbash turns off any restrictions in the shell
6096       spawned to execute the script.
6097

SEE ALSO

6099       Bash Reference Manual, Brian Fox and Chet Ramey
6100       The Gnu Readline Library, Brian Fox and Chet Ramey
6101       The Gnu History Library, Brian Fox and Chet Ramey
6102       Portable Operating System Interface (POSIX) Part 2:  Shell  and  Utili‐
6103       ties, IEEE --
6104              http://pubs.opengroup.org/onlinepubs/9699919799/
6105       http://tiswww.case.edu/~chet/bash/POSIX -- a description of posix mode
6106       sh(1), ksh(1), csh(1)
6107       emacs(1), vi(1)
6108       readline(3)
6109

FILES

6111       /bin/bash
6112              The bash executable
6113       /etc/profile
6114              The systemwide initialization file, executed for login shells
6115       /etc/bash.bash_logout
6116              The  systemwide  login shell cleanup file, executed when a login
6117              shell exits
6118       ~/.bash_profile
6119              The personal initialization file, executed for login shells
6120       ~/.bashrc
6121              The individual per-interactive-shell startup file
6122       ~/.bash_logout
6123              The individual login shell cleanup file, executed when  a  login
6124              shell exits
6125       ~/.inputrc
6126              Individual readline initialization file
6127

AUTHORS

6129       Brian Fox, Free Software Foundation
6130       bfox@gnu.org
6131
6132       Chet Ramey, Case Western Reserve University
6133       chet.ramey@case.edu
6134

BUG REPORTS

6136       If you find a bug in bash, you should report it.  But first, you should
6137       make sure that it really is a bug, and that it appears  in  the  latest
6138       version   of  bash.   The  latest  version  is  always  available  from
6139       ftp://ftp.gnu.org/pub/gnu/bash/.
6140
6141       Once you have determined that a bug actually exists,  use  the  bashbug
6142       command  to submit a bug report.  If you have a fix, you are encouraged
6143       to mail that as well!  Suggestions and `philosophical' bug reports  may
6144       be  mailed  to  bug-bash@gnu.org  or  posted  to  the  Usenet newsgroup
6145       gnu.bash.bug.
6146
6147       ALL bug reports should include:
6148
6149       The version number of bash
6150       The hardware and operating system
6151       The compiler used to compile
6152       A description of the bug behaviour
6153       A short script or `recipe' which exercises the bug
6154
6155       bashbug inserts the first three items automatically into  the  template
6156       it provides for filing a bug report.
6157
6158       Comments and bug reports concerning this manual page should be directed
6159       to chet.ramey@case.edu.
6160

BUGS

6162       It's too big and too slow.
6163
6164       There are some subtle differences between bash and traditional versions
6165       of sh, mostly because of the POSIX specification.
6166
6167       Aliases are confusing in some uses.
6168
6169       Shell builtin commands and functions are not stoppable/restartable.
6170
6171       Compound commands and command sequences of the form `a ; b ; c' are not
6172       handled gracefully  when  process  suspension  is  attempted.   When  a
6173       process  is stopped, the shell immediately executes the next command in
6174       the sequence.  It suffices to place the sequence  of  commands  between
6175       parentheses  to  force  it  into  a subshell, which may be stopped as a
6176       unit.
6177
6178       Array variables may not (yet) be exported.
6179
6180       There may be only one active coprocess at a time.
6181
6182
6183
6184GNU Bash 5.0                    2018 December 7                        BASH(1)
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