1ZSHMISC(1)                  General Commands Manual                 ZSHMISC(1)
2
3
4

NAME

6       zshmisc - everything and then some
7

SIMPLE COMMANDS & PIPELINES

9       A  simple  command is a sequence of optional parameter assignments fol‐
10       lowed by  blank-separated  words,  with  optional  redirections  inter‐
11       spersed.   For  a  description of assignment, see the beginning of zsh‐
12       param(1).
13
14       The first word is the command to be executed, and the remaining  words,
15       if  any, are arguments to the command.  If a command name is given, the
16       parameter assignments modify the environment of the command when it  is
17       executed.   The  value  of  a simple command is its exit status, or 128
18       plus the signal number if terminated by a signal.  For example,
19
20              echo foo
21
22       is a simple command with arguments.
23
24       A pipeline is either a simple command, or a sequence  of  two  or  more
25       simple commands where each command is separated from the next by `|' or
26       `|&'.  Where commands are separated by `|', the standard output of  the
27       first  command is connected to the standard input of the next.  `|&' is
28       shorthand for `2>&1 |', which connects both the standard output and the
29       standard  error  of the command to the standard input of the next.  The
30       value of a pipeline is the value of the last command, unless the  pipe‐
31       line  is preceded by `!' in which case the value is the logical inverse
32       of the value of the last command.  For example,
33
34              echo foo | sed 's/foo/bar/'
35
36       is a pipeline, where the output (`foo' plus a  newline)  of  the  first
37       command will be passed to the input of the second.
38
39       If a pipeline is preceded by `coproc', it is executed as a coprocess; a
40       two-way pipe is established between it and the parent shell.  The shell
41       can read from or write to the coprocess by means of the `>&p' and `<&p'
42       redirection operators or with `print -p' and  `read  -p'.   A  pipeline
43       cannot be preceded by both `coproc' and `!'.  If job control is active,
44       the coprocess can be treated in other than input and output as an ordi‐
45       nary background job.
46
47       A  sublist  is  either  a single pipeline, or a sequence of two or more
48       pipelines separated by `&&' or `||'.  If two pipelines are separated by
49       `&&',  the  second  pipeline  is  executed  only  if the first succeeds
50       (returns a zero status).  If two pipelines are separated by  `||',  the
51       second  is executed only if the first fails (returns a nonzero status).
52       Both operators have equal precedence and  are  left  associative.   The
53       value  of  the sublist is the value of the last pipeline executed.  For
54       example,
55
56              dmesg | grep panic && print yes
57
58       is a sublist consisting of two pipelines, the second just a simple com‐
59       mand  which  will be executed if and only if the grep command returns a
60       zero status.  If it does not, the value of the sublist is  that  return
61       status,  else  it is the status returned by the print (almost certainly
62       zero).
63
64       A list is a sequence of zero or more sublists, in which each sublist is
65       terminated  by `;', `&', `&|', `&!', or a newline.  This terminator may
66       optionally be omitted from the last sublist in the list when  the  list
67       appears as a complex command inside `(...)' or `{...}'.  When a sublist
68       is terminated by `;' or newline, the  shell  waits  for  it  to  finish
69       before  executing  the  next  sublist.  If a sublist is terminated by a
70       `&', `&|', or `&!', the shell executes the last pipeline in it  in  the
71       background,  and  does  not  wait for it to finish (note the difference
72       from other shells which execute the whole sublist in  the  background).
73       A backgrounded pipeline returns a status of zero.
74
75       More generally, a list can be seen as a set of any shell commands what‐
76       soever, including the complex commands below; this is implied  wherever
77       the  word  `list' appears in later descriptions.  For example, the com‐
78       mands in a shell function form a special sort of list.
79

PRECOMMAND MODIFIERS

81       A simple command may be preceded by a precommand modifier,  which  will
82       alter  how  the  command  is  interpreted.   These  modifiers are shell
83       builtin commands with the exception of nocorrect which  is  a  reserved
84       word.
85
86       -      The  command  is  executed  with  a `-' prepended to its argv[0]
87              string.
88
89       builtin
90              The command word is taken to be the name of a  builtin  command,
91              rather than a shell function or external command.
92
93       command [ -pvV ]
94              The command word is taken to be the name of an external command,
95              rather than a shell function or builtin.   If the POSIX_BUILTINS
96              option  is  set, builtins will also be executed but certain spe‐
97              cial properties of them are suppressed. The  -p  flag  causes  a
98              default  path  to be searched instead of that in $path. With the
99              -v flag, command is similar to whence and with -V, it is equiva‐
100              lent to whence -v.
101
102       exec [ -cl ] [ -a argv0 ]
103              The  following  command  together  with  any arguments is run in
104              place of the current process, rather than as a sub-process.  The
105              shell  does not fork and is replaced.  The shell does not invoke
106              TRAPEXIT, nor does it source zlogout  files.   The  options  are
107              provided for compatibility with other shells.
108
109              The -c option clears the environment.
110
111              The  -l  option  is  equivalent to the - precommand modifier, to
112              treat the replacement command as a login shell; the  command  is
113              executed  with  a  - prepended to its argv[0] string.  This flag
114              has no effect if used together with the -a option.
115
116              The -a option is used to specify explicitly the  argv[0]  string
117              (the  name  of  the command as seen by the process itself) to be
118              used by the replacement command and is  directly  equivalent  to
119              setting a value for the ARGV0 environment variable.
120
121       nocorrect
122              Spelling  correction is not done on any of the words.  This must
123              appear before any other precommand modifier,  as  it  is  inter‐
124              preted  immediately,  before  any  parsing  is  done.  It has no
125              effect in non-interactive shells.
126
127       noglob Filename generation (globbing) is not performed on  any  of  the
128              words.
129

COMPLEX COMMANDS

131       A complex command in zsh is one of the following:
132
133       if list then list [ elif list then list ] ... [ else list ] fi
134              The  if  list is executed, and if it returns a zero exit status,
135              the then list is executed.  Otherwise, the elif list is executed
136              and  if  its status is zero, the then list is executed.  If each
137              elif list returns nonzero status, the else list is executed.
138
139       for name ... [ in word ... ] term do list done
140              where term is at least one newline or ;.   Expand  the  list  of
141              words,  and set the parameter name to each of them in turn, exe‐
142              cuting list each time.  If the in word is omitted, use the posi‐
143              tional parameters instead of the words.
144
145              More  than  one  parameter  name  can  appear before the list of
146              words.  If N names are given, then on each execution of the loop
147              the  next  N words are assigned to the corresponding parameters.
148              If there are more names  than  remaining  words,  the  remaining
149              parameters  are  each set to the empty string.  Execution of the
150              loop ends when there is no remaining word to assign to the first
151              name.  It is only possible for in to appear as the first name in
152              the list, else it will be treated as  marking  the  end  of  the
153              list.
154
155       for (( [expr1] ; [expr2] ; [expr3] )) do list done
156              The arithmetic expression expr1 is evaluated first (see the sec‐
157              tion `Arithmetic Evaluation').  The arithmetic expression  expr2
158              is  repeatedly  evaluated  until  it  evaluates to zero and when
159              non-zero, list is executed and the arithmetic  expression  expr3
160              evaluated.   If any expression is omitted, then it behaves as if
161              it evaluated to 1.
162
163       while list do list done
164              Execute the do list as long as the while  list  returns  a  zero
165              exit status.
166
167       until list do list done
168              Execute the do list as long as until list returns a nonzero exit
169              status.
170
171       repeat word do list done
172              word is expanded and treated as an arithmetic expression,  which
173              must evaluate to a number n.  list is then executed n times.
174
175              The  repeat  syntax is disabled by default when the shell starts
176              in a mode emulating another shell.  It can be enabled  with  the
177              command `enable -r repeat'
178
179       case  word  in  [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ...
180       esac
181              Execute the list associated with the first pattern that  matches
182              word, if any.  The form of the patterns is the same as that used
183              for filename generation.  See the section `Filename Generation'.
184
185              Note further that, unless the SH_GLOB option is set,  the  whole
186              pattern  with alternatives is treated by the shell as equivalent
187              to a group of patterns within parentheses, although white  space
188              may  appear  about the parentheses and the vertical bar and will
189              be stripped from the pattern at those points.  White  space  may
190              appear  elsewhere  in the pattern; this is not stripped.  If the
191              SH_GLOB option is set, so that an  opening  parenthesis  can  be
192              unambiguously treated as part of the case syntax, the expression
193              is parsed into separate words and these are  treated  as  strict
194              alternatives (as in other shells).
195
196              If  the  list that is executed is terminated with ;& rather than
197              ;;, the following list is also executed.  The rule for the  ter‐
198              minator of the following list ;;, ;& or ;| is applied unless the
199              esac is reached.
200
201              If the list that is executed is terminated  with  ;|  the  shell
202              continues  to scan the patterns looking for the next match, exe‐
203              cuting the corresponding list, and applying  the  rule  for  the
204              corresponding  terminator  ;;,  ;& or ;|.  Note that word is not
205              re-expanded; all applicable patterns are tested  with  the  same
206              word.
207
208       select name [ in word ... term ] do list done
209              where  term  is one or more newline or ; to terminate the words.
210              Print the set of words, each preceded by a number.   If  the  in
211              word  is  omitted,  use  the positional parameters.  The PROMPT3
212              prompt is printed and a line is read from the line editor if the
213              shell is interactive and that is active, or else standard input.
214              If this line consists of the number of one of the listed  words,
215              then the parameter name is set to the word corresponding to this
216              number.  If this line is empty, the selection  list  is  printed
217              again.   Otherwise,  the  value  of the parameter name is set to
218              null.  The contents of the line  read  from  standard  input  is
219              saved  in the parameter REPLY.  list is executed for each selec‐
220              tion until a break or end-of-file is encountered.
221
222       ( list )
223              Execute list in a subshell.  Traps set by the trap  builtin  are
224              reset to their default values while executing list.
225
226       { list }
227              Execute list.
228
229       { try-list } always { always-list }
230              First  execute  try-list.   Regardless of errors, or break, con‐
231              tinue, or return commands encountered within  try-list,  execute
232              always-list.   Execution  then  continues from the result of the
233              execution of try-list; in other words, any error, or break, con‐
234              tinue,  or  return  command  is treated in the normal way, as if
235              always-list were not  present.   The  two  chunks  of  code  are
236              referred to as the `try block' and the `always block'.
237
238              Optional  newlines  or  semicolons  may appear after the always;
239              note, however, that they may not appear  between  the  preceding
240              closing brace and the always.
241
242              An `error' in this context is a condition such as a syntax error
243              which causes the shell to abort execution of the  current  func‐
244              tion,  script,  or  list.   Syntax  errors encountered while the
245              shell is parsing the code do not cause  the  always-list  to  be
246              executed.   For  example, an erroneously constructed if block in
247              try-list would cause the shell to abort during parsing, so  that
248              always-list  would not be executed, while an erroneous substitu‐
249              tion such as ${*foo*} would cause a run-time error, after  which
250              always-list would be executed.
251
252              An  error  condition  can  be  tested and reset with the special
253              integer variable TRY_BLOCK_ERROR.  Outside  an  always-list  the
254              value  is  irrelevant,  but  it  is  initialised  to -1.  Inside
255              always-list, the  value  is  1  if  an  error  occurred  in  the
256              try-list,  else  0.   If  TRY_BLOCK_ERROR is set to 0 during the
257              always-list, the error  condition  caused  by  the  try-list  is
258              reset,  and  shell execution continues normally after the end of
259              always-list.  Altering the value during the try-list is not use‐
260              ful (unless this forms part of an enclosing always block).
261
262              Regardless  of TRY_BLOCK_ERROR, after the end of always-list the
263              normal shell status $? is  the  value  returned  from  try-list.
264              This   will   be  non-zero  if  there  was  an  error,  even  if
265              TRY_BLOCK_ERROR was set to zero.
266
267              The following executes the given code, ignoring  any  errors  it
268              causes.   This is an alternative to the usual convention of pro‐
269              tecting code by executing it in a subshell.
270
271                     {
272                         # code which may cause an error
273                       } always {
274                         # This code is executed regardless of the error.
275                         (( TRY_BLOCK_ERROR = 0 ))
276                     }
277                     # The error condition has been reset.
278
279              An exit command (or a return command executed at  the  outermost
280              function  level  of  a  script) encountered in try-list does not
281              cause the execution of always-list.  Instead,  the  shell  exits
282              immediately after any EXIT trap has been executed.
283
284       function word ... [ () ] [ term ] { list }
285       word ... () [ term ] { list }
286       word ... () [ term ] command
287              where term is one or more newline or ;.  Define a function which
288              is referenced by any one of word.  Normally, only  one  word  is
289              provided;  multiple  words  are  usually only useful for setting
290              traps.  The body of the function is the list between the  {  and
291              }.  See the section `Functions'.
292
293              If  the  option  SH_GLOB  is  set  for  compatibility with other
294              shells, then whitespace may appear between the  left  and  right
295              parentheses  when there is a single word;  otherwise, the paren‐
296              theses will be treated as forming a  globbing  pattern  in  that
297              case.
298
299              In  any of the forms above, a redirection may appear outside the
300              function body, for example
301
302                     func() { ... } 2>&1
303
304              The redirection is stored with the function and applied whenever
305              the  function is executed.  Any variables in the redirection are
306              expanded at the point the function is executed, but outside  the
307              function scope.
308
309       time [ pipeline ]
310              The  pipeline is executed, and timing statistics are reported on
311              the standard error in the form specified by the TIMEFMT  parame‐
312              ter.   If  pipeline is omitted, print statistics about the shell
313              process and its children.
314
315       [[ exp ]]
316              Evaluates the conditional expression exp and return a zero  exit
317              status if it is true.  See the section `Conditional Expressions'
318              for a description of exp.
319

ALTERNATE FORMS FOR COMPLEX COMMANDS

321       Many of  zsh's  complex  commands  have  alternate  forms.   These  are
322       non-standard  and  are  likely not to be obvious even to seasoned shell
323       programmers; they should not be used anywhere that portability of shell
324       code is a concern.
325
326       The short versions below only work if sublist is of the form `{ list }'
327       or if the SHORT_LOOPS option is set.  For the if, while and until  com‐
328       mands, in both these cases the test part of the loop must also be suit‐
329       ably delimited, such as by `[[ ... ]]' or `(( ... ))', else the end  of
330       the  test will not be recognized.  For the for, repeat, case and select
331       commands no such special form for the arguments is necessary,  but  the
332       other  condition (the special form of sublist or use of the SHORT_LOOPS
333       option) still applies.
334
335       if list { list } [ elif list { list } ] ... [ else { list } ]
336              An alternate form of if.  The rules mean that
337
338                     if [[ -o ignorebraces ]] {
339                       print yes
340                     }
341
342              works, but
343
344                     if true {  # Does not work!
345                       print yes
346                     }
347
348              does not, since the test is not suitably delimited.
349
350       if list sublist
351              A short form of the alternate if.  The same limitations  on  the
352              form of list apply as for the previous form.
353
354       for name ... ( word ... ) sublist
355              A short form of for.
356
357       for name ... [ in word ... ] term sublist
358              where  term is at least one newline or ;.  Another short form of
359              for.
360
361       for (( [expr1] ; [expr2] ; [expr3] )) sublist
362              A short form of the arithmetic for command.
363
364       foreach name ... ( word ... ) list end
365              Another form of for.
366
367       while list { list }
368              An alternative form of while.  Note the limitations on the  form
369              of list mentioned above.
370
371       until list { list }
372              An  alternative form of until.  Note the limitations on the form
373              of list mentioned above.
374
375       repeat word sublist
376              This is a short form of repeat.
377
378       case word { [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ... }
379              An alternative form of case.
380
381       select name [ in word ... term ] sublist
382              where term is at least one  newline  or  ;.   A  short  form  of
383              select.
384
385       function word ... [ () ] [ term ] sublist
386              This is a short form of function.
387

RESERVED WORDS

389       The  following  words are recognized as reserved words when used as the
390       first word of a command unless quoted or disabled using disable -r:
391
392       do done esac then elif else fi for case if while function  repeat  time
393       until select coproc nocorrect foreach end ! [[ { } declare export float
394       integer local readonly typeset
395
396       Additionally,  `}'  is  recognized  in  any  position  if  neither  the
397       IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.
398

ERRORS

400       Certain  errors  are  treated  as fatal by the shell: in an interactive
401       shell, they cause control to return to  the  command  line,  and  in  a
402       non-interactive  shell  they  cause  the shell to be aborted.  In older
403       versions of zsh, a non-interactive shell running  a  script  would  not
404       abort  completely, but would resume execution at the next command to be
405       read from the script, skipping the remainder of any functions or  shell
406       constructs  such as loops or conditions; this somewhat illogical behav‐
407       iour can be recovered by setting the option CONTINUE_ON_ERROR.
408
409       Fatal errors found in non-interactive shells include:
410
411       ·      Failure to parse shell options passed when invoking the shell
412
413       ·      Failure to change options with the set builtin
414
415       ·      Parse errors of all sorts, including failures to parse mathemat‐
416              ical expressions
417
418       ·      Failures  to  set  or  modify  variable  behaviour with typeset,
419              local, declare, export, integer, float
420
421       ·      Execution of  incorrectly  positioned  loop  control  structures
422              (continue, break)
423
424       ·      Attempts  to  use  regular expression with no regular expression
425              module available
426
427       ·      Disallowed operations when the RESTRICTED options is set
428
429       ·      Failure to create a pipe needed for a pipeline
430
431       ·      Failure to create a multio
432
433       ·      Failure to autoload a module needed for a declared shell feature
434
435       ·      Errors creating command or process substitutions
436
437       ·      Syntax errors in glob qualifiers
438
439       ·      File generation errors where not caught by the  option  BAD_PAT‐
440              TERN
441
442       ·      All bad patterns used for matching within case statements
443
444       ·      File generation failures where not caused by NO_MATCH or similar
445              options
446
447       ·      All file generation errors where the pattern was used to  create
448              a multio
449
450       ·      Memory errors where detected by the shell
451
452       ·      Invalid subscripts to shell variables
453
454       ·      Attempts to assign read-only variables
455
456       ·      Logical  errors  with  variables such as assignment to the wrong
457              type
458
459       ·      Use of invalid variable names
460
461       ·      Errors in variable substitution syntax
462
463       ·      Failure to convert characters in $'...' expressions
464
465       If the POSIX_BUILTINS option is set, more errors associated with  shell
466       builtin  commands are treated as fatal, as specified by the POSIX stan‐
467       dard.
468

COMMENTS

470       In non-interactive shells, or in interactive shells with  the  INTERAC‐
471       TIVE_COMMENTS  option set, a word beginning with the third character of
472       the histchars parameter (`#' by default) causes that word and  all  the
473       following characters up to a newline to be ignored.
474

ALIASING

476       Every eligible word in the shell input is checked to see if there is an
477       alias defined for it.  If so, it is replaced by the text of  the  alias
478       if it is in command position (if it could be the first word of a simple
479       command), or if the alias is global.  If the replacement text ends with
480       a  space,  the next word in the shell input is always eligible for pur‐
481       poses of alias expansion.  An alias is defined using the alias builtin;
482       global aliases may be defined using the -g option to that builtin.
483
484       A word is defined as:
485
486       ·      Any plain string or glob pattern
487
488       ·      Any  quoted  string,  using  any  quoting  method (note that the
489              quotes must be part of the alias definition for this to be  eli‐
490              gible)
491
492       ·      Any parameter reference or command substitution
493
494       ·      Any  series of the foregoing, concatenated without whitespace or
495              other tokens between them
496
497       ·      Any reserved word (case, do, else, etc.)
498
499       ·      With global aliasing, any  command  separator,  any  redirection
500              operator, and `(' or `)' when not part of a glob pattern
501
502       Alias  expansion  is done on the shell input before any other expansion
503       except history expansion.  Therefore, if an alias is  defined  for  the
504       word  foo,  alias expansion may be avoided by quoting part of the word,
505       e.g. \foo.  Any form of quoting works, although  there  is  nothing  to
506       prevent  an  alias  being  defined  for the quoted form such as \foo as
507       well.
508
509       When POSIX_ALIASES is set, only plain unquoted strings are eligible for
510       aliasing.   The  alias  builtin does not reject ineligible aliases, but
511       they are not expanded.
512
513       For use with completion, which would remove an initial  backslash  fol‐
514       lowed  by  a character that isn't special, it may be more convenient to
515       quote the word by starting with a single quote, i.e.  'foo;  completion
516       will automatically add the trailing single quote.
517
518   Alias difficulties
519       Although aliases can be used in ways that bend normal shell syntax, not
520       every string of non-white-space characters can be used as an alias.
521
522       Any set of characters not listed as a word above is not a  word,  hence
523       no  attempt  is  made  to  expand  it  as an alias, no matter how it is
524       defined  (i.e.  via  the  builtin  or  the  special  parameter  aliases
525       described  in  the  section THE ZSH/PARAMETER MODULE in zshmodules(1)).
526       However, as noted in the case of POSIX_ALIASES above,  the  shell  does
527       not  attempt  to deduce whether the string corresponds to a word at the
528       time the alias is created.
529
530       For example, an expression containing an = at the start  of  a  command
531       line  is  an assignment and cannot be expanded as an alias; a lone = is
532       not an assignment but can only be set as an alias using the  parameter,
533       as otherwise the = is taken part of the syntax of the builtin command.
534
535       It  is  not  presently possible to alias the `((' token that introduces
536       arithmetic expressions, because until a full statement has been parsed,
537       it  cannot be distinguished from two consecutive `(' tokens introducing
538       nested subshells.  Also, if a separator such  as  &&  is  aliased,  \&&
539       turns into the two tokens \& and &, each of which may have been aliased
540       separately.  Similarly for \<<, \>|, etc.
541
542       There is a commonly encountered problem with aliases illustrated by the
543       following code:
544
545              alias echobar='echo bar'; echobar
546
547       This  prints  a  message  that  the command echobar could not be found.
548       This happens because aliases are expanded when the code is read in; the
549       entire  line  is read in one go, so that when echobar is executed it is
550       too late to expand the newly defined alias.  This is often a problem in
551       shell scripts, functions, and code executed with `source' or `.'.  Con‐
552       sequently, use of functions  rather  than  aliases  is  recommended  in
553       non-interactive code.
554
555       Note  also  the  unhelpful  interaction of aliases and function defini‐
556       tions:
557
558              alias func='noglob func'
559              func() {
560                  echo Do something with $*
561              }
562
563       Because aliases are expanded in function definitions, this  causes  the
564       following command to be executed:
565
566              noglob func() {
567                  echo Do something with $*
568              }
569
570       which  defines noglob as well as func as functions with the body given.
571       To avoid this, either quote the name func or use the alternative  func‐
572       tion  definition  form  `function func'.  Ensuring the alias is defined
573       after the function works but is problematic if the code fragment  might
574       be re-executed.
575

QUOTING

577       A  character  may be quoted (that is, made to stand for itself) by pre‐
578       ceding it with a `\'.  `\' followed by a newline is ignored.
579
580       A string enclosed between `$'' and `'' is processed the same way as the
581       string arguments of the print builtin, and the resulting string is con‐
582       sidered to be entirely quoted.  A literal `'' character can be included
583       in the string by using the `\'' escape.
584
585       All  characters  enclosed  between a pair of single quotes ('') that is
586       not preceded by a `$' are quoted.  A single quote cannot appear  within
587       single  quotes unless the option RC_QUOTES is set, in which case a pair
588       of single quotes are turned into a single quote.  For example,
589
590              print ''''
591
592       outputs nothing apart from a newline if RC_QUOTES is not set,  but  one
593       single quote if it is set.
594
595       Inside  double  quotes  (""), parameter and command substitution occur,
596       and `\' quotes the characters `\', ``', `"', `$', and the first charac‐
597       ter of $histchars (default `!').
598

REDIRECTION

600       If  a  command is followed by & and job control is not active, then the
601       default standard input for the command is  the  empty  file  /dev/null.
602       Otherwise,  the environment for the execution of a command contains the
603       file descriptors of the invoking  shell  as  modified  by  input/output
604       specifications.
605
606       The following may appear anywhere in a simple command or may precede or
607       follow a complex command.  Expansion occurs before  word  or  digit  is
608       used except as noted below.  If the result of substitution on word pro‐
609       duces more than one filename,  redirection  occurs  for  each  separate
610       filename in turn.
611
612       < word Open file word for reading as standard input.
613
614       <> word
615              Open  file  word  for reading and writing as standard input.  If
616              the file does not exist then it is created.
617
618       > word Open file word for writing as standard output.  If the file does
619              not exist then it is created.  If the file exists, and the CLOB‐
620              BER option is unset, this causes  an  error;  otherwise,  it  is
621              truncated to zero length.
622
623       >| word
624       >! word
625              Same  as  >, except that the file is truncated to zero length if
626              it exists, even if CLOBBER is unset.
627
628       >> word
629              Open file word for writing in append mode  as  standard  output.
630              If  the  file  does  not exist, and the CLOBBER option is unset,
631              this causes an error; otherwise, the file is created.
632
633       >>| word
634       >>! word
635              Same as >>, except that the file  is  created  if  it  does  not
636              exist, even if CLOBBER is unset.
637
638       <<[-] word
639              The  shell  input is read up to a line that is the same as word,
640              or to an end-of-file.  No parameter expansion, command substitu‐
641              tion or filename generation is performed on word.  The resulting
642              document, called a here-document, becomes the standard input.
643
644              If any character of word is quoted with single or double  quotes
645              or a `\', no interpretation is placed upon the characters of the
646              document.  Otherwise, parameter and command substitution occurs,
647              `\'  followed  by  a newline is removed, and `\' must be used to
648              quote the characters `\', `$', ``' and the  first  character  of
649              word.
650
651              Note  that  word itself does not undergo shell expansion.  Back‐
652              quotes in word do not have  their  usual  effect;  instead  they
653              behave  similarly  to  double quotes, except that the backquotes
654              themselves are passed through unchanged.  (This  information  is
655              given for completeness and it is not recommended that backquotes
656              be used.)  Quotes in the form $'...' have their standard  effect
657              of expanding backslashed references to special characters.
658
659              If <<- is used, then all leading tabs are stripped from word and
660              from the document.
661
662       <<< word
663              Perform shell expansion on word and pass the result to  standard
664              input.  This is known as a here-string.  Compare the use of word
665              in here-documents above,  where  word  does  not  undergo  shell
666              expansion.
667
668       <& number
669       >& number
670              The  standard  input/output  is  duplicated from file descriptor
671              number (see dup2(2)).
672
673       <& -
674       >& -   Close the standard input/output.
675
676       <& p
677       >& p   The input/output from/to the coprocess is moved to the  standard
678              input/output.
679
680       >& word
681       &> word
682              (Except  where `>& word' matches one of the above syntaxes; `&>'
683              can always be used to avoid  this  ambiguity.)   Redirects  both
684              standard  output  and  standard error (file descriptor 2) in the
685              manner of `> word'.  Note that  this  does  not  have  the  same
686              effect as `> word 2>&1' in the presence of multios (see the sec‐
687              tion below).
688
689       >&| word
690       >&! word
691       &>| word
692       &>! word
693              Redirects both standard output and standard error (file descrip‐
694              tor 2) in the manner of `>| word'.
695
696       >>& word
697       &>> word
698              Redirects both standard output and standard error (file descrip‐
699              tor 2) in the manner of `>> word'.
700
701       >>&| word
702       >>&! word
703       &>>| word
704       &>>! word
705              Redirects both standard output and standard error (file descrip‐
706              tor 2) in the manner of `>>| word'.
707
708       If  one  of  the above is preceded by a digit, then the file descriptor
709       referred to is that specified by the digit instead of the default 0  or
710       1.   The order in which redirections are specified is significant.  The
711       shell evaluates each redirection in  terms  of  the  (file  descriptor,
712       file) association at the time of evaluation.  For example:
713
714              ... 1>fname 2>&1
715
716       first associates file descriptor 1 with file fname.  It then associates
717       file descriptor 2 with the file associated with file descriptor 1 (that
718       is,  fname).  If the order of redirections were reversed, file descrip‐
719       tor 2 would be associated with the terminal (assuming file descriptor 1
720       had  been)  and  then  file  descriptor 1 would be associated with file
721       fname.
722
723       The `|&' command separator described in Simple Commands & Pipelines  in
724       zshmisc(1) is a shorthand for `2>&1 |'.
725
726       The various forms of process substitution, `<(list)', and `=(list)' for
727       input and `>(list)' for output, are often used together with  redirect‐
728       ion.   For  example,  if  word  in an output redirection is of the form
729       `>(list)' then the output is piped to the command represented by  list.
730       See Process Substitution in zshexpn(1).
731

OPENING FILE DESCRIPTORS USING PARAMETERS

733       When  the shell is parsing arguments to a command, and the shell option
734       IGNORE_BRACES is not set, a different form of redirection  is  allowed:
735       instead  of  a digit before the operator there is a valid shell identi‐
736       fier enclosed in braces.  The shell will open  a  new  file  descriptor
737       that is guaranteed to be at least 10 and set the parameter named by the
738       identifier to the file descriptor opened.   No  whitespace  is  allowed
739       between the closing brace and the redirection character.  For example:
740
741              ... {myfd}>&1
742
743       This opens a new file descriptor that is a duplicate of file descriptor
744       1 and sets the parameter myfd to the number  of  the  file  descriptor,
745       which  will  be at least 10.  The new file descriptor can be written to
746       using the syntax >&$myfd.
747
748       The syntax {varid}>&-, for example {myfd}>&-, may be used  to  close  a
749       file  descriptor opened in this fashion.  Note that the parameter given
750       by varid must previously be set to a file descriptor in this case.
751
752       It is an error to open or close a file descriptor in this fashion  when
753       the  parameter  is  readonly.   However,  it is not an error to read or
754       write a file descriptor using <&$param or >&$param if  param  is  read‐
755       only.
756
757       If  the option CLOBBER is unset, it is an error to open a file descrip‐
758       tor using a parameter that is already set to an  open  file  descriptor
759       previously allocated by this mechanism.  Unsetting the parameter before
760       using it for allocating a file descriptor avoids the error.
761
762       Note that this mechanism merely allocates or closes a file  descriptor;
763       it does not perform any redirections from or to it.  It is usually con‐
764       venient to allocate a file descriptor prior to use as  an  argument  to
765       exec.   The  syntax  does not in any case work when used around complex
766       commands such as parenthesised subshells or loops,  where  the  opening
767       brace  is  interpreted  as part of a command list to be executed in the
768       current shell.
769
770       The following shows a typical sequence of allocation, use, and  closing
771       of a file descriptor:
772
773              integer myfd
774              exec {myfd}>~/logs/mylogfile.txt
775              print This is a log message. >&$myfd
776              exec {myfd}>&-
777
778       Note  that  the  expansion  of  the  variable in the expression >&$myfd
779       occurs at the point the redirection  is  opened.   This  is  after  the
780       expansion  of  command arguments and after any redirections to the left
781       on the command line have been processed.
782

MULTIOS

784       If the user tries to open a file descriptor for writing more than once,
785       the  shell opens the file descriptor as a pipe to a process that copies
786       its input to all the specified outputs, similar to  tee,  provided  the
787       MULTIOS option is set, as it is by default.  Thus:
788
789              date >foo >bar
790
791       writes  the date to two files, named `foo' and `bar'.  Note that a pipe
792       is an implicit redirection; thus
793
794              date >foo | cat
795
796       writes the date to the file `foo', and also pipes it to cat.
797
798       Note also that redirections are always expanded in order.  This happens
799       regardless of the setting of the MULTIOS option, but with the option in
800       effect there are additional consequences. For example, the  meaning  of
801       the expression >&1 will change after a previous redirection:
802
803              date >&1 >output
804
805       In  the  case above, the >&1 refers to the standard output at the start
806       of the line; the result is similar to the tee command.   However,  con‐
807       sider:
808
809              date >output >&1
810
811       As redirections are evaluated in order, when the >&1 is encountered the
812       standard output is set to the file output and another copy of the  out‐
813       put  is  therefore  sent  to that file.  This is unlikely to be what is
814       intended.
815
816       If the MULTIOS option is set, the word after a redirection operator  is
817       also subjected to filename generation (globbing).  Thus
818
819              : > *
820
821       will  truncate  all files in the current directory, assuming there's at
822       least one.  (Without the MULTIOS option, it would create an empty  file
823       called `*'.)  Similarly, you can do
824
825              echo exit 0 >> *.sh
826
827       If the user tries to open a file descriptor for reading more than once,
828       the shell opens the file descriptor as a pipe to a process that  copies
829       all  the specified inputs to its output in the order specified, similar
830       to cat, provided the MULTIOS option is set.  Thus
831
832              sort <foo <fubar
833
834       or even
835
836              sort <f{oo,ubar}
837
838       is equivalent to `cat foo fubar | sort'.
839
840       Expansion of the redirection argument occurs at the point the redirect‐
841       ion  is  opened,  at the point described above for the expansion of the
842       variable in >&$myfd.
843
844       Note that a pipe is an implicit redirection; thus
845
846              cat bar | sort <foo
847
848       is equivalent to `cat bar foo | sort' (note the order of the inputs).
849
850       If the MULTIOS option is unset, each redirection replaces the  previous
851       redirection for that file descriptor.  However, all files redirected to
852       are actually opened, so
853
854              echo Hello > bar > baz
855
856       when MULTIOS is unset will  truncate  `bar',  and  write  `Hello'  into
857       `baz'.
858
859       There  is  a  problem  when an output multio is attached to an external
860       program.  A simple example shows this:
861
862              cat file >file1 >file2
863              cat file1 file2
864
865       Here, it is possible that the second `cat' will not  display  the  full
866       contents  of  file1  and  file2  (i.e.  the  original  contents of file
867       repeated twice).
868
869       The reason for this is that the  multios  are  spawned  after  the  cat
870       process  is  forked from the parent shell, so the parent shell does not
871       wait for the multios to finish writing data.  This means the command as
872       shown  can  exit  before  file1 and file2 are completely written.  As a
873       workaround, it is possible to run the cat process as part of a  job  in
874       the current shell:
875
876              { cat file } >file >file2
877
878       Here, the {...} job will pause to wait for both files to be written.
879

REDIRECTIONS WITH NO COMMAND

881       When a simple command consists of one or more redirection operators and
882       zero or more parameter assignments, but no command name, zsh can behave
883       in several ways.
884
885       If  the  parameter NULLCMD is not set or the option CSH_NULLCMD is set,
886       an error is caused.  This is the csh behavior and CSH_NULLCMD is set by
887       default when emulating csh.
888
889       If  the option SH_NULLCMD is set, the builtin `:' is inserted as a com‐
890       mand with the given redirections.  This is the default  when  emulating
891       sh or ksh.
892
893       Otherwise, if the parameter NULLCMD is set, its value will be used as a
894       command with the given redirections.  If both NULLCMD  and  READNULLCMD
895       are  set,  then the value of the latter will be used instead of that of
896       the former when the redirection is an input.  The default  for  NULLCMD
897       is `cat' and for READNULLCMD is `more'. Thus
898
899              < file
900
901       shows the contents of file on standard output, with paging if that is a
902       terminal.  NULLCMD and READNULLCMD may refer to shell functions.
903

COMMAND EXECUTION

905       If a command name contains no slashes, the shell attempts to locate it.
906       If  there exists a shell function by that name, the function is invoked
907       as described in the section  `Functions'.   If  there  exists  a  shell
908       builtin by that name, the builtin is invoked.
909
910       Otherwise,  the  shell  searches  each element of $path for a directory
911       containing an executable file by that name.  If the  search  is  unsuc‐
912       cessful,  the  shell prints an error message and returns a nonzero exit
913       status.
914
915       If execution fails because the file is not in  executable  format,  and
916       the  file  is  not  a  directory,  it  is assumed to be a shell script.
917       /bin/sh is spawned to execute it.  If the program is a  file  beginning
918       with `#!', the remainder of the first line specifies an interpreter for
919       the program.  The shell will execute the specified interpreter on oper‐
920       ating systems that do not handle this executable format in the kernel.
921
922       If  no  external command is found but a function command_not_found_han‐
923       dler exists the shell executes this  function  with  all  command  line
924       arguments.  The return status of the function becomes the status of the
925       command.  If the function wishes to mimic the behaviour  of  the  shell
926       when the command is not found, it should print the message `command not
927       found: cmd' to standard error and return status  127.   Note  that  the
928       handler  is  executed  in a subshell forked to execute an external com‐
929       mand, hence changes to directories,  shell  parameters,  etc.  have  no
930       effect on the main shell.
931

FUNCTIONS

933       Shell functions are defined with the function reserved word or the spe‐
934       cial syntax `funcname ()'.  Shell functions  are  read  in  and  stored
935       internally.  Alias names are resolved when the function is read.  Func‐
936       tions are executed like commands with the  arguments  passed  as  posi‐
937       tional parameters.  (See the section `Command Execution'.)
938
939       Functions execute in the same process as the caller and share all files
940       and present working directory with the caller.   A  trap  on  EXIT  set
941       inside a function is executed after the function completes in the envi‐
942       ronment of the caller.
943
944       The return builtin is used to return from function calls.
945
946       Function identifiers can be listed with the functions  builtin.   Func‐
947       tions can be undefined with the unfunction builtin.
948

AUTOLOADING FUNCTIONS

950       A  function  can  be marked as undefined using the autoload builtin (or
951       `functions -u' or `typeset -fu').  Such a function has no  body.   When
952       the  function  is first executed, the shell searches for its definition
953       using the elements of the fpath variable.  Thus to define functions for
954       autoloading, a typical sequence is:
955
956              fpath=(~/myfuncs $fpath)
957              autoload myfunc1 myfunc2 ...
958
959       The  usual  alias  expansion  during  reading will be suppressed if the
960       autoload builtin or its equivalent is given the option -U. This is rec‐
961       ommended  for  the use of functions supplied with the zsh distribution.
962       Note that for functions precompiled with the zcompile  builtin  command
963       the flag -U must be provided when the .zwc file is created, as the cor‐
964       responding information is compiled into the latter.
965
966       For each element in fpath, the shell looks for  three  possible  files,
967       the newest of which is used to load the definition for the function:
968
969       element.zwc
970              A  file  created  with  the  zcompile  builtin command, which is
971              expected to contain the definitions for  all  functions  in  the
972              directory named element.  The file is treated in the same manner
973              as a directory containing files for functions  and  is  searched
974              for  the  definition of the function.   If the definition is not
975              found, the search for a definition proceeds with the  other  two
976              possibilities described below.
977
978              If element already includes a .zwc extension (i.e. the extension
979              was explicitly given by the user), element is searched  for  the
980              definition  of the function without comparing its age to that of
981              other files; in fact, there does not need to  be  any  directory
982              named  element  without  the  suffix.  Thus including an element
983              such as `/usr/local/funcs.zwc' in fpath will speed up the search
984              for  functions,  with  the  disadvantage that functions included
985              must be explicitly recompiled by hand before the  shell  notices
986              any changes.
987
988       element/function.zwc
989              A  file  created with zcompile, which is expected to contain the
990              definition for function.  It may include other function  defini‐
991              tions as well, but those are neither loaded nor executed; a file
992              found in this way is searched only for the definition  of  func‐
993              tion.
994
995       element/function
996              A file of zsh command text, taken to be the definition for func‐
997              tion.
998
999       In summary, the order of searching is, first, in the parents of  direc‐
1000       tories  in  fpath  for  the  newer  of either a compiled directory or a
1001       directory in fpath; second, if more than one of these contains a  defi‐
1002       nition  for  the  function that is sought, the leftmost in the fpath is
1003       chosen; and third, within a directory, the newer of either  a  compiled
1004       function or an ordinary function definition is used.
1005
1006       If  the  KSH_AUTOLOAD option is set, or the file contains only a simple
1007       definition of the function, the file's contents will be executed.  This
1008       will  normally  define  the  function in question, but may also perform
1009       initialization, which is executed in the context of the function execu‐
1010       tion, and may therefore define local parameters.  It is an error if the
1011       function is not defined by loading the file.
1012
1013       Otherwise, the function body (with no surrounding  `funcname()  {...}')
1014       is taken to be the complete contents of the file.  This form allows the
1015       file to be used directly as an executable shell script.  If  processing
1016       of  the  file  results  in  the function being re-defined, the function
1017       itself is not re-executed.  To force the shell to  perform  initializa‐
1018       tion  and  then call the function defined, the file should contain ini‐
1019       tialization code (which will be executed then discarded) in addition to
1020       a  complete  function definition (which will be retained for subsequent
1021       calls to the function), and a call to the shell function, including any
1022       arguments, at the end.
1023
1024       For example, suppose the autoload file func contains
1025
1026              func() { print This is func; }
1027              print func is initialized
1028
1029       then  `func;  func' with KSH_AUTOLOAD set will produce both messages on
1030       the first call, but only the message `This is func' on the  second  and
1031       subsequent  calls.   Without KSH_AUTOLOAD set, it will produce the ini‐
1032       tialization message on the first call, and the  other  message  on  the
1033       second and subsequent calls.
1034
1035       It  is  also  possible  to  create  a  function  that  is not marked as
1036       autoloaded, but which loads its own definition by searching  fpath,  by
1037       using  `autoload -X' within a shell function.  For example, the follow‐
1038       ing are equivalent:
1039
1040              myfunc() {
1041                autoload -X
1042              }
1043              myfunc args...
1044
1045       and
1046
1047              unfunction myfunc   # if myfunc was defined
1048              autoload myfunc
1049              myfunc args...
1050
1051       In fact, the functions command outputs `builtin  autoload  -X'  as  the
1052       body of an autoloaded function.  This is done so that
1053
1054              eval "$(functions)"
1055
1056       produces  a reasonable result.  A true autoloaded function can be iden‐
1057       tified by the presence of  the  comment  `#  undefined'  in  the  body,
1058       because all comments are discarded from defined functions.
1059
1060       To load the definition of an autoloaded function myfunc without execut‐
1061       ing myfunc, use:
1062
1063              autoload +X myfunc
1064

ANONYMOUS FUNCTIONS

1066       If no name is given for a function, it is `anonymous'  and  is  handled
1067       specially.  Either form of function definition may be used: a `()' with
1068       no preceding name, or a `function' with an immediately  following  open
1069       brace.  The function is executed immediately at the point of definition
1070       and is not stored  for  future  use.   The  function  name  is  set  to
1071       `(anon)'.
1072
1073       Arguments to the function may be specified as words following the clos‐
1074       ing brace defining the function, hence if there are none  no  arguments
1075       (other than $0) are set.  This is a difference from the way other func‐
1076       tions are parsed: normal function definitions may be followed  by  cer‐
1077       tain  keywords  such  as `else' or `fi', which will be treated as argu‐
1078       ments to anonymous functions, so that a newline or semicolon is  needed
1079       to force keyword interpretation.
1080
1081       Note also that the argument list of any enclosing script or function is
1082       hidden (as would be the case for any  other  function  called  at  this
1083       point).
1084
1085       Redirections  may be applied to the anonymous function in the same man‐
1086       ner as to a current-shell structure enclosed in braces.  The  main  use
1087       of anonymous functions is to provide a scope for local variables.  This
1088       is particularly convenient in start-up files as these  do  not  provide
1089       their own local variable scope.
1090
1091       For example,
1092
1093              variable=outside
1094              function {
1095                local variable=inside
1096                print "I am $variable with arguments $*"
1097              } this and that
1098              print "I am $variable"
1099
1100       outputs the following:
1101
1102              I am inside with arguments this and that
1103              I am outside
1104
1105       Note  that  function definitions with arguments that expand to nothing,
1106       for example `name=; function $name { ... }', are not treated as  anony‐
1107       mous  functions.   Instead, they are treated as normal function defini‐
1108       tions where the definition is silently discarded.
1109

SPECIAL FUNCTIONS

1111       Certain functions, if defined, have special meaning to the shell.
1112
1113   Hook Functions
1114       For the functions below, it is possible to define an array that has the
1115       same  name  as the function with `_functions' appended.  Any element in
1116       such an array is taken as the name of a function to execute; it is exe‐
1117       cuted  in  the  same  context  and with the same arguments as the basic
1118       function.  For example, if $chpwd_functions is an array containing  the
1119       values  `mychpwd',  `chpwd_save_dirstack',  then  the shell attempts to
1120       execute the functions `chpwd', `mychpwd' and `chpwd_save_dirstack',  in
1121       that  order.   Any function that does not exist is silently ignored.  A
1122       function found by this mechanism is referred to elsewhere  as  a  `hook
1123       function'.  An error in any function causes subsequent functions not to
1124       be run.  Note further that an error in a precmd hook causes an  immedi‐
1125       ately  following periodic function not to run (though it may run at the
1126       next opportunity).
1127
1128       chpwd  Executed whenever the current working directory is changed.
1129
1130       periodic
1131              If the parameter PERIOD is set, this function is executed  every
1132              $PERIOD  seconds,  just  before a prompt.  Note that if multiple
1133              functions are defined using the  array  periodic_functions  only
1134              one  period is applied to the complete set of functions, and the
1135              scheduled time is not reset if the list of functions is altered.
1136              Hence the set of functions is always called together.
1137
1138       precmd Executed before each prompt.  Note that precommand functions are
1139              not re-executed simply because the command line is  redrawn,  as
1140              happens,  for  example, when a notification about an exiting job
1141              is displayed.
1142
1143       preexec
1144              Executed just after a command has been read and is about  to  be
1145              executed.   If  the  history  mechanism is active (regardless of
1146              whether the line was discarded from  the  history  buffer),  the
1147              string that the user typed is passed as the first argument, oth‐
1148              erwise it is an empty string.  The actual command that  will  be
1149              executed (including expanded aliases) is passed in two different
1150              forms: the second argument is a single-line,  size-limited  ver‐
1151              sion  of  the command (with things like function bodies elided);
1152              the third argument contains the full text  that  is  being  exe‐
1153              cuted.
1154
1155       zshaddhistory
1156              Executed  when  a  history line has been read interactively, but
1157              before it is executed.  The sole argument is the  complete  his‐
1158              tory  line  (so  that  any  terminating  newline  will  still be
1159              present).
1160
1161              If any of the hook functions returns status 1 (or  any  non-zero
1162              value  other  than  2,  though this is not guaranteed for future
1163              versions of the shell) the  history  line  will  not  be  saved,
1164              although  it  lingers in the history until the next line is exe‐
1165              cuted, allowing you to reuse or edit it immediately.
1166
1167              If any of the hook functions returns status 2 the  history  line
1168              will  be  saved on the internal history list, but not written to
1169              the history file.  In case of a  conflict,  the  first  non-zero
1170              status value is taken.
1171
1172              A  hook function may call `fc -p ...' to switch the history con‐
1173              text so that the history is saved in a different file  from  the
1174              that  in  the  global  HISTFILE parameter.  This is handled spe‐
1175              cially: the history context is automatically restored after  the
1176              processing of the history line is finished.
1177
1178              The  following  example  function  works with one of the options
1179              INC_APPEND_HISTORY or SHARE_HISTORY set, in order that the  line
1180              is written out immediately after the history entry is added.  It
1181              first adds the history line to the normal history with the  new‐
1182              line  stripped, which is usually the correct behaviour.  Then it
1183              switches the history context so that the line will be written to
1184              a history file in the current directory.
1185
1186                     zshaddhistory() {
1187                       print -sr -- ${1%%$'\n'}
1188                       fc -p .zsh_local_history
1189                     }
1190
1191       zshexit
1192              Executed at the point where the main shell is about to exit nor‐
1193              mally.  This is not called by exiting subshells,  nor  when  the
1194              exec  precommand  modifier  is  used before an external command.
1195              Also, unlike TRAPEXIT, it is not called when functions exit.
1196
1197   Trap Functions
1198       The functions below are treated specially but do not have corresponding
1199       hook arrays.
1200
1201       TRAPNAL
1202              If defined and non-null, this function will be executed whenever
1203              the shell catches a signal SIGNAL, where NAL is a signal name as
1204              specified  for  the  kill  builtin.   The  signal number will be
1205              passed as the first parameter to the function.
1206
1207              If a function of this form is defined and null,  the  shell  and
1208              processes spawned by it will ignore SIGNAL.
1209
1210              The return status from the function is handled specially.  If it
1211              is zero, the signal is assumed to have been handled, and  execu‐
1212              tion  continues  normally.   Otherwise, the shell will behave as
1213              interrupted except  that  the  return  status  of  the  trap  is
1214              retained.
1215
1216              Programs  terminated  by  uncaught  signals typically return the
1217              status 128 plus the signal number.  Hence the  following  causes
1218              the  handler for SIGINT to print a message, then mimic the usual
1219              effect of the signal.
1220
1221                     TRAPINT() {
1222                       print "Caught SIGINT, aborting."
1223                       return $(( 128 + $1 ))
1224                     }
1225
1226              The functions TRAPZERR, TRAPDEBUG and TRAPEXIT  are  never  exe‐
1227              cuted inside other traps.
1228
1229       TRAPDEBUG
1230              If  the  option  DEBUG_BEFORE_CMD  is set (as it is by default),
1231              executed before each command; otherwise executed after each com‐
1232              mand.  See the description of the trap builtin in zshbuiltins(1)
1233              for details of additional features provided in debug traps.
1234
1235       TRAPEXIT
1236              Executed when the shell exits,  or  when  the  current  function
1237              exits  if  defined  inside  a  function.  The value of $? at the
1238              start of execution is the exit status of the shell or the return
1239              status of the function exiting.
1240
1241       TRAPZERR
1242              Executed  whenever  a  command has a non-zero exit status.  How‐
1243              ever, the function is not executed if the command occurred in  a
1244              sublist  followed  by  `&&' or `||'; only the final command in a
1245              sublist of this type causes the trap to be executed.  The  func‐
1246              tion TRAPERR acts the same as TRAPZERR on systems where there is
1247              no SIGERR (this is the usual case).
1248
1249       The functions beginning `TRAP' may alternatively be  defined  with  the
1250       trap  builtin:   this  may be preferable for some uses.  Setting a trap
1251       with one form removes any trap of the other form for the  same  signal;
1252       removing  a  trap in either form removes all traps for the same signal.
1253       The forms
1254
1255              TRAPNAL() {
1256               # code
1257              }
1258
1259       ('function traps') and
1260
1261              trap '
1262               # code
1263              ' NAL
1264
1265       ('list traps') are equivalent in most ways, the  exceptions  being  the
1266       following:
1267
1268       ·      Function  traps  have  all  the  properties of normal functions,
1269              appearing in the list of functions and being called  with  their
1270              own  function context rather than the context where the trap was
1271              triggered.
1272
1273       ·      The return status from function  traps  is  special,  whereas  a
1274              return from a list trap causes the surrounding context to return
1275              with the given status.
1276
1277       ·      Function traps are not reset  within  subshells,  in  accordance
1278              with  zsh  behaviour;  list  traps are reset, in accordance with
1279              POSIX behaviour.
1280

JOBS

1282       If the MONITOR option is set, an interactive  shell  associates  a  job
1283       with  each  pipeline.  It keeps a table of current jobs, printed by the
1284       jobs command, and assigns them small integer numbers.  When  a  job  is
1285       started  asynchronously  with  `&', the shell prints a line to standard
1286       error which looks like:
1287
1288              [1] 1234
1289
1290       indicating that the job which was started asynchronously was job number
1291       1 and had one (top-level) process, whose process ID was 1234.
1292
1293       If  a  job  is  started with `&|' or `&!', then that job is immediately
1294       disowned.  After startup, it does not have a place in  the  job  table,
1295       and is not subject to the job control features described here.
1296
1297       If  you are running a job and wish to do something else you may hit the
1298       key ^Z (control-Z) which sends a TSTP signal to the current job:   this
1299       key  may  be redefined by the susp option of the external stty command.
1300       The shell will then normally indicate  that  the  job  has  been  `sus‐
1301       pended',  and  print another prompt.  You can then manipulate the state
1302       of this job, putting it in the background with the bg command,  or  run
1303       some  other  commands  and  then eventually bring the job back into the
1304       foreground with the foreground command fg.  A ^Z takes  effect  immedi‐
1305       ately  and is like an interrupt in that pending output and unread input
1306       are discarded when it is typed.
1307
1308       A job being run in the background will suspend if it tries to read from
1309       the terminal.
1310
1311       Note  that  if  the  job running in the foreground is a shell function,
1312       then suspending it will have the effect of causing the shell  to  fork.
1313       This  is  necessary  to  separate the function's state from that of the
1314       parent shell performing the job control, so that the latter can  return
1315       to  the  command  line prompt.  As a result, even if fg is used to con‐
1316       tinue the job the function will no longer be part of the parent  shell,
1317       and any variables set by the function will not be visible in the parent
1318       shell.  Thus the behaviour is different from the case where  the  func‐
1319       tion  was  never suspended.  Zsh is different from many other shells in
1320       this regard.
1321
1322       One additional side effect is that use of disown with a job created  by
1323       suspending  shell  code in this fashion is delayed: the job can only be
1324       disowned once any process started from the parent shell has terminated.
1325       At that point, the disowned job disappears silently from the job list.
1326
1327       The  same  behaviour  is  found when the shell is executing code as the
1328       right hand side of a pipeline or any complex shell  construct  such  as
1329       if, for, etc., in order that the entire block of code can be managed as
1330       a single job.  Background jobs are normally allowed to produce  output,
1331       but  this  can be disabled by giving the command `stty tostop'.  If you
1332       set this tty option, then background jobs will suspend when they try to
1333       produce output like they do when they try to read input.
1334
1335       When  a  command  is  suspended and continued later with the fg or wait
1336       builtins, zsh restores tty modes that were in effect when it  was  sus‐
1337       pended.   This (intentionally) does not apply if the command is contin‐
1338       ued via `kill -CONT', nor when it is continued with bg.
1339
1340       There are several ways to refer to jobs in the shell.   A  job  can  be
1341       referred  to  by  the process ID of any process of the job or by one of
1342       the following:
1343
1344       %number
1345              The job with the given number.
1346       %string
1347              The last job whose command line begins with string.
1348       %?string
1349              The last job whose command line contains string.
1350       %%     Current job.
1351       %+     Equivalent to `%%'.
1352       %-     Previous job.
1353
1354       The shell learns immediately whenever a process changes state.  It nor‐
1355       mally  informs  you  whenever  a job becomes blocked so that no further
1356       progress is possible.  If the NOTIFY option is not set, it waits  until
1357       just before it prints a prompt before it informs you.  All such notifi‐
1358       cations are sent directly to the terminal, not to the  standard  output
1359       or standard error.
1360
1361       When  the  monitor mode is on, each background job that completes trig‐
1362       gers any trap set for CHLD.
1363
1364       When you try to leave the shell while jobs are  running  or  suspended,
1365       you  will  be warned that `You have suspended (running) jobs'.  You may
1366       use the jobs command to see what they are.  If you do this  or  immedi‐
1367       ately try to exit again, the shell will not warn you a second time; the
1368       suspended jobs will be terminated, and the running jobs will be sent  a
1369       SIGHUP signal, if the HUP option is set.
1370
1371       To  avoid  having  the shell terminate the running jobs, either use the
1372       nohup command (see nohup(1)) or the disown builtin.
1373

SIGNALS

1375       The INT and QUIT signals for an invoked command are ignored if the com‐
1376       mand  is  followed  by  `&'  and the MONITOR option is not active.  The
1377       shell itself always ignores the QUIT signal.  Otherwise,  signals  have
1378       the  values inherited by the shell from its parent (but see the TRAPNAL
1379       special functions in the section `Functions').
1380
1381       Certain jobs are run asynchronously  by  the  shell  other  than  those
1382       explicitly put into the background; even in cases where the shell would
1383       usually wait for such jobs, an explicit exit command or exit due to the
1384       option ERR_EXIT will cause the shell to exit without waiting.  Examples
1385       of such asynchronous jobs are process  substitution,  see  the  section
1386       PROCESS  SUBSTITUTION  in  the  zshexpn(1) manual page, and the handler
1387       processes for multios, see the section MULTIOS in the zshmisc(1) manual
1388       page.
1389

ARITHMETIC EVALUATION

1391       The  shell  can  perform  integer and floating point arithmetic, either
1392       using the builtin let, or via a substitution of the form $((...)).  For
1393       integers,  the  shell is usually compiled to use 8-byte precision where
1394       this is available, otherwise precision is 4 bytes.  This can be tested,
1395       for example, by giving the command `print - $(( 12345678901 ))'; if the
1396       number appears unchanged, the precision is at least 8 bytes.   Floating
1397       point  arithmetic  always  uses  the `double' type with whatever corre‐
1398       sponding precision is provided by the compiler and the library.
1399
1400       The let builtin command takes arithmetic expressions as arguments; each
1401       is  evaluated  separately.   Since many of the arithmetic operators, as
1402       well as spaces, require quoting, an alternative form is  provided:  for
1403       any command which begins with a `((', all the characters until a match‐
1404       ing `))' are treated as a quoted expression  and  arithmetic  expansion
1405       performed  as  for  an  argument  of let.  More precisely, `((...))' is
1406       equivalent to `let "..."'.  The return status is 0  if  the  arithmetic
1407       value of the expression is non-zero, 1 if it is zero, and 2 if an error
1408       occurred.
1409
1410       For example, the following statement
1411
1412              (( val = 2 + 1 ))
1413
1414       is equivalent to
1415
1416              let "val = 2 + 1"
1417
1418       both assigning the value 3 to the shell variable val  and  returning  a
1419       zero status.
1420
1421       Integers can be in bases other than 10.  A leading `0x' or `0X' denotes
1422       hexadecimal and a leading `0b' or `0B' binary.  Integers may also be of
1423       the  form  `base#n',  where  base  is  a decimal number between two and
1424       thirty-six representing the arithmetic base and n is a number  in  that
1425       base  (for example, `16#ff' is 255 in hexadecimal).  The base# may also
1426       be omitted, in which case base 10 is used.  For backwards compatibility
1427       the form `[base]n' is also accepted.
1428
1429       An  integer expression or a base given in the form `base#n' may contain
1430       underscores (`_') after the leading digit for  visual  guidance;  these
1431       are  ignored  in  computation.   Examples  are 1_000_000 or 0xffff_ffff
1432       which are equivalent to 1000000 and 0xffffffff respectively.
1433
1434       It is also possible to specify a base to be used for output in the form
1435       `[#base]',  for  example  `[#16]'.  This is used when outputting arith‐
1436       metical substitutions or when assigning to scalar  parameters,  but  an
1437       explicitly  defined  integer  or  floating  point parameter will not be
1438       affected.  If an integer variable is implicitly defined  by  an  arith‐
1439       metic  expression,  any  base  specified in this way will be set as the
1440       variable's output arithmetic base as if the option  `-i  base'  to  the
1441       typeset builtin had been used.  The expression has no precedence and if
1442       it occurs more than once in a mathematical expression, the last encoun‐
1443       tered  is  used.   For  clarity it is recommended that it appear at the
1444       beginning of an expression.  As an example:
1445
1446              typeset -i 16 y
1447              print $(( [#8] x = 32, y = 32 ))
1448              print $x $y
1449
1450       outputs first `8#40', the rightmost value in the given output base, and
1451       then  `8#40 16#20', because y has been explicitly declared to have out‐
1452       put base 16, while x (assuming it does not already exist) is implicitly
1453       typed  by  the arithmetic evaluation, where it acquires the output base
1454       8.
1455
1456       The base may be replaced or followed by an underscore, which may itself
1457       be  followed  by  a  positive  integer (if it is missing the value 3 is
1458       used).  This indicates that underscores should  be  inserted  into  the
1459       output  string,  grouping the number for visual clarity.  The following
1460       integer specifies the number of digits to group together.  For example:
1461
1462              setopt cbases
1463              print $(( [#16_4] 65536 ** 2 ))
1464
1465       outputs `0x1_0000_0000'.
1466
1467       The feature can be used with floating point numbers, in which case  the
1468       base  must  be  omitted;  grouping is away from the decimal point.  For
1469       example,
1470
1471              zmodload zsh/mathfunc
1472              print $(( [#_] sqrt(1e7) ))
1473
1474       outputs `3_162.277_660_168_379_5' (the number of decimal  places  shown
1475       may vary).
1476
1477       If  the  C_BASES  option  is set, hexadecimal numbers are output in the
1478       standard C format, for example `0xFF' instead of the usual `16#FF'.  If
1479       the  option OCTAL_ZEROES is also set (it is not by default), octal num‐
1480       bers will be treated similarly and hence appear  as  `077'  instead  of
1481       `8#77'.   This  option  has no effect on the output of bases other than
1482       hexadecimal and octal, and  these  formats  are  always  understood  on
1483       input.
1484
1485       When  an output base is specified using the `[#base]' syntax, an appro‐
1486       priate base prefix will be output if necessary, so that the value  out‐
1487       put  is  valid  syntax  for  input.   If  the # is doubled, for example
1488       `[##16]', then no base prefix is output.
1489
1490       Floating point constants are recognized by the presence  of  a  decimal
1491       point  or an exponent.  The decimal point may be the first character of
1492       the constant, but the exponent character e or E may not, as it will  be
1493       taken  for  a  parameter name.  All numeric parts (before and after the
1494       decimal point and in the exponent) may contain  underscores  after  the
1495       leading digit for visual guidance; these are ignored in computation.
1496
1497       An  arithmetic expression uses nearly the same syntax and associativity
1498       of expressions as in C.
1499
1500       In the native mode of operation, the following operators are  supported
1501       (listed in decreasing order of precedence):
1502
1503       + - ! ~ ++ --
1504              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1505              ment
1506       << >>  bitwise shift left, right
1507       &      bitwise AND
1508       ^      bitwise XOR
1509       |      bitwise OR
1510       **     exponentiation
1511       * / %  multiplication, division, modulus (remainder)
1512       + -    addition, subtraction
1513       < > <= >=
1514              comparison
1515       == !=  equality and inequality
1516       &&     logical AND
1517       || ^^  logical OR, XOR
1518       ? :    ternary operator
1519       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1520              assignment
1521       ,      comma operator
1522
1523       The operators `&&', `||', `&&=', and `||='  are  short-circuiting,  and
1524       only  one of the latter two expressions in a ternary operator is evalu‐
1525       ated.  Note the precedence of the bitwise AND, OR, and XOR operators.
1526
1527       With the option C_PRECEDENCES the precedences (but no other properties)
1528       of the operators are altered to be the same as those in most other lan‐
1529       guages that support the relevant operators:
1530
1531       + - ! ~ ++ --
1532              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1533              ment
1534       **     exponentiation
1535       * / %  multiplication, division, modulus (remainder)
1536       + -    addition, subtraction
1537       << >>  bitwise shift left, right
1538       < > <= >=
1539              comparison
1540       == !=  equality and inequality
1541       &      bitwise AND
1542       ^      bitwise XOR
1543       |      bitwise OR
1544       &&     logical AND
1545       ^^     logical XOR
1546       ||     logical OR
1547       ? :    ternary operator
1548       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1549              assignment
1550       ,      comma operator
1551
1552       Note  the  precedence  of exponentiation in both cases is below that of
1553       unary operators, hence `-3**2' evaluates as `9', not `-9'.  Use  paren‐
1554       theses  where  necessary:  `-(3**2)'.   This  is for compatibility with
1555       other shells.
1556
1557       Mathematical functions can be  called  with  the  syntax  `func(args)',
1558       where  the  function  decides  if  the  args  is  used as a string or a
1559       comma-separated list of arithmetic  expressions.  The  shell  currently
1560       defines  no mathematical functions by default, but the module zsh/math‐
1561       func may be loaded with the zmodload builtin to provide standard float‐
1562       ing point mathematical functions.
1563
1564       An  expression of the form `##x' where x is any character sequence such
1565       as `a', `^A', or `\M-\C-x' gives the value of  this  character  and  an
1566       expression  of  the form `#name' gives the value of the first character
1567       of the contents of the parameter name.  Character values are  according
1568       to  the character set used in the current locale; for multibyte charac‐
1569       ter handling the option MULTIBYTE must be set.  Note that this form  is
1570       different  from `$#name', a standard parameter substitution which gives
1571       the length of the parameter name.  `#\' is accepted  instead  of  `##',
1572       but its use is deprecated.
1573
1574       Named  parameters  and  subscripted  arrays  can  be referenced by name
1575       within an arithmetic expression without using the  parameter  expansion
1576       syntax.  For example,
1577
1578              ((val2 = val1 * 2))
1579
1580       assigns twice the value of $val1 to the parameter named val2.
1581
1582       An  internal  integer representation of a named parameter can be speci‐
1583       fied with the integer builtin.  Arithmetic evaluation is  performed  on
1584       the  value  of each assignment to a named parameter declared integer in
1585       this manner.  Assigning a floating point number to an  integer  results
1586       in rounding towards zero.
1587
1588       Likewise,  floating  point  numbers  can  be  declared  with  the float
1589       builtin; there are two types, differing only in their output format, as
1590       described  for  the typeset builtin.  The output format can be bypassed
1591       by using arithmetic substitution instead of the parameter substitution,
1592       i.e.  `${float}'  uses  the  defined  format,  but  `$((float))' uses a
1593       generic floating point format.
1594
1595       Promotion of integer to floating point values is performed where neces‐
1596       sary.   In  addition,  if  any operator which requires an integer (`&',
1597       `|', `^', `<<', `>>' and their equivalents with assignment) is given  a
1598       floating  point  argument,  it  will  be  silently rounded towards zero
1599       except for `~' which rounds down.
1600
1601       Users should beware that, in common with many  other  programming  lan‐
1602       guages  but not software designed for calculation, the evaluation of an
1603       expression in zsh is taken a term at a time and promotion  of  integers
1604       to  floating point does not occur in terms only containing integers.  A
1605       typical result of this is that a division such as 6/8 is truncated,  in
1606       this being rounded towards 0.  The FORCE_FLOAT shell option can be used
1607       in scripts or functions where floating  point  evaluation  is  required
1608       throughout.
1609
1610       Scalar variables can hold integer or floating point values at different
1611       times; there is no memory of the numeric type in this case.
1612
1613       If a variable is first assigned in a numeric context without previously
1614       being  declared,  it  will  be implicitly typed as integer or float and
1615       retain that type either until the type is explicitly changed  or  until
1616       the  end  of  the  scope.   This can have unforeseen consequences.  For
1617       example, in the loop
1618
1619              for (( f = 0; f < 1; f += 0.1 )); do
1620              # use $f
1621              done
1622
1623       if f has not already been declared, the first assignment will cause  it
1624       to  be created as an integer, and consequently the operation `f += 0.1'
1625       will always cause the result to be truncated to zero, so that the  loop
1626       will  fail.  A simple fix would be to turn the initialization into `f =
1627       0.0'.  It is therefore best to declare numeric variables with  explicit
1628       types.
1629

CONDITIONAL EXPRESSIONS

1631       A  conditional  expression is used with the [[ compound command to test
1632       attributes of files and to compare strings.   Each  expression  can  be
1633       constructed  from  one or more of the following unary or binary expres‐
1634       sions:
1635
1636       -a file
1637              true if file exists.
1638
1639       -b file
1640              true if file exists and is a block special file.
1641
1642       -c file
1643              true if file exists and is a character special file.
1644
1645       -d file
1646              true if file exists and is a directory.
1647
1648       -e file
1649              true if file exists.
1650
1651       -f file
1652              true if file exists and is a regular file.
1653
1654       -g file
1655              true if file exists and has its setgid bit set.
1656
1657       -h file
1658              true if file exists and is a symbolic link.
1659
1660       -k file
1661              true if file exists and has its sticky bit set.
1662
1663       -n string
1664              true if length of string is non-zero.
1665
1666       -o option
1667              true if option named option is on.  option may be a single char‐
1668              acter,  in  which  case it is a single letter option name.  (See
1669              the section `Specifying Options'.)
1670
1671              When no option  named  option  exists,  and  the  POSIX_BUILTINS
1672              option hasn't been set, return 3 with a warning.  If that option
1673              is set, return 1 with no warning.
1674
1675       -p file
1676              true if file exists and is a FIFO special file (named pipe).
1677
1678       -r file
1679              true if file exists and is readable by current process.
1680
1681       -s file
1682              true if file exists and has size greater than zero.
1683
1684       -t fd  true if file descriptor number fd is open and associated with  a
1685              terminal device.  (note: fd is not optional)
1686
1687       -u file
1688              true if file exists and has its setuid bit set.
1689
1690       -v varname
1691              true if shell variable varname is set.
1692
1693       -w file
1694              true if file exists and is writable by current process.
1695
1696       -x file
1697              true  if  file  exists and is executable by current process.  If
1698              file exists and is a directory, then  the  current  process  has
1699              permission to search in the directory.
1700
1701       -z string
1702              true if length of string is zero.
1703
1704       -L file
1705              true if file exists and is a symbolic link.
1706
1707       -O file
1708              true  if  file  exists  and is owned by the effective user ID of
1709              this process.
1710
1711       -G file
1712              true if file exists and its group matches the effective group ID
1713              of this process.
1714
1715       -S file
1716              true if file exists and is a socket.
1717
1718       -N file
1719              true  if  file  exists and its access time is not newer than its
1720              modification time.
1721
1722       file1 -nt file2
1723              true if file1 exists and is newer than file2.
1724
1725       file1 -ot file2
1726              true if file1 exists and is older than file2.
1727
1728       file1 -ef file2
1729              true if file1 and file2 exist and refer to the same file.
1730
1731       string = pattern
1732       string == pattern
1733              true if string matches  pattern.   The  two  forms  are  exactly
1734              equivalent.   The  `=' form is the traditional shell syntax (and
1735              hence the only one generally used with the test and [ builtins);
1736              the  `=='  form  provides compatibility with other sorts of com‐
1737              puter language.
1738
1739       string != pattern
1740              true if string does not match pattern.
1741
1742       string =~ regexp
1743              true if string matches the regular expression  regexp.   If  the
1744              option  RE_MATCH_PCRE  is set regexp is tested as a PCRE regular
1745              expression using the zsh/pcre module, else it  is  tested  as  a
1746              POSIX  extended  regular  expression using the zsh/regex module.
1747              Upon successful match, some variables will be updated; no  vari‐
1748              ables are changed if the matching fails.
1749
1750              If the option BASH_REMATCH is not set the scalar parameter MATCH
1751              is set to the substring that matched the pattern and the integer
1752              parameters  MBEGIN  and  MEND to the index of the start and end,
1753              respectively, of the match in string, such  that  if  string  is
1754              contained in variable var the expression `${var[$MBEGIN,$MEND]}'
1755              is identical to `$MATCH'.  The setting of the option  KSH_ARRAYS
1756              is  respected.   Likewise,  the  array  match is set to the sub‐
1757              strings that matched parenthesised subexpressions and the arrays
1758              mbegin  and  mend to the indices of the start and end positions,
1759              respectively, of the substrings within string.  The  arrays  are
1760              not  set  if  there  were no parenthesised subexpresssions.  For
1761              example, if the string `a short string' is matched  against  the
1762              regular   expression   `s(...)t',   then  (assuming  the  option
1763              KSH_ARRAYS is not set) MATCH, MBEGIN and MEND are `short', 3 and
1764              7,  respectively,  while match, mbegin and mend are single entry
1765              arrays containing the strings `hor', `4' and `6', respectively.
1766
1767              If the option BASH_REMATCH is set the array BASH_REMATCH is  set
1768              to  the  substring that matched the pattern followed by the sub‐
1769              strings that matched  parenthesised  subexpressions  within  the
1770              pattern.
1771
1772       string1 < string2
1773              true  if  string1  comes  before string2 based on ASCII value of
1774              their characters.
1775
1776       string1 > string2
1777              true if string1 comes after string2  based  on  ASCII  value  of
1778              their characters.
1779
1780       exp1 -eq exp2
1781              true if exp1 is numerically equal to exp2.  Note that for purely
1782              numeric comparisons use of the ((...)) builtin described in  the
1783              section  `ARITHMETIC  EVALUATION' is more convenient than condi‐
1784              tional expressions.
1785
1786       exp1 -ne exp2
1787              true if exp1 is numerically not equal to exp2.
1788
1789       exp1 -lt exp2
1790              true if exp1 is numerically less than exp2.
1791
1792       exp1 -gt exp2
1793              true if exp1 is numerically greater than exp2.
1794
1795       exp1 -le exp2
1796              true if exp1 is numerically less than or equal to exp2.
1797
1798       exp1 -ge exp2
1799              true if exp1 is numerically greater than or equal to exp2.
1800
1801       ( exp )
1802              true if exp is true.
1803
1804       ! exp  true if exp is false.
1805
1806       exp1 && exp2
1807              true if exp1 and exp2 are both true.
1808
1809       exp1 || exp2
1810              true if either exp1 or exp2 is true.
1811
1812       For compatibility, if there is a single argument that is not  syntacti‐
1813       cally  significant, typically a variable, the condition is treated as a
1814       test for whether the expression expands as a string of non-zero length.
1815       In  other words, [[ $var ]] is the same as [[ -n $var ]].  It is recom‐
1816       mended that the second, explicit, form be used where possible.
1817
1818       Normal shell expansion is performed on the  file,  string  and  pattern
1819       arguments, but the result of each expansion is constrained to be a sin‐
1820       gle word, similar to the effect of double quotes.
1821
1822       Filename generation is not performed on any form of argument to  condi‐
1823       tions.  However, it can be forced in any case where normal shell expan‐
1824       sion is valid and when the option EXTENDED_GLOB is in effect  by  using
1825       an  explicit  glob qualifier of the form (#q) at the end of the string.
1826       A normal glob qualifier expression may appear between the `q'  and  the
1827       closing  parenthesis;  if  none  appears  the  expression has no effect
1828       beyond causing filename generation.  The results of filename generation
1829       are joined together to form a single word, as with the results of other
1830       forms of expansion.
1831
1832       This special use of filename generation is only available with  the  [[
1833       syntax.   If the condition occurs within the [ or test builtin commands
1834       then globbing occurs instead as part of normal command  line  expansion
1835       before the condition is evaluated.  In this case it may generate multi‐
1836       ple words which are likely to confuse the syntax of the test command.
1837
1838       For example,
1839
1840              [[ -n file*(#qN) ]]
1841
1842       produces status zero if and only if there is at least one file  in  the
1843       current directory beginning with the string `file'.  The globbing qual‐
1844       ifier N ensures that the expression is empty if there  is  no  matching
1845       file.
1846
1847       Pattern  metacharacters  are active for the pattern arguments; the pat‐
1848       terns are the same as those used  for  filename  generation,  see  zsh‐
1849       expn(1), but there is no special behaviour of `/' nor initial dots, and
1850       no glob qualifiers are allowed.
1851
1852       In each of the above expressions, if file is of the  form  `/dev/fd/n',
1853       where  n  is  an  integer, then the test applied to the open file whose
1854       descriptor number is n, even if the underlying system does not  support
1855       the /dev/fd directory.
1856
1857       In  the  forms which do numeric comparison, the expressions exp undergo
1858       arithmetic expansion as if they were enclosed in $((...)).
1859
1860       For example, the following:
1861
1862              [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
1863
1864       tests if either file foo or file bar exists, and if so, if the value of
1865       the  parameter  report  begins  with  `y'; if the complete condition is
1866       true, the message `File exists.' is printed.
1867

EXPANSION OF PROMPT SEQUENCES

1869       Prompt sequences undergo a special form of  expansion.   This  type  of
1870       expansion is also available using the -P option to the print builtin.
1871
1872       If the PROMPT_SUBST option is set, the prompt string is first subjected
1873       to parameter expansion, command substitution and arithmetic  expansion.
1874       See zshexpn(1).
1875
1876       Certain escape sequences may be recognised in the prompt string.
1877
1878       If  the  PROMPT_BANG  option is set, a `!' in the prompt is replaced by
1879       the current history event number.  A literal `!'  may  then  be  repre‐
1880       sented as `!!'.
1881
1882       If  the  PROMPT_PERCENT  option  is  set, certain escape sequences that
1883       start with `%' are expanded.  Many escapes are  followed  by  a  single
1884       character,  although  some  of  these take an optional integer argument
1885       that should appear between the  `%'  and  the  next  character  of  the
1886       sequence.   More  complicated escape sequences are available to provide
1887       conditional expansion.
1888

SIMPLE PROMPT ESCAPES

1890   Special characters
1891       %%     A `%'.
1892
1893       %)     A `)'.
1894
1895   Login information
1896       %l     The line (tty) the user is logged in on, without `/dev/' prefix.
1897              If the name starts with `/dev/tty', that prefix is stripped.
1898
1899       %M     The full machine hostname.
1900
1901       %m     The hostname up to the first `.'.  An integer may follow the `%'
1902              to specify how many components  of  the  hostname  are  desired.
1903              With a negative integer, trailing components of the hostname are
1904              shown.
1905
1906       %n     $USERNAME.
1907
1908       %y     The line (tty) the user is logged in on, without `/dev/' prefix.
1909              This does not treat `/dev/tty' names specially.
1910
1911   Shell state
1912       %#     A  `#'  if  the  shell is running with privileges, a `%' if not.
1913              Equivalent to `%(!.#.%%)'.  The definition of `privileged',  for
1914              these  purposes,  is  that either the effective user ID is zero,
1915              or, if POSIX.1e capabilities are supported, that  at  least  one
1916              capability  is  raised  in  either  the Effective or Inheritable
1917              capability vectors.
1918
1919       %?     The return status of the last command executed just  before  the
1920              prompt.
1921
1922       %_     The  status  of the parser, i.e. the shell constructs (like `if'
1923              and `for') that have been started on the command line. If  given
1924              an  integer  number  that  many strings will be printed; zero or
1925              negative or no integer means print as many as there  are.   This
1926              is most useful in prompts PS2 for continuation lines and PS4 for
1927              debugging with the XTRACE option; in the  latter  case  it  will
1928              also work non-interactively.
1929
1930       %^     The  status  of  the parser in reverse. This is the same as `%_'
1931              other than the order of strings.  It is often used in RPS2.
1932
1933       %d
1934       %/     Current working directory.  If an integer follows  the  `%',  it
1935              specifies a number of trailing components of the current working
1936              directory to show; zero means the whole path.  A negative  inte‐
1937              ger  specifies leading components, i.e. %-1d specifies the first
1938              component.
1939
1940       %~     As %d and %/, but if the current working directory  starts  with
1941              $HOME,  that part is replaced by a `~'. Furthermore, if it has a
1942              named directory as its prefix, that part is replaced  by  a  `~'
1943              followed by the name of the directory, but only if the result is
1944              shorter than the full path; see Dynamic and Static named  direc‐
1945              tories in zshexpn(1).
1946
1947       %e     Evaluation depth of the current sourced file, shell function, or
1948              eval.  This is incremented or decremented every time  the  value
1949              of  %N  is  set  or  reverted to a previous value, respectively.
1950              This is most useful for debugging as part of $PS4.
1951
1952       %h
1953       %!     Current history event number.
1954
1955       %i     The line number currently being executed in the script,  sourced
1956              file,  or  shell  function given by %N.  This is most useful for
1957              debugging as part of $PS4.
1958
1959       %I     The line number currently being executed in the file  %x.   This
1960              is similar to %i, but the line number is always a line number in
1961              the file where the code was defined, even if the code is a shell
1962              function.
1963
1964       %j     The number of jobs.
1965
1966       %L     The current value of $SHLVL.
1967
1968       %N     The name of the script, sourced file, or shell function that zsh
1969              is currently executing, whichever was started most recently.  If
1970              there is none, this is equivalent to the parameter $0.  An inte‐
1971              ger may follow the `%' to specify a number of trailing path com‐
1972              ponents  to  show; zero means the full path.  A negative integer
1973              specifies leading components.
1974
1975       %x     The name of the file containing the source code currently  being
1976              executed.  This behaves as %N except that function and eval com‐
1977              mand names are not shown,  instead  the  file  where  they  were
1978              defined.
1979
1980       %c
1981       %.
1982       %C     Trailing component of the current working directory.  An integer
1983              may follow the `%' to get more than one component.  Unless  `%C'
1984              is used, tilde contraction is performed first.  These are depre‐
1985              cated as %c and %C are equivalent to %1~ and %1/,  respectively,
1986              while explicit positive integers have the same effect as for the
1987              latter two sequences.
1988
1989   Date and time
1990       %D     The date in yy-mm-dd format.
1991
1992       %T     Current time of day, in 24-hour format.
1993
1994       %t
1995       %@     Current time of day, in 12-hour, am/pm format.
1996
1997       %*     Current time of day in 24-hour format, with seconds.
1998
1999       %w     The date in day-dd format.
2000
2001       %W     The date in mm/dd/yy format.
2002
2003       %D{string}
2004              string is formatted using  the  strftime  function.   See  strf‐
2005              time(3)  for  more details.  Various zsh extensions provide num‐
2006              bers with no leading zero or space if the  number  is  a  single
2007              digit:
2008
2009              %f     a day of the month
2010              %K     the hour of the day on the 24-hour clock
2011              %L     the hour of the day on the 12-hour clock
2012
2013              In  addition, if the system supports the POSIX gettimeofday sys‐
2014              tem call, %. provides decimal fractions of a  second  since  the
2015              epoch  with leading zeroes.  By default three decimal places are
2016              provided, but a number of digits up to 6 may be given  following
2017              the  %;  hence  %6.  outputs microseconds.  A typical example of
2018              this is the format `%D{%H:%M:%S.%.}'.
2019
2020              The GNU extension that a `-' between the % and the format  char‐
2021              acter  causes  a leading zero or space to be stripped is handled
2022              directly by the shell for the format characters d, f, H,  k,  l,
2023              m,  M,  S and y; any other format characters are provided to the
2024              system's strftime(3) with any leading `-' present, so  the  han‐
2025              dling  is  system  dependent.  Further GNU (or other) extensions
2026              are also passed to strftime(3) and may work if the  system  sup‐
2027              ports them.
2028
2029   Visual effects
2030       %B (%b)
2031              Start (stop) boldface mode.
2032
2033       %E     Clear to end of line.
2034
2035       %U (%u)
2036              Start (stop) underline mode.
2037
2038       %S (%s)
2039              Start (stop) standout mode.
2040
2041       %F (%f)
2042              Start  (stop)  using a different foreground colour, if supported
2043              by the terminal.  The colour may be specified two  ways:  either
2044              as  a  numeric  argument,  as normal, or by a sequence in braces
2045              following the %F, for example %F{red}.  In the latter  case  the
2046              values  allowed  are  as  described  for  the  fg  zle_highlight
2047              attribute; see Character Highlighting in zshzle(1).  This  means
2048              that numeric colours are allowed in the second format also.
2049
2050       %K (%k)
2051              Start (stop) using a different bacKground colour.  The syntax is
2052              identical to that for %F and %f.
2053
2054       %{...%}
2055              Include a string as  a  literal  escape  sequence.   The  string
2056              within  the braces should not change the cursor position.  Brace
2057              pairs can nest.
2058
2059              A positive numeric argument between the % and the {  is  treated
2060              as described for %G below.
2061
2062       %G     Within  a  %{...%} sequence, include a `glitch': that is, assume
2063              that a single character width will be output.   This  is  useful
2064              when  outputting  characters  that otherwise cannot be correctly
2065              handled by the shell, such as the  alternate  character  set  on
2066              some  terminals.   The  characters  in  question can be included
2067              within a %{...%} sequence together with the  appropriate  number
2068              of  %G  sequences  to  indicate  the  correct width.  An integer
2069              between the `%' and `G' indicates a character width  other  than
2070              one.   Hence  %{seq%2G%} outputs seq and assumes it takes up the
2071              width of two standard characters.
2072
2073              Multiple uses of %G accumulate in the obvious fashion; the posi‐
2074              tion  of  the %G is unimportant.  Negative integers are not han‐
2075              dled.
2076
2077              Note that when prompt truncation is in use it  is  advisable  to
2078              divide  up  output  into  single  characters within each %{...%}
2079              group so that the correct truncation point can be found.
2080

CONDITIONAL SUBSTRINGS IN PROMPTS

2082       %v     The value of the first element of  the  psvar  array  parameter.
2083              Following  the  `%'  with  an  integer gives that element of the
2084              array.  Negative integers count from the end of the array.
2085
2086       %(x.true-text.false-text)
2087              Specifies a ternary expression.  The character following  the  x
2088              is  arbitrary;  the  same character is used to separate the text
2089              for the `true' result from that for the  `false'  result.   This
2090              separator  may  not appear in the true-text, except as part of a
2091              %-escape sequence.  A `)' may appear in the false-text as  `%)'.
2092              true-text  and  false-text  may  both contain arbitrarily-nested
2093              escape sequences, including further ternary expressions.
2094
2095              The left parenthesis may be preceded or followed by  a  positive
2096              integer  n,  which defaults to zero.  A negative integer will be
2097              multiplied by -1, except as noted below for `l'.  The test char‐
2098              acter x may be any of the following:
2099
2100              !      True if the shell is running with privileges.
2101              #      True if the effective uid of the current process is n.
2102              ?      True if the exit status of the last command was n.
2103              _      True if at least n shell constructs were started.
2104              C
2105              /      True if the current absolute path has at least n elements
2106                     relative to the root directory, hence / is counted  as  0
2107                     elements.
2108              c
2109              .
2110              ~      True if the current path, with prefix replacement, has at
2111                     least n elements relative to the root directory, hence  /
2112                     is counted as 0 elements.
2113              D      True if the month is equal to n (January = 0).
2114              d      True if the day of the month is equal to n.
2115              e      True if the evaluation depth is at least n.
2116              g      True if the effective gid of the current process is n.
2117              j      True if the number of jobs is at least n.
2118              L      True if the SHLVL parameter is at least n.
2119              l      True  if  at least n characters have already been printed
2120                     on the current line.  When n  is  negative,  true  if  at
2121                     least abs(n) characters remain before the opposite margin
2122                     (thus the left margin for RPROMPT).
2123              S      True if the SECONDS parameter is at least n.
2124              T      True if the time in hours is equal to n.
2125              t      True if the time in minutes is equal to n.
2126              v      True if the array psvar has at least n elements.
2127              V      True  if  element  n  of  the  array  psvar  is  set  and
2128                     non-empty.
2129              w      True if the day of the week is equal to n (Sunday = 0).
2130
2131       %<string<
2132       %>string>
2133       %[xstring]
2134              Specifies  truncation  behaviour for the remainder of the prompt
2135              string.   The  third,  deprecated,   form   is   equivalent   to
2136              `%xstringx',  i.e. x may be `<' or `>'.  The string will be dis‐
2137              played in place of the truncated portion  of  any  string;  note
2138              this does not undergo prompt expansion.
2139
2140              The numeric argument, which in the third form may appear immedi‐
2141              ately after the `[', specifies the maximum permitted  length  of
2142              the various strings that can be displayed in the prompt.  In the
2143              first two forms, this numeric argument may be negative, in which
2144              case  the  truncation  length  is  determined by subtracting the
2145              absolute value of the numeric argument from the number of  char‐
2146              acter  positions  remaining on the current prompt line.  If this
2147              results in a zero or negative length, a length of 1 is used.  In
2148              other  words, a negative argument arranges that after truncation
2149              at least n characters remain before the right margin (left  mar‐
2150              gin for RPROMPT).
2151
2152              The  forms  with `<' truncate at the left of the string, and the
2153              forms with `>' truncate at the right of the string.   For  exam‐
2154              ple,  if  the  current  directory  is  `/home/pike',  the prompt
2155              `%8<..<%/' will expand to `..e/pike'.  In this string, the  ter‐
2156              minating  character (`<', `>' or `]'), or in fact any character,
2157              may be quoted by a preceding `\'; note when using print -P, how‐
2158              ever, that this must be doubled as the string is also subject to
2159              standard  print  processing,  in  addition  to  any  backslashes
2160              removed  by a double quoted string:  the worst case is therefore
2161              `print -P "%<\\\\<<..."'.
2162
2163              If the string is longer than the specified truncation length, it
2164              will appear in full, completely replacing the truncated string.
2165
2166              The part of the prompt string to be truncated runs to the end of
2167              the string, or to the end of the next  enclosing  group  of  the
2168              `%('  construct,  or  to  the next truncation encountered at the
2169              same grouping level (i.e. truncations inside a  `%('  are  sepa‐
2170              rate), which ever comes first.  In particular, a truncation with
2171              argument zero (e.g., `%<<') marks the end of the  range  of  the
2172              string  to  be truncated while turning off truncation from there
2173              on. For example, the prompt  `%10<...<%~%<<%#  '  will  print  a
2174              truncated representation of the current directory, followed by a
2175              `%' or `#', followed by a space.  Without the `%<<',  those  two
2176              characters  would  be  included  in  the string to be truncated.
2177              Note that `%-0<<' is not equivalent to `%<<' but specifies  that
2178              the prompt is truncated at the right margin.
2179
2180              Truncation  applies  only  within  each  individual  line of the
2181              prompt, as delimited by embedded  newlines  (if  any).   If  the
2182              total  length  of  any  line  of  the prompt after truncation is
2183              greater than the terminal width, or if the part to be  truncated
2184              contains embedded newlines, truncation behavior is undefined and
2185              may  change  in  a   future   version   of   the   shell.    Use
2186              `%-n(l.true-text.false-text)' to remove parts of the prompt when
2187              the available space is less than n.
2188
2189
2190
2191zsh 5.5.1                       April 16, 2018                      ZSHMISC(1)
Impressum