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 (re‐
50       turns a zero status).  If two pipelines are separated by `||', the sec‐
51       ond  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  be‐
69       fore  executing the next sublist.  If a sublist is terminated by a `&',
70       `&|', or `&!', the shell executes the last pipeline in it in the  back‐
71       ground,  and  does  not wait for it to finish (note the difference from
72       other shells which execute the whole sublist  in  the  background).   A
73       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 de‐
98              fault  path to be searched instead of that in $path. With the -v
99              flag, command is similar to whence and with -V, it is equivalent
100              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 ef‐
125              fect 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              Expand the list of words, and set the parameter name to each  of
141              them  in  turn,  executing  list each time.  If the `in word' is
142              omitted, use the positional parameters instead of the words.
143
144              The term consists of one or more newline or  ;  which  terminate
145              the words, and are optional when the `in word' is omitted.
146
147              More  than  one  parameter  name  can  appear before the list of
148              words.  If N names are given, then on each execution of the loop
149              the  next  N words are assigned to the corresponding parameters.
150              If there are more names than remaining words, the remaining  pa‐
151              rameters  are  each  set  to the empty string.  Execution of the
152              loop ends when there is no remaining word to assign to the first
153              name.  It is only possible for in to appear as the first name in
154              the list, else it will be treated as  marking  the  end  of  the
155              list.
156
157       for (( [expr1] ; [expr2] ; [expr3] )) do list done
158              The arithmetic expression expr1 is evaluated first (see the sec‐
159              tion `Arithmetic Evaluation').  The arithmetic expression  expr2
160              is  repeatedly  evaluated  until  it  evaluates to zero and when
161              non-zero, list is executed and the arithmetic  expression  expr3
162              evaluated.   If any expression is omitted, then it behaves as if
163              it evaluated to 1.
164
165       while list do list done
166              Execute the do list as long as the while  list  returns  a  zero
167              exit status.
168
169       until list do list done
170              Execute the do list as long as until list returns a nonzero exit
171              status.
172
173       repeat word do list done
174              word is expanded and treated as an arithmetic expression,  which
175              must evaluate to a number n.  list is then executed n times.
176
177              The  repeat  syntax is disabled by default when the shell starts
178              in a mode emulating another shell.  It can be enabled  with  the
179              command `enable -r repeat'
180
181       case  word  in  [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ...
182       esac
183              Execute the list associated with the first pattern that  matches
184              word, if any.  The form of the patterns is the same as that used
185              for filename generation.  See the section `Filename Generation'.
186
187              Note further that, unless the SH_GLOB option is set,  the  whole
188              pattern  with alternatives is treated by the shell as equivalent
189              to a group of patterns within parentheses, although white  space
190              may  appear  about the parentheses and the vertical bar and will
191              be stripped from the pattern at those points.  White  space  may
192              appear  elsewhere  in the pattern; this is not stripped.  If the
193              SH_GLOB option is set, so that an opening parenthesis can be un‐
194              ambiguously  treated  as part of the case syntax, the expression
195              is parsed into separate words and these are  treated  as  strict
196              alternatives (as in other shells).
197
198              If  the  list that is executed is terminated with ;& rather than
199              ;;, the following list is also executed.  The rule for the  ter‐
200              minator of the following list ;;, ;& or ;| is applied unless the
201              esac is reached.
202
203              If the list that is executed is terminated  with  ;|  the  shell
204              continues  to scan the patterns looking for the next match, exe‐
205              cuting the corresponding list, and applying  the  rule  for  the
206              corresponding  terminator  ;;,  ;& or ;|.  Note that word is not
207              re-expanded; all applicable patterns are tested  with  the  same
208              word.
209
210       select name [ in word ... term ] do list done
211              where  term  is one or more newline or ; to terminate the words.
212              Print the set of words, each preceded by a number.   If  the  in
213              word  is  omitted,  use  the positional parameters.  The PROMPT3
214              prompt is printed and a line is read from the line editor if the
215              shell is interactive and that is active, or else standard input.
216              If this line consists of the number of one of the listed  words,
217              then the parameter name is set to the word corresponding to this
218              number.  If this line is empty, the selection  list  is  printed
219              again.   Otherwise,  the  value  of the parameter name is set to
220              null.  The contents of the line  read  from  standard  input  is
221              saved  in the parameter REPLY.  list is executed for each selec‐
222              tion until a break or end-of-file is encountered.
223
224       ( list )
225              Execute list in a subshell.  Traps set by the trap  builtin  are
226              reset to their default values while executing list; an exception
227              is that ignored signals will continue to be ignored if  the  op‐
228              tion POSIXTRAPS is set.
229
230       { list }
231              Execute list.
232
233       { try-list } always { always-list }
234              First  execute try-list.  Regardless of errors, or break or con‐
235              tinue commands encountered within try-list, execute always-list.
236              Execution  then  continues  from  the result of the execution of
237              try-list; in other words, any error, or break or  continue  com‐
238              mand  is  treated  in the normal way, as if always-list were not
239              present.  The two chunks of code are referred  to  as  the  `try
240              block' and the `always block'.
241
242              Optional  newlines  or  semicolons  may appear after the always;
243              note, however, that they may not appear  between  the  preceding
244              closing brace and the always.
245
246              An `error' in this context is a condition such as a syntax error
247              which causes the shell to abort execution of the  current  func‐
248              tion,  script,  or  list.   Syntax  errors encountered while the
249              shell is parsing the code do not cause the always-list to be ex‐
250              ecuted.   For  example,  an  erroneously constructed if block in
251              try-list would cause the shell to abort during parsing, so  that
252              always-list  would not be executed, while an erroneous substitu‐
253              tion such as ${*foo*} would cause a run-time error, after  which
254              always-list would be executed.
255
256              An  error condition can be tested and reset with the special in‐
257              teger variable  TRY_BLOCK_ERROR.   Outside  an  always-list  the
258              value  is  irrelevant,  but it is initialised to -1.  Inside al‐
259              ways-list, the value is 1 if an error occurred in the  try-list,
260              else  0.  If TRY_BLOCK_ERROR is set to 0 during the always-list,
261              the error condition caused by the try-list is reset,  and  shell
262              execution  continues normally after the end of always-list.  Al‐
263              tering the value during the try-list is not useful (unless  this
264              forms part of an enclosing always block).
265
266              Regardless  of TRY_BLOCK_ERROR, after the end of always-list the
267              normal shell status $? is  the  value  returned  from  try-list.
268              This   will   be  non-zero  if  there  was  an  error,  even  if
269              TRY_BLOCK_ERROR was set to zero.
270
271              The following executes the given code, ignoring  any  errors  it
272              causes.   This is an alternative to the usual convention of pro‐
273              tecting code by executing it in a subshell.
274
275                     {
276                         # code which may cause an error
277                       } always {
278                         # This code is executed regardless of the error.
279                         (( TRY_BLOCK_ERROR = 0 ))
280                     }
281                     # The error condition has been reset.
282
283              When a try block occurs outside of any function, a return  or  a
284              exit encountered in try-list does not cause the execution of al‐
285              ways-list.  Instead, the shell exits immediately after any  EXIT
286              trap has been executed.  Otherwise, a return command encountered
287              in try-list will cause the execution of always-list,  just  like
288              break and continue.
289
290       function [ -T ] word ... [ () ] [ term ] { list }
291       word ... () [ term ] { list }
292       word ... () [ term ] command
293              where term is one or more newline or ;.  Define a function which
294              is referenced by any one of word.  Normally, only  one  word  is
295              provided;  multiple  words  are  usually only useful for setting
296              traps.  The body of the function is the list between the  {  and
297              }.  See the section `Functions'.
298
299              The options of function have the following meanings:
300
301              -T     Enable  tracing  for  this function, as though with func‐
302                     tions -T.  See the documentation of the -f option to  the
303                     typeset builtin, in zshbuiltins(1).
304
305              If  the  option  SH_GLOB  is  set  for  compatibility with other
306              shells, then whitespace may appear between the  left  and  right
307              parentheses  when there is a single word;  otherwise, the paren‐
308              theses will be treated as forming a  globbing  pattern  in  that
309              case.
310
311              In  any of the forms above, a redirection may appear outside the
312              function body, for example
313
314                     func() { ... } 2>&1
315
316              The redirection is stored with the function and applied whenever
317              the  function is executed.  Any variables in the redirection are
318              expanded at the point the function is executed, but outside  the
319              function scope.
320
321       time [ pipeline ]
322              The  pipeline is executed, and timing statistics are reported on
323              the standard error in the form specified by the TIMEFMT  parame‐
324              ter.   If  pipeline is omitted, print statistics about the shell
325              process and its children.
326
327       [[ exp ]]
328              Evaluates the conditional expression exp and return a zero  exit
329              status if it is true.  See the section `Conditional Expressions'
330              for a description of exp.
331

ALTERNATE FORMS FOR COMPLEX COMMANDS

333       Many of  zsh's  complex  commands  have  alternate  forms.   These  are
334       non-standard  and  are  likely not to be obvious even to seasoned shell
335       programmers; they should not be used anywhere that portability of shell
336       code is a concern.
337
338       The short versions below only work if sublist is of the form `{ list }'
339       or if the SHORT_LOOPS option is set.  For the if, while and until  com‐
340       mands, in both these cases the test part of the loop must also be suit‐
341       ably delimited, such as by `[[ ... ]]' or `(( ... ))', else the end  of
342       the  test will not be recognized.  For the for, repeat, case and select
343       commands no such special form for the arguments is necessary,  but  the
344       other  condition (the special form of sublist or use of the SHORT_LOOPS
345       option) still applies.  The SHORT_REPEAT option is available to  enable
346       the short version only for the repeat command.
347
348       if list { list } [ elif list { list } ] ... [ else { list } ]
349              An alternate form of if.  The rules mean that
350
351                     if [[ -o ignorebraces ]] {
352                       print yes
353                     }
354
355              works, but
356
357                     if true {  # Does not work!
358                       print yes
359                     }
360
361              does not, since the test is not suitably delimited.
362
363       if list sublist
364              A  short  form of the alternate if.  The same limitations on the
365              form of list apply as for the previous form.
366
367       for name ... ( word ... ) sublist
368              A short form of for.
369
370       for name ... [ in word ... ] term sublist
371              where term is at least one newline or ;.  Another short form  of
372              for.
373
374       for (( [expr1] ; [expr2] ; [expr3] )) sublist
375              A short form of the arithmetic for command.
376
377       foreach name ... ( word ... ) list end
378              Another form of for.
379
380       while list { list }
381              An  alternative form of while.  Note the limitations on the form
382              of list mentioned above.
383
384       until list { list }
385              An alternative form of until.  Note the limitations on the  form
386              of list mentioned above.
387
388       repeat word sublist
389              This is a short form of repeat.
390
391       case word { [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ... }
392              An alternative form of case.
393
394       select name [ in word ... term ] sublist
395              where  term  is  at least one newline or ;.  A short form of se‐
396              lect.
397
398       function word ... [ () ] [ term ] sublist
399              This is a short form of function.
400

RESERVED WORDS

402       The following words are recognized as reserved words when used  as  the
403       first word of a command unless quoted or disabled using disable -r:
404
405       do  done  esac then elif else fi for case if while function repeat time
406       until select coproc nocorrect foreach end ! [[ { } declare export float
407       integer local readonly typeset
408
409       Additionally,  `}'  is  recognized  in  any position if neither the IG‐
410       NORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.
411

ERRORS

413       Certain errors are treated as fatal by the  shell:  in  an  interactive
414       shell,  they  cause  control  to  return  to the command line, and in a
415       non-interactive shell they cause the shell to  be  aborted.   In  older
416       versions  of  zsh,  a  non-interactive shell running a script would not
417       abort completely, but would resume execution at the next command to  be
418       read  from the script, skipping the remainder of any functions or shell
419       constructs such as loops or conditions; this somewhat illogical  behav‐
420       iour can be recovered by setting the option CONTINUE_ON_ERROR.
421
422       Fatal errors found in non-interactive shells include:
423
424       •      Failure to parse shell options passed when invoking the shell
425
426       •      Failure to change options with the set builtin
427
428       •      Parse errors of all sorts, including failures to parse mathemat‐
429              ical expressions
430
431       •      Failures to set or modify variable behaviour with  typeset,  lo‐
432              cal, declare, export, integer, float
433
434       •      Execution  of  incorrectly  positioned  loop  control structures
435              (continue, break)
436
437       •      Attempts to use regular expression with  no  regular  expression
438              module available
439
440       •      Disallowed operations when the RESTRICTED options is set
441
442       •      Failure to create a pipe needed for a pipeline
443
444       •      Failure to create a multio
445
446       •      Failure to autoload a module needed for a declared shell feature
447
448       •      Errors creating command or process substitutions
449
450       •      Syntax errors in glob qualifiers
451
452       •      File  generation  errors where not caught by the option BAD_PAT‐
453              TERN
454
455       •      All bad patterns used for matching within case statements
456
457       •      File generation failures where not caused by NO_MATCH or similar
458              options
459
460       •      All  file generation errors where the pattern was used to create
461              a multio
462
463       •      Memory errors where detected by the shell
464
465       •      Invalid subscripts to shell variables
466
467       •      Attempts to assign read-only variables
468
469       •      Logical errors with variables such as assignment  to  the  wrong
470              type
471
472       •      Use of invalid variable names
473
474       •      Errors in variable substitution syntax
475
476       •      Failure to convert characters in $'...' expressions
477
478       If  the POSIX_BUILTINS option is set, more errors associated with shell
479       builtin commands are treated as fatal, as specified by the POSIX  stan‐
480       dard.
481

COMMENTS

483       In  non-interactive  shells, or in interactive shells with the INTERAC‐
484       TIVE_COMMENTS option set, a word beginning with the third character  of
485       the  histchars  parameter (`#' by default) causes that word and all the
486       following characters up to a newline to be ignored.
487

ALIASING

489       Every eligible word in the shell input is checked to see if there is an
490       alias  defined  for it.  If so, it is replaced by the text of the alias
491       if it is in command position (if it could be the first word of a simple
492       command), or if the alias is global.  If the replacement text ends with
493       a space, the next word in the shell input is always eligible  for  pur‐
494       poses of alias expansion.
495
496       It  is an error for the function name, word, in the sh-compatible func‐
497       tion definition syntax `word () ...' to be a word  that  resulted  from
498       alias expansion, unless the ALIAS_FUNC_DEF option is set.
499
500       An  alias is defined using the alias builtin; global aliases may be de‐
501       fined using the -g option to that builtin.
502
503       A word is defined as:
504
505       •      Any plain string or glob pattern
506
507       •      Any quoted string, using  any  quoting  method  (note  that  the
508              quotes  must be part of the alias definition for this to be eli‐
509              gible)
510
511       •      Any parameter reference or command substitution
512
513       •      Any series of the foregoing, concatenated without whitespace  or
514              other tokens between them
515
516       •      Any reserved word (case, do, else, etc.)
517
518       •      With global aliasing, any command separator, any redirection op‐
519              erator, and `(' or `)' when not part of a glob pattern
520
521       Alias expansion is done on the shell input before any  other  expansion
522       except  history  expansion.   Therefore, if an alias is defined for the
523       word foo, alias expansion may be avoided by quoting part of  the  word,
524       e.g.  \foo.   Any  form  of quoting works, although there is nothing to
525       prevent an alias being defined for the quoted  form  such  as  \foo  as
526       well.
527
528       In particular, note that quoting must be used when using unalias to re‐
529       move global aliases:
530
531              % alias -g foo=bar
532              % unalias foo
533              unalias: no such hash table element: bar
534              % unalias \foo
535              %
536
537       When POSIX_ALIASES is set, only plain unquoted strings are eligible for
538       aliasing.   The  alias  builtin does not reject ineligible aliases, but
539       they are not expanded.
540
541       For use with completion, which would remove an initial  backslash  fol‐
542       lowed  by  a character that isn't special, it may be more convenient to
543       quote the word by starting with a single quote, i.e.  'foo;  completion
544       will automatically add the trailing single quote.
545
546   Alias difficulties
547       Although aliases can be used in ways that bend normal shell syntax, not
548       every string of non-white-space characters can be used as an alias.
549
550       Any set of characters not listed as a word above is not a  word,  hence
551       no  attempt  is  made to expand it as an alias, no matter how it is de‐
552       fined (i.e. via the builtin or the special parameter aliases  described
553       in the section THE ZSH/PARAMETER MODULE in zshmodules(1)).  However, as
554       noted in the case of POSIX_ALIASES above, the shell does not attempt to
555       deduce  whether  the string corresponds to a word at the time the alias
556       is created.
557
558       For example, an expression containing an = at the start  of  a  command
559       line  is  an assignment and cannot be expanded as an alias; a lone = is
560       not an assignment but can only be set as an alias using the  parameter,
561       as otherwise the = is taken part of the syntax of the builtin command.
562
563       It  is  not  presently possible to alias the `((' token that introduces
564       arithmetic expressions, because until a full statement has been parsed,
565       it  cannot be distinguished from two consecutive `(' tokens introducing
566       nested subshells.  Also, if a separator such  as  &&  is  aliased,  \&&
567       turns into the two tokens \& and &, each of which may have been aliased
568       separately.  Similarly for \<<, \>|, etc.
569
570       There is a commonly encountered problem with aliases illustrated by the
571       following code:
572
573              alias echobar='echo bar'; echobar
574
575       This  prints  a  message  that  the command echobar could not be found.
576       This happens because aliases are expanded when the code is read in; the
577       entire  line  is read in one go, so that when echobar is executed it is
578       too late to expand the newly defined alias.  This is often a problem in
579       shell scripts, functions, and code executed with `source' or `.'.  Con‐
580       sequently, use of functions  rather  than  aliases  is  recommended  in
581       non-interactive code.
582

QUOTING

584       A  character  may be quoted (that is, made to stand for itself) by pre‐
585       ceding it with a `\'.  `\' followed by a newline is ignored.
586
587       A string enclosed between `$'' and `'' is processed the same way as the
588       string arguments of the print builtin, and the resulting string is con‐
589       sidered to be entirely quoted.  A literal `'' character can be included
590       in the string by using the `\'' escape.
591
592       All  characters  enclosed  between a pair of single quotes ('') that is
593       not preceded by a `$' are quoted.  A single quote cannot appear  within
594       single  quotes unless the option RC_QUOTES is set, in which case a pair
595       of single quotes are turned into a single quote.  For example,
596
597              print ''''
598
599       outputs nothing apart from a newline if RC_QUOTES is not set,  but  one
600       single quote if it is set.
601
602       Inside  double  quotes  (""), parameter and command substitution occur,
603       and `\' quotes the characters `\', ``', `"', `$', and the first charac‐
604       ter of $histchars (default `!').
605

REDIRECTION

607       If  a  command is followed by & and job control is not active, then the
608       default standard input for the command is  the  empty  file  /dev/null.
609       Otherwise,  the environment for the execution of a command contains the
610       file descriptors of the invoking  shell  as  modified  by  input/output
611       specifications.
612
613       The following may appear anywhere in a simple command or may precede or
614       follow a complex command.  Expansion occurs before  word  or  digit  is
615       used except as noted below.  If the result of substitution on word pro‐
616       duces more than one filename,  redirection  occurs  for  each  separate
617       filename in turn.
618
619       < word Open file word for reading as standard input.  It is an error to
620              open a file in this fashion if it does not exist.
621
622       <> word
623              Open file word for reading and writing as  standard  input.   If
624              the file does not exist then it is created.
625
626       > word Open file word for writing as standard output.  If the file does
627              not exist then it is created.  If the file exists, and the CLOB‐
628              BER  option  is  unset,  this  causes an error; otherwise, it is
629              truncated to zero length.
630
631       >| word
632       >! word
633              Same as >, except that the file is truncated to zero  length  if
634              it exists, regardless of CLOBBER.
635
636       >> word
637              Open  file  word  for writing in append mode as standard output.
638              If the file does not exist, and the  CLOBBER  and  APPEND_CREATE
639              options  are  both  unset,  this causes an error; otherwise, the
640              file is created.
641
642       >>| word
643       >>! word
644              Same as >>, except that the file is created if it does  not  ex‐
645              ist, regardless of CLOBBER and APPEND_CREATE.
646
647       <<[-] word
648              The  shell  input is read up to a line that is the same as word,
649              or to an end-of-file.  No parameter expansion, command substitu‐
650              tion or filename generation is performed on word.  The resulting
651              document, called a here-document, becomes the standard input.
652
653              If any character of word is quoted with single or double  quotes
654              or a `\', no interpretation is placed upon the characters of the
655              document.  Otherwise, parameter and command substitution occurs,
656              `\'  followed  by  a newline is removed, and `\' must be used to
657              quote the characters `\', `$', ``' and the  first  character  of
658              word.
659
660              Note  that  word itself does not undergo shell expansion.  Back‐
661              quotes in word do not have their usual effect; instead they  be‐
662              have  similarly  to  double  quotes,  except that the backquotes
663              themselves are passed through unchanged.  (This  information  is
664              given for completeness and it is not recommended that backquotes
665              be used.)  Quotes in the form $'...' have their standard  effect
666              of expanding backslashed references to special characters.
667
668              If <<- is used, then all leading tabs are stripped from word and
669              from the document.
670
671       <<< word
672              Perform shell expansion on word and pass the result to  standard
673              input.  This is known as a here-string.  Compare the use of word
674              in here-documents above, where word does not undergo  shell  ex‐
675              pansion.  The result will have a trailing newline after it.
676
677       <& number
678       >& number
679              The  standard  input/output  is  duplicated from file descriptor
680              number (see dup2(2)).
681
682       <& -
683       >& -   Close the standard input/output.
684
685       <& p
686       >& p   The input/output from/to the coprocess is moved to the  standard
687              input/output.
688
689       >& word
690       &> word
691              (Except  where `>& word' matches one of the above syntaxes; `&>'
692              can always be used to avoid  this  ambiguity.)   Redirects  both
693              standard  output  and  standard error (file descriptor 2) in the
694              manner of `> word'.  Note that this does not have the  same  ef‐
695              fect  as  `> word 2>&1' in the presence of multios (see the sec‐
696              tion below).
697
698       >&| word
699       >&! word
700       &>| word
701       &>! word
702              Redirects both standard output and standard error (file descrip‐
703              tor 2) in the manner of `>| word'.
704
705       >>& word
706       &>> word
707              Redirects both standard output and standard error (file descrip‐
708              tor 2) in the manner of `>> word'.
709
710       >>&| word
711       >>&! word
712       &>>| word
713       &>>! word
714              Redirects both standard output and standard error (file descrip‐
715              tor 2) in the manner of `>>| word'.
716
717       If  one  of  the above is preceded by a digit, then the file descriptor
718       referred to is that specified by the digit instead of the default 0  or
719       1.   The order in which redirections are specified is significant.  The
720       shell evaluates each redirection in  terms  of  the  (file  descriptor,
721       file) association at the time of evaluation.  For example:
722
723              ... 1>fname 2>&1
724
725       first associates file descriptor 1 with file fname.  It then associates
726       file descriptor 2 with the file associated with file descriptor 1 (that
727       is,  fname).  If the order of redirections were reversed, file descrip‐
728       tor 2 would be associated with the terminal (assuming file descriptor 1
729       had  been)  and  then  file  descriptor 1 would be associated with file
730       fname.
731
732       The `|&' command separator described in Simple Commands & Pipelines  in
733       zshmisc(1) is a shorthand for `2>&1 |'.
734
735       The various forms of process substitution, `<(list)', and `=(list)' for
736       input and `>(list)' for output, are often used together with  redirect‐
737       ion.   For  example,  if  word  in an output redirection is of the form
738       `>(list)' then the output is piped to the command represented by  list.
739       See Process Substitution in zshexpn(1).
740

OPENING FILE DESCRIPTORS USING PARAMETERS

742       When  the shell is parsing arguments to a command, and the shell option
743       IGNORE_BRACES is not set, a different form of redirection  is  allowed:
744       instead  of  a digit before the operator there is a valid shell identi‐
745       fier enclosed in braces.  The shell will open  a  new  file  descriptor
746       that is guaranteed to be at least 10 and set the parameter named by the
747       identifier to the file descriptor opened.  No whitespace is allowed be‐
748       tween the closing brace and the redirection character.  For example:
749
750              ... {myfd}>&1
751
752       This opens a new file descriptor that is a duplicate of file descriptor
753       1 and sets the parameter myfd to the number  of  the  file  descriptor,
754       which  will  be at least 10.  The new file descriptor can be written to
755       using the syntax >&$myfd.  The file descriptor  remains  open  in  sub‐
756       shells and forked external executables.
757
758       The  syntax  {varid}>&-,  for example {myfd}>&-, may be used to close a
759       file descriptor opened in this fashion.  Note that the parameter  given
760       by varid must previously be set to a file descriptor in this case.
761
762       It  is an error to open or close a file descriptor in this fashion when
763       the parameter is readonly.  However, it is not  an  error  to  read  or
764       write  a  file  descriptor using <&$param or >&$param if param is read‐
765       only.
766
767       If the option CLOBBER is unset, it is an error to open a file  descrip‐
768       tor  using  a  parameter that is already set to an open file descriptor
769       previously allocated by this mechanism.  Unsetting the parameter before
770       using it for allocating a file descriptor avoids the error.
771
772       Note  that this mechanism merely allocates or closes a file descriptor;
773       it does not perform any redirections from or to it.  It is usually con‐
774       venient  to  allocate  a file descriptor prior to use as an argument to
775       exec.  The syntax does not in any case work when  used  around  complex
776       commands  such  as  parenthesised subshells or loops, where the opening
777       brace is interpreted as part of a command list to be  executed  in  the
778       current shell.
779
780       The  following shows a typical sequence of allocation, use, and closing
781       of a file descriptor:
782
783              integer myfd
784              exec {myfd}>~/logs/mylogfile.txt
785              print This is a log message. >&$myfd
786              exec {myfd}>&-
787
788       Note that the expansion of the variable in the expression  >&$myfd  oc‐
789       curs  at the point the redirection is opened.  This is after the expan‐
790       sion of command arguments and after any redirections to the left on the
791       command line have been processed.
792

MULTIOS

794       If the user tries to open a file descriptor for writing more than once,
795       the shell opens the file descriptor as a pipe to a process that  copies
796       its  input  to  all the specified outputs, similar to tee, provided the
797       MULTIOS option is set, as it is by default.  Thus:
798
799              date >foo >bar
800
801       writes the date to two files, named `foo' and `bar'.  Note that a  pipe
802       is an implicit redirection; thus
803
804              date >foo | cat
805
806       writes the date to the file `foo', and also pipes it to cat.
807
808       Note  that  the  shell  opens  all  the  files to be used in the multio
809       process immediately, not at the point they are about to be written.
810
811       Note also that redirections are always expanded in order.  This happens
812       regardless of the setting of the MULTIOS option, but with the option in
813       effect there are additional consequences. For example, the  meaning  of
814       the expression >&1 will change after a previous redirection:
815
816              date >&1 >output
817
818       In  the  case above, the >&1 refers to the standard output at the start
819       of the line; the result is similar to the tee command.   However,  con‐
820       sider:
821
822              date >output >&1
823
824       As redirections are evaluated in order, when the >&1 is encountered the
825       standard output is set to the file output and another copy of the  out‐
826       put is therefore sent to that file.  This is unlikely to be what is in‐
827       tended.
828
829       If the MULTIOS option is set, the word after a redirection operator  is
830       also subjected to filename generation (globbing).  Thus
831
832              : > *
833
834       will  truncate  all files in the current directory, assuming there's at
835       least one.  (Without the MULTIOS option, it would create an empty  file
836       called `*'.)  Similarly, you can do
837
838              echo exit 0 >> *.sh
839
840       If the user tries to open a file descriptor for reading more than once,
841       the shell opens the file descriptor as a pipe to a process that  copies
842       all the specified inputs to its output in the order specified, provided
843       the MULTIOS option is set.  It should be noted that each file is opened
844       immediately, not at the point where it is about to be read: this behav‐
845       iour differs from cat, so if strictly standard behaviour is needed, cat
846       should be used instead.
847
848       Thus
849
850              sort <foo <fubar
851
852       or even
853
854              sort <f{oo,ubar}
855
856       is equivalent to `cat foo fubar | sort'.
857
858       Expansion of the redirection argument occurs at the point the redirect‐
859       ion is opened, at the point described above for the  expansion  of  the
860       variable in >&$myfd.
861
862       Note that a pipe is an implicit redirection; thus
863
864              cat bar | sort <foo
865
866       is equivalent to `cat bar foo | sort' (note the order of the inputs).
867
868       If  the MULTIOS option is unset, each redirection replaces the previous
869       redirection for that file descriptor.  However, all files redirected to
870       are actually opened, so
871
872              echo Hello > bar > baz
873
874       when  MULTIOS  is  unset  will  truncate  `bar', and write `Hello' into
875       `baz'.
876
877       There is a problem when an output multio is  attached  to  an  external
878       program.  A simple example shows this:
879
880              cat file >file1 >file2
881              cat file1 file2
882
883       Here,  it  is  possible that the second `cat' will not display the full
884       contents of file1 and file2 (i.e. the original  contents  of  file  re‐
885       peated twice).
886
887       The  reason  for  this  is  that  the multios are spawned after the cat
888       process is forked from the parent shell, so the parent shell  does  not
889       wait for the multios to finish writing data.  This means the command as
890       shown can exit before file1 and file2 are  completely  written.   As  a
891       workaround,  it  is possible to run the cat process as part of a job in
892       the current shell:
893
894              { cat file } >file >file2
895
896       Here, the {...} job will pause to wait for both files to be written.
897

REDIRECTIONS WITH NO COMMAND

899       When a simple command consists of one or more redirection operators and
900       zero or more parameter assignments, but no command name, zsh can behave
901       in several ways.
902
903       If the parameter NULLCMD is not set or the option CSH_NULLCMD  is  set,
904       an error is caused.  This is the csh behavior and CSH_NULLCMD is set by
905       default when emulating csh.
906
907       If the option SH_NULLCMD is set, the builtin `:' is inserted as a  com‐
908       mand  with  the given redirections.  This is the default when emulating
909       sh or ksh.
910
911       Otherwise, if the parameter NULLCMD is set, its value will be used as a
912       command  with  the given redirections.  If both NULLCMD and READNULLCMD
913       are set, then the value of the latter will be used instead of  that  of
914       the  former  when the redirection is an input.  The default for NULLCMD
915       is `cat' and for READNULLCMD is `more'. Thus
916
917              < file
918
919       shows the contents of file on standard output, with paging if that is a
920       terminal.  NULLCMD and READNULLCMD may refer to shell functions.
921

COMMAND EXECUTION

923       If a command name contains no slashes, the shell attempts to locate it.
924       If there exists a shell function by that name, the function is  invoked
925       as  described  in  the  section  `Functions'.   If there exists a shell
926       builtin by that name, the builtin is invoked.
927
928       Otherwise, the shell searches each element of  $path  for  a  directory
929       containing an executable file by that name.
930
931       If execution fails: an error message is printed, and one of the follow‐
932       ing values is returned.
933
934       127    The search was unsuccessful.  The error message is `command  not
935              found: cmd'.
936       126    The executable file has insufficient permissions, is a directory
937              or special file, or is not a script and is in a format  unrecog‐
938              nized  by  the operating system.  The exact conditions and error
939              message are operating system-dependent; see execve(2).
940
941       If execution fails because the file is not in  executable  format,  and
942       the  file  is  not  a  directory,  it  is assumed to be a shell script.
943       /bin/sh is spawned to execute it.  If the program is a  file  beginning
944       with `#!', the remainder of the first line specifies an interpreter for
945       the program.  The shell will execute the specified interpreter on oper‐
946       ating systems that do not handle this executable format in the kernel.
947
948       If  no  external command is found but a function command_not_found_han‐
949       dler exists the shell executes this function with all command line  ar‐
950       guments.   The  return status of the function becomes the status of the
951       command.  Note that the handler is executed in a subshell forked to ex‐
952       ecute  an external command, hence changes to directories, shell parame‐
953       ters, etc. have no effect on the main shell.
954

FUNCTIONS

956       Shell functions are defined with the function reserved word or the spe‐
957       cial  syntax `funcname ()'.  Shell functions are read in and stored in‐
958       ternally.  Alias names are resolved when the function is  read.   Func‐
959       tions  are  executed  like  commands with the arguments passed as posi‐
960       tional parameters.  (See the section `Command Execution'.)
961
962       Functions execute in the same process as the caller and share all files
963       and  present working directory with the caller.  A trap on EXIT set in‐
964       side a function is executed after the function completes in  the  envi‐
965       ronment of the caller.
966
967       The return builtin is used to return from function calls.
968
969       Function  identifiers  can be listed with the functions builtin.  Func‐
970       tions can be undefined with the unfunction builtin.
971

AUTOLOADING FUNCTIONS

973       A function can be marked as undefined using the  autoload  builtin  (or
974       `functions  -u'  or `typeset -fu').  Such a function has no body.  When
975       the function is first executed, the shell searches for  its  definition
976       using the elements of the fpath variable.  Thus to define functions for
977       autoloading, a typical sequence is:
978
979              fpath=(~/myfuncs $fpath)
980              autoload myfunc1 myfunc2 ...
981
982       The usual alias expansion during reading will be suppressed if the  au‐
983       toload builtin or its equivalent is given the option -U. This is recom‐
984       mended for the use of functions supplied  with  the  zsh  distribution.
985       Note  that  for functions precompiled with the zcompile builtin command
986       the flag -U must be provided when the .zwc file is created, as the cor‐
987       responding information is compiled into the latter.
988
989       For  each  element  in fpath, the shell looks for three possible files,
990       the newest of which is used to load the definition for the function:
991
992       element.zwc
993              A file created with the zcompile builtin command, which  is  ex‐
994              pected  to  contain the definitions for all functions in the di‐
995              rectory named element.  The file is treated in the  same  manner
996              as  a  directory  containing files for functions and is searched
997              for the definition of the function.   If the definition  is  not
998              found,  the  search for a definition proceeds with the other two
999              possibilities described below.
1000
1001              If element already includes a .zwc extension (i.e. the extension
1002              was  explicitly  given by the user), element is searched for the
1003              definition of the function without comparing its age to that  of
1004              other  files;  in  fact, there does not need to be any directory
1005              named element without the suffix.   Thus  including  an  element
1006              such as `/usr/local/funcs.zwc' in fpath will speed up the search
1007              for functions, with the  disadvantage  that  functions  included
1008              must  be  explicitly recompiled by hand before the shell notices
1009              any changes.
1010
1011       element/function.zwc
1012              A file created with zcompile, which is expected to  contain  the
1013              definition  for function.  It may include other function defini‐
1014              tions as well, but those are neither loaded nor executed; a file
1015              found  in  this way is searched only for the definition of func‐
1016              tion.
1017
1018       element/function
1019              A file of zsh command text, taken to be the definition for func‐
1020              tion.
1021
1022       In  summary, the order of searching is, first, in the parents of direc‐
1023       tories in fpath for the newer of either a compiled directory or  a  di‐
1024       rectory  in fpath; second, if more than one of these contains a defini‐
1025       tion for the function that is sought, the leftmost in the fpath is cho‐
1026       sen;  and  third,  within  a  directory, the newer of either a compiled
1027       function or an ordinary function definition is used.
1028
1029       If the KSH_AUTOLOAD option is set, or the file contains only  a  simple
1030       definition of the function, the file's contents will be executed.  This
1031       will normally define the function in question,  but  may  also  perform
1032       initialization, which is executed in the context of the function execu‐
1033       tion, and may therefore define local parameters.  It is an error if the
1034       function is not defined by loading the file.
1035
1036       Otherwise,  the  function body (with no surrounding `funcname() {...}')
1037       is taken to be the complete contents of the file.  This form allows the
1038       file  to be used directly as an executable shell script.  If processing
1039       of the file results in the function being re-defined, the function  it‐
1040       self  is not re-executed.  To force the shell to perform initialization
1041       and then call the function defined, the file should contain initializa‐
1042       tion code (which will be executed then discarded) in addition to a com‐
1043       plete function definition (which will be retained for subsequent  calls
1044       to the function), and a call to the shell function, including any argu‐
1045       ments, at the end.
1046
1047       For example, suppose the autoload file func contains
1048
1049              func() { print This is func; }
1050              print func is initialized
1051
1052       then `func; func' with KSH_AUTOLOAD set will produce both  messages  on
1053       the  first  call, but only the message `This is func' on the second and
1054       subsequent calls.  Without KSH_AUTOLOAD set, it will produce  the  ini‐
1055       tialization  message  on  the  first call, and the other message on the
1056       second and subsequent calls.
1057
1058       It is also possible to create a function that  is  not  marked  as  au‐
1059       toloaded, but which loads its own definition by searching fpath, by us‐
1060       ing `autoload -X' within a shell function.  For example, the  following
1061       are equivalent:
1062
1063              myfunc() {
1064                autoload -X
1065              }
1066              myfunc args...
1067
1068       and
1069
1070              unfunction myfunc   # if myfunc was defined
1071              autoload myfunc
1072              myfunc args...
1073
1074       In  fact,  the  functions  command outputs `builtin autoload -X' as the
1075       body of an autoloaded function.  This is done so that
1076
1077              eval "$(functions)"
1078
1079       produces a reasonable result.  A true autoloaded function can be  iden‐
1080       tified  by  the  presence of the comment `# undefined' in the body, be‐
1081       cause all comments are discarded from defined functions.
1082
1083       To load the definition of an autoloaded function myfunc without execut‐
1084       ing myfunc, use:
1085
1086              autoload +X myfunc
1087

ANONYMOUS FUNCTIONS

1089       If  no  name  is given for a function, it is `anonymous' and is handled
1090       specially.  Either form of function definition may be used: a `()' with
1091       no  preceding  name, or a `function' with an immediately following open
1092       brace.  The function is executed immediately at the point of definition
1093       and  is  not  stored  for  future  use.   The  function  name is set to
1094       `(anon)'.
1095
1096       Arguments to the function may be specified as words following the clos‐
1097       ing  brace  defining the function, hence if there are none no arguments
1098       (other than $0) are set.  This is a difference from the way other func‐
1099       tions  are  parsed: normal function definitions may be followed by cer‐
1100       tain keywords such as `else' or `fi', which will be  treated  as  argu‐
1101       ments  to anonymous functions, so that a newline or semicolon is needed
1102       to force keyword interpretation.
1103
1104       Note also that the argument list of any enclosing script or function is
1105       hidden  (as  would  be  the  case for any other function called at this
1106       point).
1107
1108       Redirections may be applied to the anonymous function in the same  man‐
1109       ner  as  to a current-shell structure enclosed in braces.  The main use
1110       of anonymous functions is to provide a scope for local variables.  This
1111       is  particularly  convenient  in start-up files as these do not provide
1112       their own local variable scope.
1113
1114       For example,
1115
1116              variable=outside
1117              function {
1118                local variable=inside
1119                print "I am $variable with arguments $*"
1120              } this and that
1121              print "I am $variable"
1122
1123       outputs the following:
1124
1125              I am inside with arguments this and that
1126              I am outside
1127
1128       Note that function definitions with arguments that expand  to  nothing,
1129       for  example `name=; function $name { ... }', are not treated as anony‐
1130       mous functions.  Instead, they are treated as normal  function  defini‐
1131       tions where the definition is silently discarded.
1132

SPECIAL FUNCTIONS

1134       Certain functions, if defined, have special meaning to the shell.
1135
1136   Hook Functions
1137       For the functions below, it is possible to define an array that has the
1138       same name as the function with `_functions' appended.  Any  element  in
1139       such an array is taken as the name of a function to execute; it is exe‐
1140       cuted in the same context and with the same arguments and same  initial
1141       value  of  $?  as the basic function.  For example, if $chpwd_functions
1142       is an array containing  the  values  `mychpwd',  `chpwd_save_dirstack',
1143       then the shell attempts to execute the functions `chpwd', `mychpwd' and
1144       `chpwd_save_dirstack', in that order.  Any function that does not exist
1145       is silently ignored.  A function found by this mechanism is referred to
1146       elsewhere as a hook function.  An error in any function  causes  subse‐
1147       quent  functions not to be run.  Note further that an error in a precmd
1148       hook causes an immediately  following  periodic  function  not  to  run
1149       (though it may run at the next opportunity).
1150
1151       chpwd  Executed whenever the current working directory is changed.
1152
1153       periodic
1154              If  the parameter PERIOD is set, this function is executed every
1155              $PERIOD seconds, just before a prompt.  Note  that  if  multiple
1156              functions  are  defined  using the array periodic_functions only
1157              one period is applied to the complete set of functions, and  the
1158              scheduled time is not reset if the list of functions is altered.
1159              Hence the set of functions is always called together.
1160
1161       precmd Executed before each prompt.  Note that precommand functions are
1162              not  re-executed  simply because the command line is redrawn, as
1163              happens, for example, when a notification about an  exiting  job
1164              is displayed.
1165
1166       preexec
1167              Executed  just  after a command has been read and is about to be
1168              executed.  If the history mechanism  is  active  (regardless  of
1169              whether  the  line  was  discarded from the history buffer), the
1170              string that the user typed is passed as the first argument, oth‐
1171              erwise  it  is an empty string.  The actual command that will be
1172              executed (including expanded aliases) is passed in two different
1173              forms:  the  second argument is a single-line, size-limited ver‐
1174              sion of the command (with things like function  bodies  elided);
1175              the  third  argument  contains  the full text that is being exe‐
1176              cuted.
1177
1178       zshaddhistory
1179              Executed when a history line has been  read  interactively,  but
1180              before  it  is executed.  The sole argument is the complete his‐
1181              tory line  (so  that  any  terminating  newline  will  still  be
1182              present).
1183
1184              If  any  of the hook functions returns status 1 (or any non-zero
1185              value other than 2, though this is  not  guaranteed  for  future
1186              versions  of  the shell) the history line will not be saved, al‐
1187              though it lingers in the history until the  next  line  is  exe‐
1188              cuted, allowing you to reuse or edit it immediately.
1189
1190              If  any  of the hook functions returns status 2 the history line
1191              will be saved on the internal history list, but not  written  to
1192              the  history  file.   In  case of a conflict, the first non-zero
1193              status value is taken.
1194
1195              A hook function may call `fc -p ...' to switch the history  con‐
1196              text  so that the history is saved in a different file from that
1197              in the global HISTFILE parameter.  This  is  handled  specially:
1198              the history context is automatically restored after the process‐
1199              ing of the history line is finished.
1200
1201              The following example function works with  one  of  the  options
1202              INC_APPEND_HISTORY  or SHARE_HISTORY set, in order that the line
1203              is written out immediately after the history entry is added.  It
1204              first  adds the history line to the normal history with the new‐
1205              line stripped, which is usually the correct behaviour.  Then  it
1206              switches the history context so that the line will be written to
1207              a history file in the current directory.
1208
1209                     zshaddhistory() {
1210                       print -sr -- ${1%%$'\n'}
1211                       fc -p .zsh_local_history
1212                     }
1213
1214       zshexit
1215              Executed at the point where the main shell is about to exit nor‐
1216              mally.   This  is  not called by exiting subshells, nor when the
1217              exec precommand modifier is used  before  an  external  command.
1218              Also, unlike TRAPEXIT, it is not called when functions exit.
1219
1220   Trap Functions
1221       The functions below are treated specially but do not have corresponding
1222       hook arrays.
1223
1224       TRAPNAL
1225              If defined and non-null, this function will be executed whenever
1226              the shell catches a signal SIGNAL, where NAL is a signal name as
1227              specified for the kill  builtin.   The  signal  number  will  be
1228              passed as the first parameter to the function.
1229
1230              If  a  function  of this form is defined and null, the shell and
1231              processes spawned by it will ignore SIGNAL.
1232
1233              The return status from the function is handled specially.  If it
1234              is  zero, the signal is assumed to have been handled, and execu‐
1235              tion continues normally.  Otherwise, the shell  will  behave  as
1236              interrupted  except  that  the  return status of the trap is re‐
1237              tained.
1238
1239              Programs terminated by uncaught  signals  typically  return  the
1240              status  128  plus the signal number.  Hence the following causes
1241              the handler for SIGINT to print a message, then mimic the  usual
1242              effect of the signal.
1243
1244                     TRAPINT() {
1245                       print "Caught SIGINT, aborting."
1246                       return $(( 128 + $1 ))
1247                     }
1248
1249              The  functions  TRAPZERR,  TRAPDEBUG and TRAPEXIT are never exe‐
1250              cuted inside other traps.
1251
1252       TRAPDEBUG
1253              If the option DEBUG_BEFORE_CMD is set (as it is by default), ex‐
1254              ecuted  before  each command; otherwise executed after each com‐
1255              mand.  See the description of the trap builtin in zshbuiltins(1)
1256              for details of additional features provided in debug traps.
1257
1258       TRAPEXIT
1259              Executed  when the shell exits, or when the current function ex‐
1260              its if defined inside a function.  The value of $? at the  start
1261              of  execution is the exit status of the shell or the return sta‐
1262              tus of the function exiting.
1263
1264       TRAPZERR
1265              Executed whenever a command has a non-zero  exit  status.   How‐
1266              ever,  the function is not executed if the command occurred in a
1267              sublist followed by `&&' or `||'; only the final  command  in  a
1268              sublist  of this type causes the trap to be executed.  The func‐
1269              tion TRAPERR acts the same as TRAPZERR on systems where there is
1270              no SIGERR (this is the usual case).
1271
1272       The  functions  beginning  `TRAP' may alternatively be defined with the
1273       trap builtin:  this may be preferable for some uses.   Setting  a  trap
1274       with  one  form removes any trap of the other form for the same signal;
1275       removing a trap in either form removes all traps for the  same  signal.
1276       The forms
1277
1278              TRAPNAL() {
1279               # code
1280              }
1281
1282       ('function traps') and
1283
1284              trap '
1285               # code
1286              ' NAL
1287
1288       ('list  traps')  are  equivalent in most ways, the exceptions being the
1289       following:
1290
1291       •      Function traps have all the properties of normal functions,  ap‐
1292              pearing in the list of functions and being called with their own
1293              function context rather than the  context  where  the  trap  was
1294              triggered.
1295
1296       •      The  return status from function traps is special, whereas a re‐
1297              turn from a list trap causes the surrounding context  to  return
1298              with the given status.
1299
1300       •      Function  traps  are  not  reset within subshells, in accordance
1301              with zsh behaviour; list traps are  reset,  in  accordance  with
1302              POSIX behaviour.
1303

JOBS

1305       If  the  MONITOR  option  is set, an interactive shell associates a job
1306       with each pipeline.  It keeps a table of current jobs, printed  by  the
1307       jobs  command,  and  assigns them small integer numbers.  When a job is
1308       started asynchronously with `&', the shell prints a  line  to  standard
1309       error which looks like:
1310
1311              [1] 1234
1312
1313       indicating that the job which was started asynchronously was job number
1314       1 and had one (top-level) process, whose process ID was 1234.
1315
1316       If a job is started with `&|' or `&!', then  that  job  is  immediately
1317       disowned.   After  startup,  it does not have a place in the job table,
1318       and is not subject to the job control features described here.
1319
1320       If you are running a job and wish to do something else you may hit  the
1321       key  ^Z (control-Z) which sends a TSTP signal to the current job:  this
1322       key may be redefined by the susp option of the external  stty  command.
1323       The  shell  will  then  normally  indicate  that the job has been `sus‐
1324       pended', and print another prompt.  You can then manipulate  the  state
1325       of  this  job, putting it in the background with the bg command, or run
1326       some other commands and then eventually bring the  job  back  into  the
1327       foreground  with  the foreground command fg.  A ^Z takes effect immedi‐
1328       ately and is like an interrupt in that pending output and unread  input
1329       are discarded when it is typed.
1330
1331       A job being run in the background will suspend if it tries to read from
1332       the terminal.
1333
1334       Note that if the job running in the foreground  is  a  shell  function,
1335       then  suspending  it will have the effect of causing the shell to fork.
1336       This is necessary to separate the function's state  from  that  of  the
1337       parent  shell performing the job control, so that the latter can return
1338       to the command line prompt.  As a result, even if fg is  used  to  con‐
1339       tinue  the job the function will no longer be part of the parent shell,
1340       and any variables set by the function will not be visible in the parent
1341       shell.   Thus  the behaviour is different from the case where the func‐
1342       tion was never suspended.  Zsh is different from many other  shells  in
1343       this regard.
1344
1345       One  additional side effect is that use of disown with a job created by
1346       suspending shell code in this fashion is delayed: the job can  only  be
1347       disowned once any process started from the parent shell has terminated.
1348       At that point, the disowned job disappears silently from the job list.
1349
1350       The same behaviour is found when the shell is  executing  code  as  the
1351       right  hand  side  of a pipeline or any complex shell construct such as
1352       if, for, etc., in order that the entire block of code can be managed as
1353       a  single job.  Background jobs are normally allowed to produce output,
1354       but this can be disabled by giving the command `stty tostop'.   If  you
1355       set this tty option, then background jobs will suspend when they try to
1356       produce output like they do when they try to read input.
1357
1358       When a command is suspended and continued later with  the  fg  or  wait
1359       builtins,  zsh  restores tty modes that were in effect when it was sus‐
1360       pended.  This (intentionally) does not apply if the command is  contin‐
1361       ued via `kill -CONT', nor when it is continued with bg.
1362
1363       There are several ways to refer to jobs in the shell.  A job can be re‐
1364       ferred to by the process ID of any process of the job or by one of  the
1365       following:
1366
1367       %number
1368              The job with the given number.
1369       %string
1370              The last job whose command line begins with string.
1371       %?string
1372              The last job whose command line contains string.
1373       %%     Current job.
1374       %+     Equivalent to `%%'.
1375       %-     Previous job.
1376
1377       The shell learns immediately whenever a process changes state.  It nor‐
1378       mally informs you whenever a job becomes blocked  so  that  no  further
1379       progress  is possible.  If the NOTIFY option is not set, it waits until
1380       just before it prints a prompt before it informs you.  All such notifi‐
1381       cations  are  sent directly to the terminal, not to the standard output
1382       or standard error.
1383
1384       When the monitor mode is on, each background job that  completes  trig‐
1385       gers any trap set for CHLD.
1386
1387       When  you  try  to leave the shell while jobs are running or suspended,
1388       you will be warned that `You have suspended (running) jobs'.   You  may
1389       use  the  jobs command to see what they are.  If you do this or immedi‐
1390       ately try to exit again, the shell will not warn you a second time; the
1391       suspended  jobs will be terminated, and the running jobs will be sent a
1392       SIGHUP signal, if the HUP option is set.
1393
1394       To avoid having the shell terminate the running jobs,  either  use  the
1395       nohup(1) command or the disown builtin.
1396

SIGNALS

1398       The INT and QUIT signals for an invoked command are ignored if the com‐
1399       mand is followed by `&' and the MONITOR  option  is  not  active.   The
1400       shell  itself  always ignores the QUIT signal.  Otherwise, signals have
1401       the values inherited by the shell from its parent (but see the  TRAPNAL
1402       special functions in the section `Functions').
1403
1404       Certain  jobs  are run asynchronously by the shell other than those ex‐
1405       plicitly put into the background; even in cases where the  shell  would
1406       usually wait for such jobs, an explicit exit command or exit due to the
1407       option ERR_EXIT will cause the shell to exit without waiting.  Examples
1408       of  such  asynchronous  jobs  are process substitution, see the section
1409       PROCESS SUBSTITUTION in the zshexpn(1) manual  page,  and  the  handler
1410       processes for multios, see the section MULTIOS in the zshmisc(1) manual
1411       page.
1412

ARITHMETIC EVALUATION

1414       The shell can perform integer and floating point arithmetic, either us‐
1415       ing  the  builtin let, or via a substitution of the form $((...)).  For
1416       integers, the shell is usually compiled to use 8-byte  precision  where
1417       this is available, otherwise precision is 4 bytes.  This can be tested,
1418       for example, by giving the command `print - $(( 12345678901 ))'; if the
1419       number  appears unchanged, the precision is at least 8 bytes.  Floating
1420       point arithmetic always uses the `double'  type  with  whatever  corre‐
1421       sponding precision is provided by the compiler and the library.
1422
1423       The let builtin command takes arithmetic expressions as arguments; each
1424       is evaluated separately.  Since many of the  arithmetic  operators,  as
1425       well  as  spaces, require quoting, an alternative form is provided: for
1426       any command which begins with a `((', all the characters until a match‐
1427       ing  `))'  are treated as a double-quoted expression and arithmetic ex‐
1428       pansion performed as for an argument of let.  More precisely, `((...))'
1429       is equivalent to `let "..."'.  The return status is 0 if the arithmetic
1430       value of the expression is non-zero, 1 if it is zero, and 2 if an error
1431       occurred.
1432
1433       For example, the following statement
1434
1435              (( val = 2 + 1 ))
1436
1437       is equivalent to
1438
1439              let "val = 2 + 1"
1440
1441       both  assigning  the  value 3 to the shell variable val and returning a
1442       zero status.
1443
1444       Integers can be in bases other than 10.  A leading `0x' or `0X' denotes
1445       hexadecimal and a leading `0b' or `0B' binary.  Integers may also be of
1446       the form `base#n', where base is  a  decimal  number  between  two  and
1447       thirty-six  representing  the arithmetic base and n is a number in that
1448       base (for example, `16#ff' is 255 in hexadecimal).  The base# may  also
1449       be omitted, in which case base 10 is used.  For backwards compatibility
1450       the form `[base]n' is also accepted.
1451
1452       An integer expression or a base given in the form `base#n' may  contain
1453       underscores  (`_')  after  the leading digit for visual guidance; these
1454       are ignored in computation.   Examples  are  1_000_000  or  0xffff_ffff
1455       which are equivalent to 1000000 and 0xffffffff respectively.
1456
1457       It is also possible to specify a base to be used for output in the form
1458       `[#base]', for example `[#16]'.  This is used  when  outputting  arith‐
1459       metical  substitutions  or  when assigning to scalar parameters, but an
1460       explicitly defined integer or floating point parameter will not be  af‐
1461       fected.   If an integer variable is implicitly defined by an arithmetic
1462       expression, any base specified in this way will be  set  as  the  vari‐
1463       able's output arithmetic base as if the option `-i base' to the typeset
1464       builtin had been used.  The expression has no precedence and if it  oc‐
1465       curs  more than once in a mathematical expression, the last encountered
1466       is used.  For clarity it is recommended that it appear at the beginning
1467       of an expression.  As an example:
1468
1469              typeset -i 16 y
1470              print $(( [#8] x = 32, y = 32 ))
1471              print $x $y
1472
1473       outputs first `8#40', the rightmost value in the given output base, and
1474       then `8#40 16#20', because y has been explicitly declared to have  out‐
1475       put base 16, while x (assuming it does not already exist) is implicitly
1476       typed by the arithmetic evaluation, where it acquires the  output  base
1477       8.
1478
1479       The base may be replaced or followed by an underscore, which may itself
1480       be followed by a positive integer (if it is  missing  the  value  3  is
1481       used).   This  indicates  that  underscores should be inserted into the
1482       output string, grouping the number for visual clarity.   The  following
1483       integer specifies the number of digits to group together.  For example:
1484
1485              setopt cbases
1486              print $(( [#16_4] 65536 ** 2 ))
1487
1488       outputs `0x1_0000_0000'.
1489
1490       The  feature can be used with floating point numbers, in which case the
1491       base must be omitted; grouping is away from the decimal point.  For ex‐
1492       ample,
1493
1494              zmodload zsh/mathfunc
1495              print $(( [#_] sqrt(1e7) ))
1496
1497       outputs  `3_162.277_660_168_379_5'  (the number of decimal places shown
1498       may vary).
1499
1500       If the C_BASES option is set, hexadecimal numbers  are  output  in  the
1501       standard C format, for example `0xFF' instead of the usual `16#FF'.  If
1502       the option OCTAL_ZEROES is also set (it is not by default), octal  num‐
1503       bers  will  be  treated  similarly and hence appear as `077' instead of
1504       `8#77'.  This option has no effect on the output of  bases  other  than
1505       hexadecimal  and  octal, and these formats are always understood on in‐
1506       put.
1507
1508       When an output base is specified using the `[#base]' syntax, an  appro‐
1509       priate  base prefix will be output if necessary, so that the value out‐
1510       put is valid syntax for input.   If  the  #  is  doubled,  for  example
1511       `[##16]', then no base prefix is output.
1512
1513       Floating  point  constants  are recognized by the presence of a decimal
1514       point or an exponent.  The decimal point may be the first character  of
1515       the  constant, but the exponent character e or E may not, as it will be
1516       taken for a parameter name.  All numeric parts (before  and  after  the
1517       decimal  point  and  in the exponent) may contain underscores after the
1518       leading digit for visual guidance; these are ignored in computation.
1519
1520       An arithmetic expression uses nearly the same syntax and  associativity
1521       of expressions as in C.
1522
1523       In  the native mode of operation, the following operators are supported
1524       (listed in decreasing order of precedence):
1525
1526       + - ! ~ ++ --
1527              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1528              ment
1529       << >>  bitwise shift left, right
1530       &      bitwise AND
1531       ^      bitwise XOR
1532       |      bitwise OR
1533       **     exponentiation
1534       * / %  multiplication, division, modulus (remainder)
1535       + -    addition, subtraction
1536       < > <= >=
1537              comparison
1538       == !=  equality and inequality
1539       &&     logical AND
1540       || ^^  logical OR, XOR
1541       ? :    ternary operator
1542       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1543              assignment
1544       ,      comma operator
1545
1546       The  operators  `&&',  `||', `&&=', and `||=' are short-circuiting, and
1547       only one of the latter two expressions in a ternary operator is  evalu‐
1548       ated.  Note the precedence of the bitwise AND, OR, and XOR operators.
1549
1550       With the option C_PRECEDENCES the precedences (but no other properties)
1551       of the operators are altered to be the same as those in most other lan‐
1552       guages that support the relevant operators:
1553
1554       + - ! ~ ++ --
1555              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1556              ment
1557       **     exponentiation
1558       * / %  multiplication, division, modulus (remainder)
1559       + -    addition, subtraction
1560       << >>  bitwise shift left, right
1561       < > <= >=
1562              comparison
1563       == !=  equality and inequality
1564       &      bitwise AND
1565       ^      bitwise XOR
1566       |      bitwise OR
1567       &&     logical AND
1568       ^^     logical XOR
1569       ||     logical OR
1570       ? :    ternary operator
1571       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1572              assignment
1573       ,      comma operator
1574
1575       Note the precedence of exponentiation in both cases is  below  that  of
1576       unary  operators, hence `-3**2' evaluates as `9', not `-9'.  Use paren‐
1577       theses where necessary: `-(3**2)'.   This  is  for  compatibility  with
1578       other shells.
1579
1580       Mathematical  functions  can  be  called  with the syntax `func(args)',
1581       where the function decides if the  args  is  used  as  a  string  or  a
1582       comma-separated list of arithmetic expressions. The shell currently de‐
1583       fines no mathematical functions by default, but the module zsh/mathfunc
1584       may  be  loaded  with the zmodload builtin to provide standard floating
1585       point mathematical functions.
1586
1587       An expression of the form `##x' where x is any character sequence  such
1588       as `a', `^A', or `\M-\C-x' gives the value of this character and an ex‐
1589       pression of the form `#name' gives the value of the first character  of
1590       the  contents of the parameter name.  Character values are according to
1591       the character set used in the current locale; for  multibyte  character
1592       handling the option MULTIBYTE must be set.  Note that this form is dif‐
1593       ferent from `$#name', a standard parameter substitution which gives the
1594       length  of  the  parameter name.  `#\' is accepted instead of `##', but
1595       its use is deprecated.
1596
1597       Named parameters and subscripted  arrays  can  be  referenced  by  name
1598       within  an  arithmetic expression without using the parameter expansion
1599       syntax.  For example,
1600
1601              ((val2 = val1 * 2))
1602
1603       assigns twice the value of $val1 to the parameter named val2.
1604
1605       An internal integer representation of a named parameter can  be  speci‐
1606       fied  with  the integer builtin.  Arithmetic evaluation is performed on
1607       the value of each assignment to a named parameter declared  integer  in
1608       this  manner.   Assigning a floating point number to an integer results
1609       in rounding towards zero.
1610
1611       Likewise, floating  point  numbers  can  be  declared  with  the  float
1612       builtin; there are two types, differing only in their output format, as
1613       described for the typeset builtin.  The output format can  be  bypassed
1614       by using arithmetic substitution instead of the parameter substitution,
1615       i.e. `${float}' uses  the  defined  format,  but  `$((float))'  uses  a
1616       generic floating point format.
1617
1618       Promotion of integer to floating point values is performed where neces‐
1619       sary.  In addition, if any operator which  requires  an  integer  (`&',
1620       `|',  `^', `<<', `>>' and their equivalents with assignment) is given a
1621       floating point argument, it will be silently rounded towards  zero  ex‐
1622       cept for `~' which rounds down.
1623
1624       Users  should  beware  that, in common with many other programming lan‐
1625       guages but not software designed for calculation, the evaluation of  an
1626       expression  in  zsh is taken a term at a time and promotion of integers
1627       to floating point does not occur in terms only containing integers.   A
1628       typical  result of this is that a division such as 6/8 is truncated, in
1629       this being rounded towards 0.  The FORCE_FLOAT shell option can be used
1630       in  scripts  or  functions  where floating point evaluation is required
1631       throughout.
1632
1633       Scalar variables can hold integer or floating point values at different
1634       times; there is no memory of the numeric type in this case.
1635
1636       If a variable is first assigned in a numeric context without previously
1637       being declared, it will be implicitly typed as integer or float and re‐
1638       tain that type either until the type is explicitly changed or until the
1639       end of the scope.  This can have unforeseen consequences.  For example,
1640       in the loop
1641
1642              for (( f = 0; f < 1; f += 0.1 )); do
1643              # use $f
1644              done
1645
1646       if  f has not already been declared, the first assignment will cause it
1647       to be created as an integer, and consequently the operation `f +=  0.1'
1648       will  always cause the result to be truncated to zero, so that the loop
1649       will fail.  A simple fix would be to turn the initialization into `f  =
1650       0.0'.   It is therefore best to declare numeric variables with explicit
1651       types.
1652

CONDITIONAL EXPRESSIONS

1654       A conditional expression is used with the [[ compound command  to  test
1655       attributes  of  files  and  to compare strings.  Each expression can be
1656       constructed from one or more of the following unary or  binary  expres‐
1657       sions:
1658
1659       -a file
1660              true if file exists.
1661
1662       -b file
1663              true if file exists and is a block special file.
1664
1665       -c file
1666              true if file exists and is a character special file.
1667
1668       -d file
1669              true if file exists and is a directory.
1670
1671       -e file
1672              true if file exists.
1673
1674       -f file
1675              true if file exists and is a regular file.
1676
1677       -g file
1678              true if file exists and has its setgid bit set.
1679
1680       -h file
1681              true if file exists and is a symbolic link.
1682
1683       -k file
1684              true if file exists and has its sticky bit set.
1685
1686       -n string
1687              true if length of string is non-zero.
1688
1689       -o option
1690              true if option named option is on.  option may be a single char‐
1691              acter, in which case it is a single letter  option  name.   (See
1692              the section `Specifying Options'.)
1693
1694              When  no  option named option exists, and the POSIX_BUILTINS op‐
1695              tion hasn't been set, return 3 with a warning.  If  that  option
1696              is set, return 1 with no warning.
1697
1698       -p file
1699              true if file exists and is a FIFO special file (named pipe).
1700
1701       -r file
1702              true if file exists and is readable by current process.
1703
1704       -s file
1705              true if file exists and has size greater than zero.
1706
1707       -t fd  true  if file descriptor number fd is open and associated with a
1708              terminal device.  (note: fd is not optional)
1709
1710       -u file
1711              true if file exists and has its setuid bit set.
1712
1713       -v varname
1714              true if shell variable varname is set.
1715
1716       -w file
1717              true if file exists and is writable by current process.
1718
1719       -x file
1720              true if file exists and is executable by  current  process.   If
1721              file  exists  and  is  a directory, then the current process has
1722              permission to search in the directory.
1723
1724       -z string
1725              true if length of string is zero.
1726
1727       -L file
1728              true if file exists and is a symbolic link.
1729
1730       -O file
1731              true if file exists and is owned by the  effective  user  ID  of
1732              this process.
1733
1734       -G file
1735              true if file exists and its group matches the effective group ID
1736              of this process.
1737
1738       -S file
1739              true if file exists and is a socket.
1740
1741       -N file
1742              true if file exists and its access time is not  newer  than  its
1743              modification time.
1744
1745       file1 -nt file2
1746              true if file1 exists and is newer than file2.
1747
1748       file1 -ot file2
1749              true if file1 exists and is older than file2.
1750
1751       file1 -ef file2
1752              true if file1 and file2 exist and refer to the same file.
1753
1754       string = pattern
1755       string == pattern
1756              true  if  string  matches  pattern.   The  two forms are exactly
1757              equivalent.  The `=' form is the traditional shell  syntax  (and
1758              hence the only one generally used with the test and [ builtins);
1759              the `==' form provides compatibility with other  sorts  of  com‐
1760              puter language.
1761
1762       string != pattern
1763              true if string does not match pattern.
1764
1765       string =~ regexp
1766              true  if  string  matches the regular expression regexp.  If the
1767              option RE_MATCH_PCRE is set regexp is tested as a  PCRE  regular
1768              expression  using  the  zsh/pcre  module, else it is tested as a
1769              POSIX extended regular expression using  the  zsh/regex  module.
1770              Upon  successful match, some variables will be updated; no vari‐
1771              ables are changed if the matching fails.
1772
1773              If the option BASH_REMATCH is not set the scalar parameter MATCH
1774              is set to the substring that matched the pattern and the integer
1775              parameters MBEGIN and MEND to the index of the  start  and  end,
1776              respectively,  of  the  match  in string, such that if string is
1777              contained in variable var the expression `${var[$MBEGIN,$MEND]}'
1778              is  identical to `$MATCH'.  The setting of the option KSH_ARRAYS
1779              is respected.  Likewise, the array match  is  set  to  the  sub‐
1780              strings that matched parenthesised subexpressions and the arrays
1781              mbegin and mend to the indices of the start and  end  positions,
1782              respectively,  of  the substrings within string.  The arrays are
1783              not set if there were no parenthesised subexpressions.  For  ex‐
1784              ample,  if  the  string  `a short string' is matched against the
1785              regular expression `s(...)t', then (assuming the option  KSH_AR‐
1786              RAYS  is  not  set) MATCH, MBEGIN and MEND are `short', 3 and 7,
1787              respectively, while match, mbegin and mend are single entry  ar‐
1788              rays containing the strings `hor', `4' and `6', respectively.
1789
1790              If  the option BASH_REMATCH is set the array BASH_REMATCH is set
1791              to the substring that matched the pattern followed by  the  sub‐
1792              strings  that  matched  parenthesised  subexpressions within the
1793              pattern.
1794
1795       string1 < string2
1796              true if string1 comes before string2 based  on  ASCII  value  of
1797              their characters.
1798
1799       string1 > string2
1800              true  if  string1  comes  after  string2 based on ASCII value of
1801              their characters.
1802
1803       exp1 -eq exp2
1804              true if exp1 is numerically equal to exp2.  Note that for purely
1805              numeric  comparisons use of the ((...)) builtin described in the
1806              section `ARITHMETIC EVALUATION' is more convenient  than  condi‐
1807              tional expressions.
1808
1809       exp1 -ne exp2
1810              true if exp1 is numerically not equal to exp2.
1811
1812       exp1 -lt exp2
1813              true if exp1 is numerically less than exp2.
1814
1815       exp1 -gt exp2
1816              true if exp1 is numerically greater than exp2.
1817
1818       exp1 -le exp2
1819              true if exp1 is numerically less than or equal to exp2.
1820
1821       exp1 -ge exp2
1822              true if exp1 is numerically greater than or equal to exp2.
1823
1824       ( exp )
1825              true if exp is true.
1826
1827       ! exp  true if exp is false.
1828
1829       exp1 && exp2
1830              true if exp1 and exp2 are both true.
1831
1832       exp1 || exp2
1833              true if either exp1 or exp2 is true.
1834
1835       For  compatibility, if there is a single argument that is not syntacti‐
1836       cally significant, typically a variable, the condition is treated as  a
1837       test for whether the expression expands as a string of non-zero length.
1838       In other words, [[ $var ]] is the same as [[ -n $var ]].  It is  recom‐
1839       mended that the second, explicit, form be used where possible.
1840
1841       Normal shell expansion is performed on the file, string and pattern ar‐
1842       guments, but the result of each expansion is constrained to be a single
1843       word, similar to the effect of double quotes.
1844
1845       Filename  generation is not performed on any form of argument to condi‐
1846       tions.  However, it can be forced in any case where normal shell expan‐
1847       sion  is  valid and when the option EXTENDED_GLOB is in effect by using
1848       an explicit glob qualifier of the form (#q) at the end of  the  string.
1849       A  normal  glob qualifier expression may appear between the `q' and the
1850       closing parenthesis; if none appears the expression has no  effect  be‐
1851       yond  causing  filename generation.  The results of filename generation
1852       are joined together to form a single word, as with the results of other
1853       forms of expansion.
1854
1855       This  special  use of filename generation is only available with the [[
1856       syntax.  If the condition occurs within the [ or test builtin  commands
1857       then  globbing  occurs instead as part of normal command line expansion
1858       before the condition is evaluated.  In this case it may generate multi‐
1859       ple words which are likely to confuse the syntax of the test command.
1860
1861       For example,
1862
1863              [[ -n file*(#qN) ]]
1864
1865       produces  status  zero if and only if there is at least one file in the
1866       current directory beginning with the string `file'.  The globbing qual‐
1867       ifier  N  ensures  that the expression is empty if there is no matching
1868       file.
1869
1870       Pattern metacharacters are active for the pattern arguments;  the  pat‐
1871       terns  are  the  same  as  those used for filename generation, see zsh‐
1872       expn(1), but there is no special behaviour of `/' nor initial dots, and
1873       no glob qualifiers are allowed.
1874
1875       In  each  of the above expressions, if file is of the form `/dev/fd/n',
1876       where n is an integer, then the test applied to the open file whose de‐
1877       scriptor  number  is  n, even if the underlying system does not support
1878       the /dev/fd directory.
1879
1880       In the forms which do numeric comparison, the expressions  exp  undergo
1881       arithmetic expansion as if they were enclosed in $((...)).
1882
1883       For example, the following:
1884
1885              [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
1886
1887       tests if either file foo or file bar exists, and if so, if the value of
1888       the parameter report begins with `y';  if  the  complete  condition  is
1889       true, the message `File exists.' is printed.
1890

EXPANSION OF PROMPT SEQUENCES

1892       Prompt sequences undergo a special form of expansion.  This type of ex‐
1893       pansion is also available using the -P option to the print builtin.
1894
1895       If the PROMPT_SUBST option is set, the prompt string is first subjected
1896       to  parameter expansion, command substitution and arithmetic expansion.
1897       See zshexpn(1).
1898
1899       Certain escape sequences may be recognised in the prompt string.
1900
1901       If the PROMPT_BANG option is set, a `!' in the prompt  is  replaced  by
1902       the  current  history  event  number.  A literal `!' may then be repre‐
1903       sented as `!!'.
1904
1905       If the PROMPT_PERCENT option is  set,  certain  escape  sequences  that
1906       start  with  `%'  are  expanded.  Many escapes are followed by a single
1907       character, although some of these take  an  optional  integer  argument
1908       that  should  appear  between the `%' and the next character of the se‐
1909       quence.  More complicated escape sequences  are  available  to  provide
1910       conditional expansion.
1911

SIMPLE PROMPT ESCAPES

1913   Special characters
1914       %%     A `%'.
1915
1916       %)     A `)'.
1917
1918   Login information
1919       %l     The line (tty) the user is logged in on, without `/dev/' prefix.
1920              If the name starts with `/dev/tty', that prefix is stripped.
1921
1922       %M     The full machine hostname.
1923
1924       %m     The hostname up to the first `.'.  An integer may follow the `%'
1925              to  specify  how  many  components  of the hostname are desired.
1926              With a negative integer, trailing components of the hostname are
1927              shown.
1928
1929       %n     $USERNAME.
1930
1931       %y     The line (tty) the user is logged in on, without `/dev/' prefix.
1932              This does not treat `/dev/tty' names specially.
1933
1934   Shell state
1935       %#     A `#' if the shell is running with privileges,  a  `%'  if  not.
1936              Equivalent  to `%(!.#.%%)'.  The definition of `privileged', for
1937              these purposes, is that either the effective user  ID  is  zero,
1938              or,  if  POSIX.1e  capabilities are supported, that at least one
1939              capability is raised in either the Effective or Inheritable  ca‐
1940              pability vectors.
1941
1942       %?     The  return  status of the last command executed just before the
1943              prompt.
1944
1945       %_     The status of the parser, i.e. the shell constructs  (like  `if'
1946              and  `for') that have been started on the command line. If given
1947              an integer number that many strings will  be  printed;  zero  or
1948              negative  or  no integer means print as many as there are.  This
1949              is most useful in prompts PS2 for continuation lines and PS4 for
1950              debugging  with  the  XTRACE  option; in the latter case it will
1951              also work non-interactively.
1952
1953       %^     The status of the parser in reverse. This is the  same  as  `%_'
1954              other than the order of strings.  It is often used in RPS2.
1955
1956       %d
1957       %/     Current  working  directory.   If an integer follows the `%', it
1958              specifies a number of trailing components of the current working
1959              directory  to show; zero means the whole path.  A negative inte‐
1960              ger specifies leading components, i.e. %-1d specifies the  first
1961              component.
1962
1963       %~     As  %d  and %/, but if the current working directory starts with
1964              $HOME, that part is replaced by a `~'. Furthermore, if it has  a
1965              named  directory  as  its prefix, that part is replaced by a `~'
1966              followed by the name of the directory, but only if the result is
1967              shorter  than the full path; see Dynamic and Static named direc‐
1968              tories in zshexpn(1).
1969
1970       %e     Evaluation depth of the current sourced file, shell function, or
1971              eval.   This  is incremented or decremented every time the value
1972              of %N is set or reverted  to  a  previous  value,  respectively.
1973              This is most useful for debugging as part of $PS4.
1974
1975       %h
1976       %!     Current history event number.
1977
1978       %i     The  line number currently being executed in the script, sourced
1979              file, or shell function given by %N.  This is  most  useful  for
1980              debugging as part of $PS4.
1981
1982       %I     The  line  number currently being executed in the file %x.  This
1983              is similar to %i, but the line number is always a line number in
1984              the file where the code was defined, even if the code is a shell
1985              function.
1986
1987       %j     The number of jobs.
1988
1989       %L     The current value of $SHLVL.
1990
1991       %N     The name of the script, sourced file, or shell function that zsh
1992              is currently executing, whichever was started most recently.  If
1993              there is none, this is equivalent to the parameter $0.  An inte‐
1994              ger may follow the `%' to specify a number of trailing path com‐
1995              ponents to show; zero means the full path.  A  negative  integer
1996              specifies leading components.
1997
1998       %x     The  name of the file containing the source code currently being
1999              executed.  This behaves as %N except that function and eval com‐
2000              mand  names  are not shown, instead the file where they were de‐
2001              fined.
2002
2003       %c
2004       %.
2005       %C     Trailing component of the current working directory.  An integer
2006              may  follow the `%' to get more than one component.  Unless `%C'
2007              is used, tilde contraction is performed first.  These are depre‐
2008              cated  as %c and %C are equivalent to %1~ and %1/, respectively,
2009              while explicit positive integers have the same effect as for the
2010              latter two sequences.
2011
2012   Date and time
2013       %D     The date in yy-mm-dd format.
2014
2015       %T     Current time of day, in 24-hour format.
2016
2017       %t
2018       %@     Current time of day, in 12-hour, am/pm format.
2019
2020       %*     Current time of day in 24-hour format, with seconds.
2021
2022       %w     The date in day-dd format.
2023
2024       %W     The date in mm/dd/yy format.
2025
2026       %D{string}
2027              string  is  formatted  using  the  strftime function.  See strf‐
2028              time(3) for more details.  Various zsh extensions  provide  num‐
2029              bers  with  no  leading  zero or space if the number is a single
2030              digit:
2031
2032              %f     a day of the month
2033              %K     the hour of the day on the 24-hour clock
2034              %L     the hour of the day on the 12-hour clock
2035
2036              In addition, if the system supports the POSIX gettimeofday  sys‐
2037              tem  call,  %.  provides decimal fractions of a second since the
2038              epoch with leading zeroes.  By default three decimal places  are
2039              provided,  but a number of digits up to 9 may be given following
2040              the %; hence %6.  outputs microseconds, and %9. outputs nanosec‐
2041              onds.   (The  latter  requires a nanosecond-precision clock_get‐
2042              time; systems lacking this will return a value multiplied by the
2043              appropriate power of 10.)  A typical example of this is the for‐
2044              mat `%D{%H:%M:%S.%.}'.
2045
2046              The GNU extension %N is handled as a synonym for %9..
2047
2048              Additionally, the GNU extension that a `-' between the % and the
2049              format  character  causes a leading zero or space to be stripped
2050              is handled directly by the shell for the format characters d, f,
2051              H, k, l, m, M, S and y; any other format characters are provided
2052              to the system's strftime(3) with any leading `-' present, so the
2053              handling is system dependent.  Further GNU (or other) extensions
2054              are also passed to strftime(3) and may work if the  system  sup‐
2055              ports them.
2056
2057   Visual effects
2058       %B (%b)
2059              Start (stop) boldface mode.
2060
2061       %E     Clear to end of line.
2062
2063       %U (%u)
2064              Start (stop) underline mode.
2065
2066       %S (%s)
2067              Start (stop) standout mode.
2068
2069       %F (%f)
2070              Start  (stop)  using a different foreground colour, if supported
2071              by the terminal.  The colour may be specified two  ways:  either
2072              as  a  numeric  argument,  as normal, or by a sequence in braces
2073              following the %F, for example %F{red}.  In the latter  case  the
2074              values  allowed are as described for the fg zle_highlight attri‐
2075              bute; see Character Highlighting in zshzle(1).  This means  that
2076              numeric colours are allowed in the second format also.
2077
2078       %K (%k)
2079              Start (stop) using a different bacKground colour.  The syntax is
2080              identical to that for %F and %f.
2081
2082       %{...%}
2083              Include a string as  a  literal  escape  sequence.   The  string
2084              within  the braces should not change the cursor position.  Brace
2085              pairs can nest.
2086
2087              A positive numeric argument between the % and the {  is  treated
2088              as described for %G below.
2089
2090       %G     Within  a  %{...%} sequence, include a `glitch': that is, assume
2091              that a single character width will be output.   This  is  useful
2092              when  outputting  characters  that otherwise cannot be correctly
2093              handled by the shell, such as the  alternate  character  set  on
2094              some  terminals.   The  characters  in  question can be included
2095              within a %{...%} sequence together with the  appropriate  number
2096              of  %G  sequences to indicate the correct width.  An integer be‐
2097              tween the `%' and `G' indicates a  character  width  other  than
2098              one.   Hence  %{seq%2G%} outputs seq and assumes it takes up the
2099              width of two standard characters.
2100
2101              Multiple uses of %G accumulate in the obvious fashion; the posi‐
2102              tion  of  the %G is unimportant.  Negative integers are not han‐
2103              dled.
2104
2105              Note that when prompt truncation is in use it  is  advisable  to
2106              divide  up  output  into  single  characters within each %{...%}
2107              group so that the correct truncation point can be found.
2108

CONDITIONAL SUBSTRINGS IN PROMPTS

2110       %v     The value of the first element of  the  psvar  array  parameter.
2111              Following  the `%' with an integer gives that element of the ar‐
2112              ray.  Negative integers count from the end of the array.
2113
2114       %(x.true-text.false-text)
2115              Specifies a ternary expression.  The character following  the  x
2116              is  arbitrary;  the  same character is used to separate the text
2117              for the `true' result from that for the  `false'  result.   This
2118              separator  may  not appear in the true-text, except as part of a
2119              %-escape sequence.  A `)' may appear in the false-text as  `%)'.
2120              true-text and false-text may both contain arbitrarily-nested es‐
2121              cape sequences, including further ternary expressions.
2122
2123              The left parenthesis may be preceded or followed by  a  positive
2124              integer  n,  which defaults to zero.  A negative integer will be
2125              multiplied by -1, except as noted below for `l'.  The test char‐
2126              acter x may be any of the following:
2127
2128              !      True if the shell is running with privileges.
2129              #      True if the effective uid of the current process is n.
2130              ?      True if the exit status of the last command was n.
2131              _      True if at least n shell constructs were started.
2132              C
2133              /      True if the current absolute path has at least n elements
2134                     relative to the root directory, hence / is counted  as  0
2135                     elements.
2136              c
2137              .
2138              ~      True if the current path, with prefix replacement, has at
2139                     least n elements relative to the root directory, hence  /
2140                     is counted as 0 elements.
2141              D      True if the month is equal to n (January = 0).
2142              d      True if the day of the month is equal to n.
2143              e      True if the evaluation depth is at least n.
2144              g      True if the effective gid of the current process is n.
2145              j      True if the number of jobs is at least n.
2146              L      True if the SHLVL parameter is at least n.
2147              l      True  if  at least n characters have already been printed
2148                     on the current line.  When n  is  negative,  true  if  at
2149                     least abs(n) characters remain before the opposite margin
2150                     (thus the left margin for RPROMPT).
2151              S      True if the SECONDS parameter is at least n.
2152              T      True if the time in hours is equal to n.
2153              t      True if the time in minutes is equal to n.
2154              v      True if the array psvar has at least n elements.
2155              V      True  if  element  n  of  the  array  psvar  is  set  and
2156                     non-empty.
2157              w      True if the day of the week is equal to n (Sunday = 0).
2158
2159       %<string<
2160       %>string>
2161       %[xstring]
2162              Specifies  truncation  behaviour for the remainder of the prompt
2163              string.   The  third,  deprecated,   form   is   equivalent   to
2164              `%xstringx',  i.e. x may be `<' or `>'.  The string will be dis‐
2165              played in place of the truncated portion  of  any  string;  note
2166              this does not undergo prompt expansion.
2167
2168              The numeric argument, which in the third form may appear immedi‐
2169              ately after the `[', specifies the maximum permitted  length  of
2170              the various strings that can be displayed in the prompt.  In the
2171              first two forms, this numeric argument may be negative, in which
2172              case  the truncation length is determined by subtracting the ab‐
2173              solute value of the numeric argument from the number of  charac‐
2174              ter positions remaining on the current prompt line.  If this re‐
2175              sults in a zero or negative length, a length of 1 is  used.   In
2176              other  words, a negative argument arranges that after truncation
2177              at least n characters remain before the right margin (left  mar‐
2178              gin for RPROMPT).
2179
2180              The  forms  with `<' truncate at the left of the string, and the
2181              forms with `>' truncate at the right of the string.   For  exam‐
2182              ple,  if  the  current  directory  is  `/home/pike',  the prompt
2183              `%8<..<%/' will expand to `..e/pike'.  In this string, the  ter‐
2184              minating  character (`<', `>' or `]'), or in fact any character,
2185              may be quoted by a preceding `\'; note when using print -P, how‐
2186              ever, that this must be doubled as the string is also subject to
2187              standard print processing, in addition to  any  backslashes  re‐
2188              moved  by  a  double quoted string:  the worst case is therefore
2189              `print -P "%<\\\\<<..."'.
2190
2191              If the string is longer than the specified truncation length, it
2192              will appear in full, completely replacing the truncated string.
2193
2194              The part of the prompt string to be truncated runs to the end of
2195              the string, or to the end of the next  enclosing  group  of  the
2196              `%('  construct,  or  to  the next truncation encountered at the
2197              same grouping level (i.e. truncations inside a  `%('  are  sepa‐
2198              rate), which ever comes first.  In particular, a truncation with
2199              argument zero (e.g., `%<<') marks the end of the  range  of  the
2200              string  to  be truncated while turning off truncation from there
2201              on. For example, the prompt  `%10<...<%~%<<%#  '  will  print  a
2202              truncated representation of the current directory, followed by a
2203              `%' or `#', followed by a space.  Without the `%<<',  those  two
2204              characters  would  be  included  in  the string to be truncated.
2205              Note that `%-0<<' is not equivalent to `%<<' but specifies  that
2206              the prompt is truncated at the right margin.
2207
2208              Truncation  applies  only  within  each  individual  line of the
2209              prompt, as delimited by embedded newlines (if any).  If the  to‐
2210              tal length of any line of the prompt after truncation is greater
2211              than the terminal width, or if the part to be truncated contains
2212              embedded  newlines,  truncation  behavior  is  undefined and may
2213              change   in   a   future   version   of    the    shell.     Use
2214              `%-n(l.true-text.false-text)' to remove parts of the prompt when
2215              the available space is less than n.
2216
2217
2218
2219zsh 5.9                          May 14, 2022                       ZSHMISC(1)
Impressum