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.
227
228       { list }
229              Execute list.
230
231       { try-list } always { always-list }
232              First  execute try-list.  Regardless of errors, or break or con‐
233              tinue commands encountered within try-list, execute always-list.
234              Execution  then  continues  from  the result of the execution of
235              try-list; in other words, any error, or break or  continue  com‐
236              mand  is  treated  in the normal way, as if always-list were not
237              present.  The two chunks of code are referred  to  as  the  `try
238              block' and the `always block'.
239
240              Optional  newlines  or  semicolons  may appear after the always;
241              note, however, that they may not appear  between  the  preceding
242              closing brace and the always.
243
244              An `error' in this context is a condition such as a syntax error
245              which causes the shell to abort execution of the  current  func‐
246              tion,  script,  or  list.   Syntax  errors encountered while the
247              shell is parsing the code do not cause the always-list to be ex‐
248              ecuted.   For  example,  an  erroneously constructed if block in
249              try-list would cause the shell to abort during parsing, so  that
250              always-list  would not be executed, while an erroneous substitu‐
251              tion such as ${*foo*} would cause a run-time error, after  which
252              always-list would be executed.
253
254              An  error condition can be tested and reset with the special in‐
255              teger variable  TRY_BLOCK_ERROR.   Outside  an  always-list  the
256              value  is  irrelevant,  but it is initialised to -1.  Inside al‐
257              ways-list, the value is 1 if an error occurred in the  try-list,
258              else  0.  If TRY_BLOCK_ERROR is set to 0 during the always-list,
259              the error condition caused by the try-list is reset,  and  shell
260              execution  continues normally after the end of always-list.  Al‐
261              tering the value during the try-list is not useful (unless  this
262              forms part of an enclosing always block).
263
264              Regardless  of TRY_BLOCK_ERROR, after the end of always-list the
265              normal shell status $? is  the  value  returned  from  try-list.
266              This   will   be  non-zero  if  there  was  an  error,  even  if
267              TRY_BLOCK_ERROR was set to zero.
268
269              The following executes the given code, ignoring  any  errors  it
270              causes.   This is an alternative to the usual convention of pro‐
271              tecting code by executing it in a subshell.
272
273                     {
274                         # code which may cause an error
275                       } always {
276                         # This code is executed regardless of the error.
277                         (( TRY_BLOCK_ERROR = 0 ))
278                     }
279                     # The error condition has been reset.
280
281              When a try block occurs outside of any function, a return  or  a
282              exit encountered in try-list does not cause the execution of al‐
283              ways-list.  Instead, the shell exits immediately after any  EXIT
284              trap has been executed.  Otherwise, a return command encountered
285              in try-list will cause the execution of always-list,  just  like
286              break and continue.
287
288       function word ... [ () ] [ term ] { list }
289       word ... () [ term ] { list }
290       word ... () [ term ] command
291              where term is one or more newline or ;.  Define a function which
292              is referenced by any one of word.  Normally, only  one  word  is
293              provided;  multiple  words  are  usually only useful for setting
294              traps.  The body of the function is the list between the  {  and
295              }.  See the section `Functions'.
296
297              If  the  option  SH_GLOB  is  set  for  compatibility with other
298              shells, then whitespace may appear between the  left  and  right
299              parentheses  when there is a single word;  otherwise, the paren‐
300              theses will be treated as forming a  globbing  pattern  in  that
301              case.
302
303              In  any of the forms above, a redirection may appear outside the
304              function body, for example
305
306                     func() { ... } 2>&1
307
308              The redirection is stored with the function and applied whenever
309              the  function is executed.  Any variables in the redirection are
310              expanded at the point the function is executed, but outside  the
311              function scope.
312
313       time [ pipeline ]
314              The  pipeline is executed, and timing statistics are reported on
315              the standard error in the form specified by the TIMEFMT  parame‐
316              ter.   If  pipeline is omitted, print statistics about the shell
317              process and its children.
318
319       [[ exp ]]
320              Evaluates the conditional expression exp and return a zero  exit
321              status if it is true.  See the section `Conditional Expressions'
322              for a description of exp.
323

ALTERNATE FORMS FOR COMPLEX COMMANDS

325       Many of  zsh's  complex  commands  have  alternate  forms.   These  are
326       non-standard  and  are  likely not to be obvious even to seasoned shell
327       programmers; they should not be used anywhere that portability of shell
328       code is a concern.
329
330       The short versions below only work if sublist is of the form `{ list }'
331       or if the SHORT_LOOPS option is set.  For the if, while and until  com‐
332       mands, in both these cases the test part of the loop must also be suit‐
333       ably delimited, such as by `[[ ... ]]' or `(( ... ))', else the end  of
334       the  test will not be recognized.  For the for, repeat, case and select
335       commands no such special form for the arguments is necessary,  but  the
336       other  condition (the special form of sublist or use of the SHORT_LOOPS
337       option) still applies.
338
339       if list { list } [ elif list { list } ] ... [ else { list } ]
340              An alternate form of if.  The rules mean that
341
342                     if [[ -o ignorebraces ]] {
343                       print yes
344                     }
345
346              works, but
347
348                     if true {  # Does not work!
349                       print yes
350                     }
351
352              does not, since the test is not suitably delimited.
353
354       if list sublist
355              A short form of the alternate if.  The same limitations  on  the
356              form of list apply as for the previous form.
357
358       for name ... ( word ... ) sublist
359              A short form of for.
360
361       for name ... [ in word ... ] term sublist
362              where  term is at least one newline or ;.  Another short form of
363              for.
364
365       for (( [expr1] ; [expr2] ; [expr3] )) sublist
366              A short form of the arithmetic for command.
367
368       foreach name ... ( word ... ) list end
369              Another form of for.
370
371       while list { list }
372              An alternative form of while.  Note the limitations on the  form
373              of list mentioned above.
374
375       until list { list }
376              An  alternative form of until.  Note the limitations on the form
377              of list mentioned above.
378
379       repeat word sublist
380              This is a short form of repeat.
381
382       case word { [ [(] pattern [ | pattern ] ... ) list (;;|;&|;|) ] ... }
383              An alternative form of case.
384
385       select name [ in word ... term ] sublist
386              where term is at least one newline or ;.  A short  form  of  se‐
387              lect.
388
389       function word ... [ () ] [ term ] sublist
390              This is a short form of function.
391

RESERVED WORDS

393       The  following  words are recognized as reserved words when used as the
394       first word of a command unless quoted or disabled using disable -r:
395
396       do done esac then elif else fi for case if while function  repeat  time
397       until select coproc nocorrect foreach end ! [[ { } declare export float
398       integer local readonly typeset
399
400       Additionally, `}' is recognized in any  position  if  neither  the  IG‐
401       NORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.
402

ERRORS

404       Certain  errors  are  treated  as fatal by the shell: in an interactive
405       shell, they cause control to return to  the  command  line,  and  in  a
406       non-interactive  shell  they  cause  the shell to be aborted.  In older
407       versions of zsh, a non-interactive shell running  a  script  would  not
408       abort  completely, but would resume execution at the next command to be
409       read from the script, skipping the remainder of any functions or  shell
410       constructs  such as loops or conditions; this somewhat illogical behav‐
411       iour can be recovered by setting the option CONTINUE_ON_ERROR.
412
413       Fatal errors found in non-interactive shells include:
414
415       •      Failure to parse shell options passed when invoking the shell
416
417       •      Failure to change options with the set builtin
418
419       •      Parse errors of all sorts, including failures to parse mathemat‐
420              ical expressions
421
422       •      Failures  to  set or modify variable behaviour with typeset, lo‐
423              cal, declare, export, integer, float
424
425       •      Execution of  incorrectly  positioned  loop  control  structures
426              (continue, break)
427
428       •      Attempts  to  use  regular expression with no regular expression
429              module available
430
431       •      Disallowed operations when the RESTRICTED options is set
432
433       •      Failure to create a pipe needed for a pipeline
434
435       •      Failure to create a multio
436
437       •      Failure to autoload a module needed for a declared shell feature
438
439       •      Errors creating command or process substitutions
440
441       •      Syntax errors in glob qualifiers
442
443       •      File generation errors where not caught by the  option  BAD_PAT‐
444              TERN
445
446       •      All bad patterns used for matching within case statements
447
448       •      File generation failures where not caused by NO_MATCH or similar
449              options
450
451       •      All file generation errors where the pattern was used to  create
452              a multio
453
454       •      Memory errors where detected by the shell
455
456       •      Invalid subscripts to shell variables
457
458       •      Attempts to assign read-only variables
459
460       •      Logical  errors  with  variables such as assignment to the wrong
461              type
462
463       •      Use of invalid variable names
464
465       •      Errors in variable substitution syntax
466
467       •      Failure to convert characters in $'...' expressions
468
469       If the POSIX_BUILTINS option is set, more errors associated with  shell
470       builtin  commands are treated as fatal, as specified by the POSIX stan‐
471       dard.
472

COMMENTS

474       In non-interactive shells, or in interactive shells with  the  INTERAC‐
475       TIVE_COMMENTS  option set, a word beginning with the third character of
476       the histchars parameter (`#' by default) causes that word and  all  the
477       following characters up to a newline to be ignored.
478

ALIASING

480       Every eligible word in the shell input is checked to see if there is an
481       alias defined for it.  If so, it is replaced by the text of  the  alias
482       if it is in command position (if it could be the first word of a simple
483       command), or if the alias is global.  If the replacement text ends with
484       a  space,  the next word in the shell input is always eligible for pur‐
485       poses of alias expansion.  An alias is defined using the alias builtin;
486       global aliases may be defined using the -g option to that builtin.
487
488       A word is defined as:
489
490       •      Any plain string or glob pattern
491
492       •      Any  quoted  string,  using  any  quoting  method (note that the
493              quotes must be part of the alias definition for this to be  eli‐
494              gible)
495
496       •      Any parameter reference or command substitution
497
498       •      Any  series of the foregoing, concatenated without whitespace or
499              other tokens between them
500
501       •      Any reserved word (case, do, else, etc.)
502
503       •      With global aliasing, any command separator, any redirection op‐
504              erator, and `(' or `)' when not part of a glob pattern
505
506       Alias  expansion  is done on the shell input before any other expansion
507       except history expansion.  Therefore, if an alias is  defined  for  the
508       word  foo,  alias expansion may be avoided by quoting part of the word,
509       e.g. \foo.  Any form of quoting works, although  there  is  nothing  to
510       prevent  an  alias  being  defined  for the quoted form such as \foo as
511       well.
512
513       When POSIX_ALIASES is set, only plain unquoted strings are eligible for
514       aliasing.   The  alias  builtin does not reject ineligible aliases, but
515       they are not expanded.
516
517       For use with completion, which would remove an initial  backslash  fol‐
518       lowed  by  a character that isn't special, it may be more convenient to
519       quote the word by starting with a single quote, i.e.  'foo;  completion
520       will automatically add the trailing single quote.
521
522   Alias difficulties
523       Although aliases can be used in ways that bend normal shell syntax, not
524       every string of non-white-space characters can be used as an alias.
525
526       Any set of characters not listed as a word above is not a  word,  hence
527       no  attempt  is  made to expand it as an alias, no matter how it is de‐
528       fined (i.e. via the builtin or the special parameter aliases  described
529       in the section THE ZSH/PARAMETER MODULE in zshmodules(1)).  However, as
530       noted in the case of POSIX_ALIASES above, the shell does not attempt to
531       deduce  whether  the string corresponds to a word at the time the alias
532       is created.
533
534       For example, an expression containing an = at the start  of  a  command
535       line  is  an assignment and cannot be expanded as an alias; a lone = is
536       not an assignment but can only be set as an alias using the  parameter,
537       as otherwise the = is taken part of the syntax of the builtin command.
538
539       It  is  not  presently possible to alias the `((' token that introduces
540       arithmetic expressions, because until a full statement has been parsed,
541       it  cannot be distinguished from two consecutive `(' tokens introducing
542       nested subshells.  Also, if a separator such  as  &&  is  aliased,  \&&
543       turns into the two tokens \& and &, each of which may have been aliased
544       separately.  Similarly for \<<, \>|, etc.
545
546       There is a commonly encountered problem with aliases illustrated by the
547       following code:
548
549              alias echobar='echo bar'; echobar
550
551       This  prints  a  message  that  the command echobar could not be found.
552       This happens because aliases are expanded when the code is read in; the
553       entire  line  is read in one go, so that when echobar is executed it is
554       too late to expand the newly defined alias.  This is often a problem in
555       shell scripts, functions, and code executed with `source' or `.'.  Con‐
556       sequently, use of functions  rather  than  aliases  is  recommended  in
557       non-interactive code.
558
559       Note  also  the  unhelpful  interaction of aliases and function defini‐
560       tions:
561
562              alias func='noglob func'
563              func() {
564                  echo Do something with $*
565              }
566
567       Because aliases are expanded in function definitions, this  causes  the
568       following command to be executed:
569
570              noglob func() {
571                  echo Do something with $*
572              }
573
574       which  defines noglob as well as func as functions with the body given.
575       To avoid this, either quote the name func or use the alternative  func‐
576       tion  definition  form  `function func'.  Ensuring the alias is defined
577       after the function works but is problematic if the code fragment  might
578       be re-executed.
579

QUOTING

581       A  character  may be quoted (that is, made to stand for itself) by pre‐
582       ceding it with a `\'.  `\' followed by a newline is ignored.
583
584       A string enclosed between `$'' and `'' is processed the same way as the
585       string arguments of the print builtin, and the resulting string is con‐
586       sidered to be entirely quoted.  A literal `'' character can be included
587       in the string by using the `\'' escape.
588
589       All  characters  enclosed  between a pair of single quotes ('') that is
590       not preceded by a `$' are quoted.  A single quote cannot appear  within
591       single  quotes unless the option RC_QUOTES is set, in which case a pair
592       of single quotes are turned into a single quote.  For example,
593
594              print ''''
595
596       outputs nothing apart from a newline if RC_QUOTES is not set,  but  one
597       single quote if it is set.
598
599       Inside  double  quotes  (""), parameter and command substitution occur,
600       and `\' quotes the characters `\', ``', `"', `$', and the first charac‐
601       ter of $histchars (default `!').
602

REDIRECTION

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

OPENING FILE DESCRIPTORS USING PARAMETERS

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

MULTIOS

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

REDIRECTIONS WITH NO COMMAND

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

COMMAND EXECUTION

920       If a command name contains no slashes, the shell attempts to locate it.
921       If there exists a shell function by that name, the function is  invoked
922       as  described  in  the  section  `Functions'.   If there exists a shell
923       builtin by that name, the builtin is invoked.
924
925       Otherwise, the shell searches each element of  $path  for  a  directory
926       containing  an  executable  file by that name.  If the search is unsuc‐
927       cessful, the shell prints an error message and returns a  nonzero  exit
928       status.
929
930       If  execution  fails  because the file is not in executable format, and
931       the file is not a directory, it  is  assumed  to  be  a  shell  script.
932       /bin/sh  is  spawned to execute it.  If the program is a file beginning
933       with `#!', the remainder of the first line specifies an interpreter for
934       the program.  The shell will execute the specified interpreter on oper‐
935       ating systems that do not handle this executable format in the kernel.
936
937       If no external command is found but a  function  command_not_found_han‐
938       dler  exists the shell executes this function with all command line ar‐
939       guments.  The return status of the function becomes the status  of  the
940       command.   If  the  function wishes to mimic the behaviour of the shell
941       when the command is not found, it should print the message `command not
942       found:  cmd'  to  standard  error and return status 127.  Note that the
943       handler is executed in a subshell forked to execute  an  external  com‐
944       mand,  hence changes to directories, shell parameters, etc. have no ef‐
945       fect on the main shell.
946

FUNCTIONS

948       Shell functions are defined with the function reserved word or the spe‐
949       cial  syntax `funcname ()'.  Shell functions are read in and stored in‐
950       ternally.  Alias names are resolved when the function is  read.   Func‐
951       tions  are  executed  like  commands with the arguments passed as posi‐
952       tional parameters.  (See the section `Command Execution'.)
953
954       Functions execute in the same process as the caller and share all files
955       and  present working directory with the caller.  A trap on EXIT set in‐
956       side a function is executed after the function completes in  the  envi‐
957       ronment of the caller.
958
959       The return builtin is used to return from function calls.
960
961       Function  identifiers  can be listed with the functions builtin.  Func‐
962       tions can be undefined with the unfunction builtin.
963

AUTOLOADING FUNCTIONS

965       A function can be marked as undefined using the  autoload  builtin  (or
966       `functions  -u'  or `typeset -fu').  Such a function has no body.  When
967       the function is first executed, the shell searches for  its  definition
968       using the elements of the fpath variable.  Thus to define functions for
969       autoloading, a typical sequence is:
970
971              fpath=(~/myfuncs $fpath)
972              autoload myfunc1 myfunc2 ...
973
974       The usual alias expansion during reading will be suppressed if the  au‐
975       toload builtin or its equivalent is given the option -U. This is recom‐
976       mended for the use of functions supplied  with  the  zsh  distribution.
977       Note  that  for functions precompiled with the zcompile builtin command
978       the flag -U must be provided when the .zwc file is created, as the cor‐
979       responding information is compiled into the latter.
980
981       For  each  element  in fpath, the shell looks for three possible files,
982       the newest of which is used to load the definition for the function:
983
984       element.zwc
985              A file created with the zcompile builtin command, which  is  ex‐
986              pected  to  contain the definitions for all functions in the di‐
987              rectory named element.  The file is treated in the  same  manner
988              as  a  directory  containing files for functions and is searched
989              for the definition of the function.   If the definition  is  not
990              found,  the  search for a definition proceeds with the other two
991              possibilities described below.
992
993              If element already includes a .zwc extension (i.e. the extension
994              was  explicitly  given by the user), element is searched for the
995              definition of the function without comparing its age to that  of
996              other  files;  in  fact, there does not need to be any directory
997              named element without the suffix.   Thus  including  an  element
998              such as `/usr/local/funcs.zwc' in fpath will speed up the search
999              for functions, with the  disadvantage  that  functions  included
1000              must  be  explicitly recompiled by hand before the shell notices
1001              any changes.
1002
1003       element/function.zwc
1004              A file created with zcompile, which is expected to  contain  the
1005              definition  for function.  It may include other function defini‐
1006              tions as well, but those are neither loaded nor executed; a file
1007              found  in  this way is searched only for the definition of func‐
1008              tion.
1009
1010       element/function
1011              A file of zsh command text, taken to be the definition for func‐
1012              tion.
1013
1014       In  summary, the order of searching is, first, in the parents of direc‐
1015       tories in fpath for the newer of either a compiled directory or  a  di‐
1016       rectory  in fpath; second, if more than one of these contains a defini‐
1017       tion for the function that is sought, the leftmost in the fpath is cho‐
1018       sen;  and  third,  within  a  directory, the newer of either a compiled
1019       function or an ordinary function definition is used.
1020
1021       If the KSH_AUTOLOAD option is set, or the file contains only  a  simple
1022       definition of the function, the file's contents will be executed.  This
1023       will normally define the function in question,  but  may  also  perform
1024       initialization, which is executed in the context of the function execu‐
1025       tion, and may therefore define local parameters.  It is an error if the
1026       function is not defined by loading the file.
1027
1028       Otherwise,  the  function body (with no surrounding `funcname() {...}')
1029       is taken to be the complete contents of the file.  This form allows the
1030       file  to be used directly as an executable shell script.  If processing
1031       of the file results in the function being re-defined, the function  it‐
1032       self  is not re-executed.  To force the shell to perform initialization
1033       and then call the function defined, the file should contain initializa‐
1034       tion code (which will be executed then discarded) in addition to a com‐
1035       plete function definition (which will be retained for subsequent  calls
1036       to the function), and a call to the shell function, including any argu‐
1037       ments, at the end.
1038
1039       For example, suppose the autoload file func contains
1040
1041              func() { print This is func; }
1042              print func is initialized
1043
1044       then `func; func' with KSH_AUTOLOAD set will produce both  messages  on
1045       the  first  call, but only the message `This is func' on the second and
1046       subsequent calls.  Without KSH_AUTOLOAD set, it will produce  the  ini‐
1047       tialization  message  on  the  first call, and the other message on the
1048       second and subsequent calls.
1049
1050       It is also possible to create a function that  is  not  marked  as  au‐
1051       toloaded, but which loads its own definition by searching fpath, by us‐
1052       ing `autoload -X' within a shell function.  For example, the  following
1053       are equivalent:
1054
1055              myfunc() {
1056                autoload -X
1057              }
1058              myfunc args...
1059
1060       and
1061
1062              unfunction myfunc   # if myfunc was defined
1063              autoload myfunc
1064              myfunc args...
1065
1066       In  fact,  the  functions  command outputs `builtin autoload -X' as the
1067       body of an autoloaded function.  This is done so that
1068
1069              eval "$(functions)"
1070
1071       produces a reasonable result.  A true autoloaded function can be  iden‐
1072       tified  by  the  presence of the comment `# undefined' in the body, be‐
1073       cause all comments are discarded from defined functions.
1074
1075       To load the definition of an autoloaded function myfunc without execut‐
1076       ing myfunc, use:
1077
1078              autoload +X myfunc
1079

ANONYMOUS FUNCTIONS

1081       If  no  name  is given for a function, it is `anonymous' and is handled
1082       specially.  Either form of function definition may be used: a `()' with
1083       no  preceding  name, or a `function' with an immediately following open
1084       brace.  The function is executed immediately at the point of definition
1085       and  is  not  stored  for  future  use.   The  function  name is set to
1086       `(anon)'.
1087
1088       Arguments to the function may be specified as words following the clos‐
1089       ing  brace  defining the function, hence if there are none no arguments
1090       (other than $0) are set.  This is a difference from the way other func‐
1091       tions  are  parsed: normal function definitions may be followed by cer‐
1092       tain keywords such as `else' or `fi', which will be  treated  as  argu‐
1093       ments  to anonymous functions, so that a newline or semicolon is needed
1094       to force keyword interpretation.
1095
1096       Note also that the argument list of any enclosing script or function is
1097       hidden  (as  would  be  the  case for any other function called at this
1098       point).
1099
1100       Redirections may be applied to the anonymous function in the same  man‐
1101       ner  as  to a current-shell structure enclosed in braces.  The main use
1102       of anonymous functions is to provide a scope for local variables.  This
1103       is  particularly  convenient  in start-up files as these do not provide
1104       their own local variable scope.
1105
1106       For example,
1107
1108              variable=outside
1109              function {
1110                local variable=inside
1111                print "I am $variable with arguments $*"
1112              } this and that
1113              print "I am $variable"
1114
1115       outputs the following:
1116
1117              I am inside with arguments this and that
1118              I am outside
1119
1120       Note that function definitions with arguments that expand  to  nothing,
1121       for  example `name=; function $name { ... }', are not treated as anony‐
1122       mous functions.  Instead, they are treated as normal  function  defini‐
1123       tions where the definition is silently discarded.
1124

SPECIAL FUNCTIONS

1126       Certain functions, if defined, have special meaning to the shell.
1127
1128   Hook Functions
1129       For the functions below, it is possible to define an array that has the
1130       same name as the function with `_functions' appended.  Any  element  in
1131       such an array is taken as the name of a function to execute; it is exe‐
1132       cuted in the same context and with the  same  arguments  as  the  basic
1133       function.   For example, if $chpwd_functions is an array containing the
1134       values `mychpwd', `chpwd_save_dirstack', then the shell attempts to ex‐
1135       ecute  the  functions  `chpwd', `mychpwd' and `chpwd_save_dirstack', in
1136       that order.  Any function that does not exist is silently  ignored.   A
1137       function  found  by  this mechanism is referred to elsewhere as a `hook
1138       function'.  An error in any function causes subsequent functions not to
1139       be  run.  Note further that an error in a precmd hook causes an immedi‐
1140       ately following periodic function not to run (though it may run at  the
1141       next opportunity).
1142
1143       chpwd  Executed whenever the current working directory is changed.
1144
1145       periodic
1146              If  the parameter PERIOD is set, this function is executed every
1147              $PERIOD seconds, just before a prompt.  Note  that  if  multiple
1148              functions  are  defined  using the array periodic_functions only
1149              one period is applied to the complete set of functions, and  the
1150              scheduled time is not reset if the list of functions is altered.
1151              Hence the set of functions is always called together.
1152
1153       precmd Executed before each prompt.  Note that precommand functions are
1154              not  re-executed  simply because the command line is redrawn, as
1155              happens, for example, when a notification about an  exiting  job
1156              is displayed.
1157
1158       preexec
1159              Executed  just  after a command has been read and is about to be
1160              executed.  If the history mechanism  is  active  (regardless  of
1161              whether  the  line  was  discarded from the history buffer), the
1162              string that the user typed is passed as the first argument, oth‐
1163              erwise  it  is an empty string.  The actual command that will be
1164              executed (including expanded aliases) is passed in two different
1165              forms:  the  second argument is a single-line, size-limited ver‐
1166              sion of the command (with things like function  bodies  elided);
1167              the  third  argument  contains  the full text that is being exe‐
1168              cuted.
1169
1170       zshaddhistory
1171              Executed when a history line has been  read  interactively,  but
1172              before  it  is executed.  The sole argument is the complete his‐
1173              tory line  (so  that  any  terminating  newline  will  still  be
1174              present).
1175
1176              If  any  of the hook functions returns status 1 (or any non-zero
1177              value other than 2, though this is  not  guaranteed  for  future
1178              versions  of  the shell) the history line will not be saved, al‐
1179              though it lingers in the history until the  next  line  is  exe‐
1180              cuted, allowing you to reuse or edit it immediately.
1181
1182              If  any  of the hook functions returns status 2 the history line
1183              will be saved on the internal history list, but not  written  to
1184              the  history  file.   In  case of a conflict, the first non-zero
1185              status value is taken.
1186
1187              A hook function may call `fc -p ...' to switch the history  con‐
1188              text  so  that the history is saved in a different file from the
1189              that in the global HISTFILE parameter.   This  is  handled  spe‐
1190              cially:  the history context is automatically restored after the
1191              processing of the history line is finished.
1192
1193              The following example function works with  one  of  the  options
1194              INC_APPEND_HISTORY  or SHARE_HISTORY set, in order that the line
1195              is written out immediately after the history entry is added.  It
1196              first  adds the history line to the normal history with the new‐
1197              line stripped, which is usually the correct behaviour.  Then  it
1198              switches the history context so that the line will be written to
1199              a history file in the current directory.
1200
1201                     zshaddhistory() {
1202                       print -sr -- ${1%%$'\n'}
1203                       fc -p .zsh_local_history
1204                     }
1205
1206       zshexit
1207              Executed at the point where the main shell is about to exit nor‐
1208              mally.   This  is  not called by exiting subshells, nor when the
1209              exec precommand modifier is used  before  an  external  command.
1210              Also, unlike TRAPEXIT, it is not called when functions exit.
1211
1212   Trap Functions
1213       The functions below are treated specially but do not have corresponding
1214       hook arrays.
1215
1216       TRAPNAL
1217              If defined and non-null, this function will be executed whenever
1218              the shell catches a signal SIGNAL, where NAL is a signal name as
1219              specified for the kill  builtin.   The  signal  number  will  be
1220              passed as the first parameter to the function.
1221
1222              If  a  function  of this form is defined and null, the shell and
1223              processes spawned by it will ignore SIGNAL.
1224
1225              The return status from the function is handled specially.  If it
1226              is  zero, the signal is assumed to have been handled, and execu‐
1227              tion continues normally.  Otherwise, the shell  will  behave  as
1228              interrupted  except  that  the  return status of the trap is re‐
1229              tained.
1230
1231              Programs terminated by uncaught  signals  typically  return  the
1232              status  128  plus the signal number.  Hence the following causes
1233              the handler for SIGINT to print a message, then mimic the  usual
1234              effect of the signal.
1235
1236                     TRAPINT() {
1237                       print "Caught SIGINT, aborting."
1238                       return $(( 128 + $1 ))
1239                     }
1240
1241              The  functions  TRAPZERR,  TRAPDEBUG and TRAPEXIT are never exe‐
1242              cuted inside other traps.
1243
1244       TRAPDEBUG
1245              If the option DEBUG_BEFORE_CMD is set (as it is by default), ex‐
1246              ecuted  before  each command; otherwise executed after each com‐
1247              mand.  See the description of the trap builtin in zshbuiltins(1)
1248              for details of additional features provided in debug traps.
1249
1250       TRAPEXIT
1251              Executed  when the shell exits, or when the current function ex‐
1252              its if defined inside a function.  The value of $? at the  start
1253              of  execution is the exit status of the shell or the return sta‐
1254              tus of the function exiting.
1255
1256       TRAPZERR
1257              Executed whenever a command has a non-zero  exit  status.   How‐
1258              ever,  the function is not executed if the command occurred in a
1259              sublist followed by `&&' or `||'; only the final  command  in  a
1260              sublist  of this type causes the trap to be executed.  The func‐
1261              tion TRAPERR acts the same as TRAPZERR on systems where there is
1262              no SIGERR (this is the usual case).
1263
1264       The  functions  beginning  `TRAP' may alternatively be defined with the
1265       trap builtin:  this may be preferable for some uses.   Setting  a  trap
1266       with  one  form removes any trap of the other form for the same signal;
1267       removing a trap in either form removes all traps for the  same  signal.
1268       The forms
1269
1270              TRAPNAL() {
1271               # code
1272              }
1273
1274       ('function traps') and
1275
1276              trap '
1277               # code
1278              ' NAL
1279
1280       ('list  traps')  are  equivalent in most ways, the exceptions being the
1281       following:
1282
1283       •      Function traps have all the properties of normal functions,  ap‐
1284              pearing in the list of functions and being called with their own
1285              function context rather than the  context  where  the  trap  was
1286              triggered.
1287
1288       •      The  return status from function traps is special, whereas a re‐
1289              turn from a list trap causes the surrounding context  to  return
1290              with the given status.
1291
1292       •      Function  traps  are  not  reset within subshells, in accordance
1293              with zsh behaviour; list traps are  reset,  in  accordance  with
1294              POSIX behaviour.
1295

JOBS

1297       If  the  MONITOR  option  is set, an interactive shell associates a job
1298       with each pipeline.  It keeps a table of current jobs, printed  by  the
1299       jobs  command,  and  assigns them small integer numbers.  When a job is
1300       started asynchronously with `&', the shell prints a  line  to  standard
1301       error which looks like:
1302
1303              [1] 1234
1304
1305       indicating that the job which was started asynchronously was job number
1306       1 and had one (top-level) process, whose process ID was 1234.
1307
1308       If a job is started with `&|' or `&!', then  that  job  is  immediately
1309       disowned.   After  startup,  it does not have a place in the job table,
1310       and is not subject to the job control features described here.
1311
1312       If you are running a job and wish to do something else you may hit  the
1313       key  ^Z (control-Z) which sends a TSTP signal to the current job:  this
1314       key may be redefined by the susp option of the external  stty  command.
1315       The  shell  will  then  normally  indicate  that the job has been `sus‐
1316       pended', and print another prompt.  You can then manipulate  the  state
1317       of  this  job, putting it in the background with the bg command, or run
1318       some other commands and then eventually bring the  job  back  into  the
1319       foreground  with  the foreground command fg.  A ^Z takes effect immedi‐
1320       ately and is like an interrupt in that pending output and unread  input
1321       are discarded when it is typed.
1322
1323       A job being run in the background will suspend if it tries to read from
1324       the terminal.
1325
1326       Note that if the job running in the foreground  is  a  shell  function,
1327       then  suspending  it will have the effect of causing the shell to fork.
1328       This is necessary to separate the function's state  from  that  of  the
1329       parent  shell performing the job control, so that the latter can return
1330       to the command line prompt.  As a result, even if fg is  used  to  con‐
1331       tinue  the job the function will no longer be part of the parent shell,
1332       and any variables set by the function will not be visible in the parent
1333       shell.   Thus  the behaviour is different from the case where the func‐
1334       tion was never suspended.  Zsh is different from many other  shells  in
1335       this regard.
1336
1337       One  additional side effect is that use of disown with a job created by
1338       suspending shell code in this fashion is delayed: the job can  only  be
1339       disowned once any process started from the parent shell has terminated.
1340       At that point, the disowned job disappears silently from the job list.
1341
1342       The same behaviour is found when the shell is  executing  code  as  the
1343       right  hand  side  of a pipeline or any complex shell construct such as
1344       if, for, etc., in order that the entire block of code can be managed as
1345       a  single job.  Background jobs are normally allowed to produce output,
1346       but this can be disabled by giving the command `stty tostop'.   If  you
1347       set this tty option, then background jobs will suspend when they try to
1348       produce output like they do when they try to read input.
1349
1350       When a command is suspended and continued later with  the  fg  or  wait
1351       builtins,  zsh  restores tty modes that were in effect when it was sus‐
1352       pended.  This (intentionally) does not apply if the command is  contin‐
1353       ued via `kill -CONT', nor when it is continued with bg.
1354
1355       There are several ways to refer to jobs in the shell.  A job can be re‐
1356       ferred to by the process ID of any process of the job or by one of  the
1357       following:
1358
1359       %number
1360              The job with the given number.
1361       %string
1362              The last job whose command line begins with string.
1363       %?string
1364              The last job whose command line contains string.
1365       %%     Current job.
1366       %+     Equivalent to `%%'.
1367       %-     Previous job.
1368
1369       The shell learns immediately whenever a process changes state.  It nor‐
1370       mally informs you whenever a job becomes blocked  so  that  no  further
1371       progress  is possible.  If the NOTIFY option is not set, it waits until
1372       just before it prints a prompt before it informs you.  All such notifi‐
1373       cations  are  sent directly to the terminal, not to the standard output
1374       or standard error.
1375
1376       When the monitor mode is on, each background job that  completes  trig‐
1377       gers any trap set for CHLD.
1378
1379       When  you  try  to leave the shell while jobs are running or suspended,
1380       you will be warned that `You have suspended (running) jobs'.   You  may
1381       use  the  jobs command to see what they are.  If you do this or immedi‐
1382       ately try to exit again, the shell will not warn you a second time; the
1383       suspended  jobs will be terminated, and the running jobs will be sent a
1384       SIGHUP signal, if the HUP option is set.
1385
1386       To avoid having the shell terminate the running jobs,  either  use  the
1387       nohup command (see nohup(1)) or the disown builtin.
1388

SIGNALS

1390       The INT and QUIT signals for an invoked command are ignored if the com‐
1391       mand is followed by `&' and the MONITOR  option  is  not  active.   The
1392       shell  itself  always ignores the QUIT signal.  Otherwise, signals have
1393       the values inherited by the shell from its parent (but see the  TRAPNAL
1394       special functions in the section `Functions').
1395
1396       Certain  jobs  are run asynchronously by the shell other than those ex‐
1397       plicitly put into the background; even in cases where the  shell  would
1398       usually wait for such jobs, an explicit exit command or exit due to the
1399       option ERR_EXIT will cause the shell to exit without waiting.  Examples
1400       of  such  asynchronous  jobs  are process substitution, see the section
1401       PROCESS SUBSTITUTION in the zshexpn(1) manual  page,  and  the  handler
1402       processes for multios, see the section MULTIOS in the zshmisc(1) manual
1403       page.
1404

ARITHMETIC EVALUATION

1406       The shell can perform integer and floating point arithmetic, either us‐
1407       ing  the  builtin let, or via a substitution of the form $((...)).  For
1408       integers, the shell is usually compiled to use 8-byte  precision  where
1409       this is available, otherwise precision is 4 bytes.  This can be tested,
1410       for example, by giving the command `print - $(( 12345678901 ))'; if the
1411       number  appears unchanged, the precision is at least 8 bytes.  Floating
1412       point arithmetic always uses the `double'  type  with  whatever  corre‐
1413       sponding precision is provided by the compiler and the library.
1414
1415       The let builtin command takes arithmetic expressions as arguments; each
1416       is evaluated separately.  Since many of the  arithmetic  operators,  as
1417       well  as  spaces, require quoting, an alternative form is provided: for
1418       any command which begins with a `((', all the characters until a match‐
1419       ing  `))'  are  treated as a quoted expression and arithmetic expansion
1420       performed as for an argument of  let.   More  precisely,  `((...))'  is
1421       equivalent  to  `let  "..."'.  The return status is 0 if the arithmetic
1422       value of the expression is non-zero, 1 if it is zero, and 2 if an error
1423       occurred.
1424
1425       For example, the following statement
1426
1427              (( val = 2 + 1 ))
1428
1429       is equivalent to
1430
1431              let "val = 2 + 1"
1432
1433       both  assigning  the  value 3 to the shell variable val and returning a
1434       zero status.
1435
1436       Integers can be in bases other than 10.  A leading `0x' or `0X' denotes
1437       hexadecimal and a leading `0b' or `0B' binary.  Integers may also be of
1438       the form `base#n', where base is  a  decimal  number  between  two  and
1439       thirty-six  representing  the arithmetic base and n is a number in that
1440       base (for example, `16#ff' is 255 in hexadecimal).  The base# may  also
1441       be omitted, in which case base 10 is used.  For backwards compatibility
1442       the form `[base]n' is also accepted.
1443
1444       An integer expression or a base given in the form `base#n' may  contain
1445       underscores  (`_')  after  the leading digit for visual guidance; these
1446       are ignored in computation.   Examples  are  1_000_000  or  0xffff_ffff
1447       which are equivalent to 1000000 and 0xffffffff respectively.
1448
1449       It is also possible to specify a base to be used for output in the form
1450       `[#base]', for example `[#16]'.  This is used  when  outputting  arith‐
1451       metical  substitutions  or  when assigning to scalar parameters, but an
1452       explicitly defined integer or floating point parameter will not be  af‐
1453       fected.   If an integer variable is implicitly defined by an arithmetic
1454       expression, any base specified in this way will be  set  as  the  vari‐
1455       able's output arithmetic base as if the option `-i base' to the typeset
1456       builtin had been used.  The expression has no precedence and if it  oc‐
1457       curs  more than once in a mathematical expression, the last encountered
1458       is used.  For clarity it is recommended that it appear at the beginning
1459       of an expression.  As an example:
1460
1461              typeset -i 16 y
1462              print $(( [#8] x = 32, y = 32 ))
1463              print $x $y
1464
1465       outputs first `8#40', the rightmost value in the given output base, and
1466       then `8#40 16#20', because y has been explicitly declared to have  out‐
1467       put base 16, while x (assuming it does not already exist) is implicitly
1468       typed by the arithmetic evaluation, where it acquires the  output  base
1469       8.
1470
1471       The base may be replaced or followed by an underscore, which may itself
1472       be followed by a positive integer (if it is  missing  the  value  3  is
1473       used).   This  indicates  that  underscores should be inserted into the
1474       output string, grouping the number for visual clarity.   The  following
1475       integer specifies the number of digits to group together.  For example:
1476
1477              setopt cbases
1478              print $(( [#16_4] 65536 ** 2 ))
1479
1480       outputs `0x1_0000_0000'.
1481
1482       The  feature can be used with floating point numbers, in which case the
1483       base must be omitted; grouping is away from the decimal point.  For ex‐
1484       ample,
1485
1486              zmodload zsh/mathfunc
1487              print $(( [#_] sqrt(1e7) ))
1488
1489       outputs  `3_162.277_660_168_379_5'  (the number of decimal places shown
1490       may vary).
1491
1492       If the C_BASES option is set, hexadecimal numbers  are  output  in  the
1493       standard C format, for example `0xFF' instead of the usual `16#FF'.  If
1494       the option OCTAL_ZEROES is also set (it is not by default), octal  num‐
1495       bers  will  be  treated  similarly and hence appear as `077' instead of
1496       `8#77'.  This option has no effect on the output of  bases  other  than
1497       hexadecimal  and  octal, and these formats are always understood on in‐
1498       put.
1499
1500       When an output base is specified using the `[#base]' syntax, an  appro‐
1501       priate  base prefix will be output if necessary, so that the value out‐
1502       put is valid syntax for input.   If  the  #  is  doubled,  for  example
1503       `[##16]', then no base prefix is output.
1504
1505       Floating  point  constants  are recognized by the presence of a decimal
1506       point or an exponent.  The decimal point may be the first character  of
1507       the  constant, but the exponent character e or E may not, as it will be
1508       taken for a parameter name.  All numeric parts (before  and  after  the
1509       decimal  point  and  in the exponent) may contain underscores after the
1510       leading digit for visual guidance; these are ignored in computation.
1511
1512       An arithmetic expression uses nearly the same syntax and  associativity
1513       of expressions as in C.
1514
1515       In  the native mode of operation, the following operators are supported
1516       (listed in decreasing order of precedence):
1517
1518       + - ! ~ ++ --
1519              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1520              ment
1521       << >>  bitwise shift left, right
1522       &      bitwise AND
1523       ^      bitwise XOR
1524       |      bitwise OR
1525       **     exponentiation
1526       * / %  multiplication, division, modulus (remainder)
1527       + -    addition, subtraction
1528       < > <= >=
1529              comparison
1530       == !=  equality and inequality
1531       &&     logical AND
1532       || ^^  logical OR, XOR
1533       ? :    ternary operator
1534       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1535              assignment
1536       ,      comma operator
1537
1538       The  operators  `&&',  `||', `&&=', and `||=' are short-circuiting, and
1539       only one of the latter two expressions in a ternary operator is  evalu‐
1540       ated.  Note the precedence of the bitwise AND, OR, and XOR operators.
1541
1542       With the option C_PRECEDENCES the precedences (but no other properties)
1543       of the operators are altered to be the same as those in most other lan‐
1544       guages that support the relevant operators:
1545
1546       + - ! ~ ++ --
1547              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre‐
1548              ment
1549       **     exponentiation
1550       * / %  multiplication, division, modulus (remainder)
1551       + -    addition, subtraction
1552       << >>  bitwise shift left, right
1553       < > <= >=
1554              comparison
1555       == !=  equality and inequality
1556       &      bitwise AND
1557       ^      bitwise XOR
1558       |      bitwise OR
1559       &&     logical AND
1560       ^^     logical XOR
1561       ||     logical OR
1562       ? :    ternary operator
1563       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
1564              assignment
1565       ,      comma operator
1566
1567       Note the precedence of exponentiation in both cases is  below  that  of
1568       unary  operators, hence `-3**2' evaluates as `9', not `-9'.  Use paren‐
1569       theses where necessary: `-(3**2)'.   This  is  for  compatibility  with
1570       other shells.
1571
1572       Mathematical  functions  can  be  called  with the syntax `func(args)',
1573       where the function decides if the  args  is  used  as  a  string  or  a
1574       comma-separated list of arithmetic expressions. The shell currently de‐
1575       fines no mathematical functions by default, but the module zsh/mathfunc
1576       may  be  loaded  with the zmodload builtin to provide standard floating
1577       point mathematical functions.
1578
1579       An expression of the form `##x' where x is any character sequence  such
1580       as `a', `^A', or `\M-\C-x' gives the value of this character and an ex‐
1581       pression of the form `#name' gives the value of the first character  of
1582       the  contents of the parameter name.  Character values are according to
1583       the character set used in the current locale; for  multibyte  character
1584       handling the option MULTIBYTE must be set.  Note that this form is dif‐
1585       ferent from `$#name', a standard parameter substitution which gives the
1586       length  of  the  parameter name.  `#\' is accepted instead of `##', but
1587       its use is deprecated.
1588
1589       Named parameters and subscripted  arrays  can  be  referenced  by  name
1590       within  an  arithmetic expression without using the parameter expansion
1591       syntax.  For example,
1592
1593              ((val2 = val1 * 2))
1594
1595       assigns twice the value of $val1 to the parameter named val2.
1596
1597       An internal integer representation of a named parameter can  be  speci‐
1598       fied  with  the integer builtin.  Arithmetic evaluation is performed on
1599       the value of each assignment to a named parameter declared  integer  in
1600       this  manner.   Assigning a floating point number to an integer results
1601       in rounding towards zero.
1602
1603       Likewise, floating  point  numbers  can  be  declared  with  the  float
1604       builtin; there are two types, differing only in their output format, as
1605       described for the typeset builtin.  The output format can  be  bypassed
1606       by using arithmetic substitution instead of the parameter substitution,
1607       i.e. `${float}' uses  the  defined  format,  but  `$((float))'  uses  a
1608       generic floating point format.
1609
1610       Promotion of integer to floating point values is performed where neces‐
1611       sary.  In addition, if any operator which  requires  an  integer  (`&',
1612       `|',  `^', `<<', `>>' and their equivalents with assignment) is given a
1613       floating point argument, it will be silently rounded towards  zero  ex‐
1614       cept for `~' which rounds down.
1615
1616       Users  should  beware  that, in common with many other programming lan‐
1617       guages but not software designed for calculation, the evaluation of  an
1618       expression  in  zsh is taken a term at a time and promotion of integers
1619       to floating point does not occur in terms only containing integers.   A
1620       typical  result of this is that a division such as 6/8 is truncated, in
1621       this being rounded towards 0.  The FORCE_FLOAT shell option can be used
1622       in  scripts  or  functions  where floating point evaluation is required
1623       throughout.
1624
1625       Scalar variables can hold integer or floating point values at different
1626       times; there is no memory of the numeric type in this case.
1627
1628       If a variable is first assigned in a numeric context without previously
1629       being declared, it will be implicitly typed as integer or float and re‐
1630       tain that type either until the type is explicitly changed or until the
1631       end of the scope.  This can have unforeseen consequences.  For example,
1632       in the loop
1633
1634              for (( f = 0; f < 1; f += 0.1 )); do
1635              # use $f
1636              done
1637
1638       if  f has not already been declared, the first assignment will cause it
1639       to be created as an integer, and consequently the operation `f +=  0.1'
1640       will  always cause the result to be truncated to zero, so that the loop
1641       will fail.  A simple fix would be to turn the initialization into `f  =
1642       0.0'.   It is therefore best to declare numeric variables with explicit
1643       types.
1644

CONDITIONAL EXPRESSIONS

1646       A conditional expression is used with the [[ compound command  to  test
1647       attributes  of  files  and  to compare strings.  Each expression can be
1648       constructed from one or more of the following unary or  binary  expres‐
1649       sions:
1650
1651       -a file
1652              true if file exists.
1653
1654       -b file
1655              true if file exists and is a block special file.
1656
1657       -c file
1658              true if file exists and is a character special file.
1659
1660       -d file
1661              true if file exists and is a directory.
1662
1663       -e file
1664              true if file exists.
1665
1666       -f file
1667              true if file exists and is a regular file.
1668
1669       -g file
1670              true if file exists and has its setgid bit set.
1671
1672       -h file
1673              true if file exists and is a symbolic link.
1674
1675       -k file
1676              true if file exists and has its sticky bit set.
1677
1678       -n string
1679              true if length of string is non-zero.
1680
1681       -o option
1682              true if option named option is on.  option may be a single char‐
1683              acter, in which case it is a single letter  option  name.   (See
1684              the section `Specifying Options'.)
1685
1686              When  no  option named option exists, and the POSIX_BUILTINS op‐
1687              tion hasn't been set, return 3 with a warning.  If  that  option
1688              is set, return 1 with no warning.
1689
1690       -p file
1691              true if file exists and is a FIFO special file (named pipe).
1692
1693       -r file
1694              true if file exists and is readable by current process.
1695
1696       -s file
1697              true if file exists and has size greater than zero.
1698
1699       -t fd  true  if file descriptor number fd is open and associated with a
1700              terminal device.  (note: fd is not optional)
1701
1702       -u file
1703              true if file exists and has its setuid bit set.
1704
1705       -v varname
1706              true if shell variable varname is set.
1707
1708       -w file
1709              true if file exists and is writable by current process.
1710
1711       -x file
1712              true if file exists and is executable by  current  process.   If
1713              file  exists  and  is  a directory, then the current process has
1714              permission to search in the directory.
1715
1716       -z string
1717              true if length of string is zero.
1718
1719       -L file
1720              true if file exists and is a symbolic link.
1721
1722       -O file
1723              true if file exists and is owned by the  effective  user  ID  of
1724              this process.
1725
1726       -G file
1727              true if file exists and its group matches the effective group ID
1728              of this process.
1729
1730       -S file
1731              true if file exists and is a socket.
1732
1733       -N file
1734              true if file exists and its access time is not  newer  than  its
1735              modification time.
1736
1737       file1 -nt file2
1738              true if file1 exists and is newer than file2.
1739
1740       file1 -ot file2
1741              true if file1 exists and is older than file2.
1742
1743       file1 -ef file2
1744              true if file1 and file2 exist and refer to the same file.
1745
1746       string = pattern
1747       string == pattern
1748              true  if  string  matches  pattern.   The  two forms are exactly
1749              equivalent.  The `=' form is the traditional shell  syntax  (and
1750              hence the only one generally used with the test and [ builtins);
1751              the `==' form provides compatibility with other  sorts  of  com‐
1752              puter language.
1753
1754       string != pattern
1755              true if string does not match pattern.
1756
1757       string =~ regexp
1758              true  if  string  matches the regular expression regexp.  If the
1759              option RE_MATCH_PCRE is set regexp is tested as a  PCRE  regular
1760              expression  using  the  zsh/pcre  module, else it is tested as a
1761              POSIX extended regular expression using  the  zsh/regex  module.
1762              Upon  successful match, some variables will be updated; no vari‐
1763              ables are changed if the matching fails.
1764
1765              If the option BASH_REMATCH is not set the scalar parameter MATCH
1766              is set to the substring that matched the pattern and the integer
1767              parameters MBEGIN and MEND to the index of the  start  and  end,
1768              respectively,  of  the  match  in string, such that if string is
1769              contained in variable var the expression `${var[$MBEGIN,$MEND]}'
1770              is  identical to `$MATCH'.  The setting of the option KSH_ARRAYS
1771              is respected.  Likewise, the array match  is  set  to  the  sub‐
1772              strings that matched parenthesised subexpressions and the arrays
1773              mbegin and mend to the indices of the start and  end  positions,
1774              respectively,  of  the substrings within string.  The arrays are
1775              not set if there were no parenthesised subexpressions.  For  ex‐
1776              ample,  if  the  string  `a short string' is matched against the
1777              regular expression `s(...)t', then (assuming the option  KSH_AR‐
1778              RAYS  is  not  set) MATCH, MBEGIN and MEND are `short', 3 and 7,
1779              respectively, while match, mbegin and mend are single entry  ar‐
1780              rays containing the strings `hor', `4' and `6', respectively.
1781
1782              If  the option BASH_REMATCH is set the array BASH_REMATCH is set
1783              to the substring that matched the pattern followed by  the  sub‐
1784              strings  that  matched  parenthesised  subexpressions within the
1785              pattern.
1786
1787       string1 < string2
1788              true if string1 comes before string2 based  on  ASCII  value  of
1789              their characters.
1790
1791       string1 > string2
1792              true  if  string1  comes  after  string2 based on ASCII value of
1793              their characters.
1794
1795       exp1 -eq exp2
1796              true if exp1 is numerically equal to exp2.  Note that for purely
1797              numeric  comparisons use of the ((...)) builtin described in the
1798              section `ARITHMETIC EVALUATION' is more convenient  than  condi‐
1799              tional expressions.
1800
1801       exp1 -ne exp2
1802              true if exp1 is numerically not equal to exp2.
1803
1804       exp1 -lt exp2
1805              true if exp1 is numerically less than exp2.
1806
1807       exp1 -gt exp2
1808              true if exp1 is numerically greater than exp2.
1809
1810       exp1 -le exp2
1811              true if exp1 is numerically less than or equal to exp2.
1812
1813       exp1 -ge exp2
1814              true if exp1 is numerically greater than or equal to exp2.
1815
1816       ( exp )
1817              true if exp is true.
1818
1819       ! exp  true if exp is false.
1820
1821       exp1 && exp2
1822              true if exp1 and exp2 are both true.
1823
1824       exp1 || exp2
1825              true if either exp1 or exp2 is true.
1826
1827       For  compatibility, if there is a single argument that is not syntacti‐
1828       cally significant, typically a variable, the condition is treated as  a
1829       test for whether the expression expands as a string of non-zero length.
1830       In other words, [[ $var ]] is the same as [[ -n $var ]].  It is  recom‐
1831       mended that the second, explicit, form be used where possible.
1832
1833       Normal shell expansion is performed on the file, string and pattern ar‐
1834       guments, but the result of each expansion is constrained to be a single
1835       word, similar to the effect of double quotes.
1836
1837       Filename  generation is not performed on any form of argument to condi‐
1838       tions.  However, it can be forced in any case where normal shell expan‐
1839       sion  is  valid and when the option EXTENDED_GLOB is in effect by using
1840       an explicit glob qualifier of the form (#q) at the end of  the  string.
1841       A  normal  glob qualifier expression may appear between the `q' and the
1842       closing parenthesis; if none appears the expression has no  effect  be‐
1843       yond  causing  filename generation.  The results of filename generation
1844       are joined together to form a single word, as with the results of other
1845       forms of expansion.
1846
1847       This  special  use of filename generation is only available with the [[
1848       syntax.  If the condition occurs within the [ or test builtin  commands
1849       then  globbing  occurs instead as part of normal command line expansion
1850       before the condition is evaluated.  In this case it may generate multi‐
1851       ple words which are likely to confuse the syntax of the test command.
1852
1853       For example,
1854
1855              [[ -n file*(#qN) ]]
1856
1857       produces  status  zero if and only if there is at least one file in the
1858       current directory beginning with the string `file'.  The globbing qual‐
1859       ifier  N  ensures  that the expression is empty if there is no matching
1860       file.
1861
1862       Pattern metacharacters are active for the pattern arguments;  the  pat‐
1863       terns  are  the  same  as  those used for filename generation, see zsh‐
1864       expn(1), but there is no special behaviour of `/' nor initial dots, and
1865       no glob qualifiers are allowed.
1866
1867       In  each  of the above expressions, if file is of the form `/dev/fd/n',
1868       where n is an integer, then the test applied to the open file whose de‐
1869       scriptor  number  is  n, even if the underlying system does not support
1870       the /dev/fd directory.
1871
1872       In the forms which do numeric comparison, the expressions  exp  undergo
1873       arithmetic expansion as if they were enclosed in $((...)).
1874
1875       For example, the following:
1876
1877              [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.
1878
1879       tests if either file foo or file bar exists, and if so, if the value of
1880       the parameter report begins with `y';  if  the  complete  condition  is
1881       true, the message `File exists.' is printed.
1882

EXPANSION OF PROMPT SEQUENCES

1884       Prompt sequences undergo a special form of expansion.  This type of ex‐
1885       pansion is also available using the -P option to the print builtin.
1886
1887       If the PROMPT_SUBST option is set, the prompt string is first subjected
1888       to  parameter expansion, command substitution and arithmetic expansion.
1889       See zshexpn(1).
1890
1891       Certain escape sequences may be recognised in the prompt string.
1892
1893       If the PROMPT_BANG option is set, a `!' in the prompt  is  replaced  by
1894       the  current  history  event  number.  A literal `!' may then be repre‐
1895       sented as `!!'.
1896
1897       If the PROMPT_PERCENT option is  set,  certain  escape  sequences  that
1898       start  with  `%'  are  expanded.  Many escapes are followed by a single
1899       character, although some of these take  an  optional  integer  argument
1900       that  should  appear  between the `%' and the next character of the se‐
1901       quence.  More complicated escape sequences  are  available  to  provide
1902       conditional expansion.
1903

SIMPLE PROMPT ESCAPES

1905   Special characters
1906       %%     A `%'.
1907
1908       %)     A `)'.
1909
1910   Login information
1911       %l     The line (tty) the user is logged in on, without `/dev/' prefix.
1912              If the name starts with `/dev/tty', that prefix is stripped.
1913
1914       %M     The full machine hostname.
1915
1916       %m     The hostname up to the first `.'.  An integer may follow the `%'
1917              to  specify  how  many  components  of the hostname are desired.
1918              With a negative integer, trailing components of the hostname are
1919              shown.
1920
1921       %n     $USERNAME.
1922
1923       %y     The line (tty) the user is logged in on, without `/dev/' prefix.
1924              This does not treat `/dev/tty' names specially.
1925
1926   Shell state
1927       %#     A `#' if the shell is running with privileges,  a  `%'  if  not.
1928              Equivalent  to `%(!.#.%%)'.  The definition of `privileged', for
1929              these purposes, is that either the effective user  ID  is  zero,
1930              or,  if  POSIX.1e  capabilities are supported, that at least one
1931              capability is raised in either the Effective or Inheritable  ca‐
1932              pability vectors.
1933
1934       %?     The  return  status of the last command executed just before the
1935              prompt.
1936
1937       %_     The status of the parser, i.e. the shell constructs  (like  `if'
1938              and  `for') that have been started on the command line. If given
1939              an integer number that many strings will  be  printed;  zero  or
1940              negative  or  no integer means print as many as there are.  This
1941              is most useful in prompts PS2 for continuation lines and PS4 for
1942              debugging  with  the  XTRACE  option; in the latter case it will
1943              also work non-interactively.
1944
1945       %^     The status of the parser in reverse. This is the  same  as  `%_'
1946              other than the order of strings.  It is often used in RPS2.
1947
1948       %d
1949       %/     Current  working  directory.   If an integer follows the `%', it
1950              specifies a number of trailing components of the current working
1951              directory  to show; zero means the whole path.  A negative inte‐
1952              ger specifies leading components, i.e. %-1d specifies the  first
1953              component.
1954
1955       %~     As  %d  and %/, but if the current working directory starts with
1956              $HOME, that part is replaced by a `~'. Furthermore, if it has  a
1957              named  directory  as  its prefix, that part is replaced by a `~'
1958              followed by the name of the directory, but only if the result is
1959              shorter  than the full path; see Dynamic and Static named direc‐
1960              tories in zshexpn(1).
1961
1962       %e     Evaluation depth of the current sourced file, shell function, or
1963              eval.   This  is incremented or decremented every time the value
1964              of %N is set or reverted  to  a  previous  value,  respectively.
1965              This is most useful for debugging as part of $PS4.
1966
1967       %h
1968       %!     Current history event number.
1969
1970       %i     The  line number currently being executed in the script, sourced
1971              file, or shell function given by %N.  This is  most  useful  for
1972              debugging as part of $PS4.
1973
1974       %I     The  line  number currently being executed in the file %x.  This
1975              is similar to %i, but the line number is always a line number in
1976              the file where the code was defined, even if the code is a shell
1977              function.
1978
1979       %j     The number of jobs.
1980
1981       %L     The current value of $SHLVL.
1982
1983       %N     The name of the script, sourced file, or shell function that zsh
1984              is currently executing, whichever was started most recently.  If
1985              there is none, this is equivalent to the parameter $0.  An inte‐
1986              ger may follow the `%' to specify a number of trailing path com‐
1987              ponents to show; zero means the full path.  A  negative  integer
1988              specifies leading components.
1989
1990       %x     The  name of the file containing the source code currently being
1991              executed.  This behaves as %N except that function and eval com‐
1992              mand  names  are not shown, instead the file where they were de‐
1993              fined.
1994
1995       %c
1996       %.
1997       %C     Trailing component of the current working directory.  An integer
1998              may  follow the `%' to get more than one component.  Unless `%C'
1999              is used, tilde contraction is performed first.  These are depre‐
2000              cated  as %c and %C are equivalent to %1~ and %1/, respectively,
2001              while explicit positive integers have the same effect as for the
2002              latter two sequences.
2003
2004   Date and time
2005       %D     The date in yy-mm-dd format.
2006
2007       %T     Current time of day, in 24-hour format.
2008
2009       %t
2010       %@     Current time of day, in 12-hour, am/pm format.
2011
2012       %*     Current time of day in 24-hour format, with seconds.
2013
2014       %w     The date in day-dd format.
2015
2016       %W     The date in mm/dd/yy format.
2017
2018       %D{string}
2019              string  is  formatted  using  the  strftime function.  See strf‐
2020              time(3) for more details.  Various zsh extensions  provide  num‐
2021              bers  with  no  leading  zero or space if the number is a single
2022              digit:
2023
2024              %f     a day of the month
2025              %K     the hour of the day on the 24-hour clock
2026              %L     the hour of the day on the 12-hour clock
2027
2028              In addition, if the system supports the POSIX gettimeofday  sys‐
2029              tem  call,  %.  provides decimal fractions of a second since the
2030              epoch with leading zeroes.  By default three decimal places  are
2031              provided,  but a number of digits up to 9 may be given following
2032              the %; hence %6.  outputs microseconds, and %9. outputs nanosec‐
2033              onds.   (The  latter  requires a nanosecond-precision clock_get‐
2034              time; systems lacking this will return a value multiplied by the
2035              appropriate power of 10.)  A typical example of this is the for‐
2036              mat `%D{%H:%M:%S.%.}'.
2037
2038              The GNU extension %N is handled as a synonym for %9..
2039
2040              Additionally, the GNU extension that a `-' between the % and the
2041              format  character  causes a leading zero or space to be stripped
2042              is handled directly by the shell for the format characters d, f,
2043              H, k, l, m, M, S and y; any other format characters are provided
2044              to the system's strftime(3) with any leading `-' present, so the
2045              handling is system dependent.  Further GNU (or other) extensions
2046              are also passed to strftime(3) and may work if the  system  sup‐
2047              ports them.
2048
2049   Visual effects
2050       %B (%b)
2051              Start (stop) boldface mode.
2052
2053       %E     Clear to end of line.
2054
2055       %U (%u)
2056              Start (stop) underline mode.
2057
2058       %S (%s)
2059              Start (stop) standout mode.
2060
2061       %F (%f)
2062              Start  (stop)  using a different foreground colour, if supported
2063              by the terminal.  The colour may be specified two  ways:  either
2064              as  a  numeric  argument,  as normal, or by a sequence in braces
2065              following the %F, for example %F{red}.  In the latter  case  the
2066              values  allowed are as described for the fg zle_highlight attri‐
2067              bute; see Character Highlighting in zshzle(1).  This means  that
2068              numeric colours are allowed in the second format also.
2069
2070       %K (%k)
2071              Start (stop) using a different bacKground colour.  The syntax is
2072              identical to that for %F and %f.
2073
2074       %{...%}
2075              Include a string as  a  literal  escape  sequence.   The  string
2076              within  the braces should not change the cursor position.  Brace
2077              pairs can nest.
2078
2079              A positive numeric argument between the % and the {  is  treated
2080              as described for %G below.
2081
2082       %G     Within  a  %{...%} sequence, include a `glitch': that is, assume
2083              that a single character width will be output.   This  is  useful
2084              when  outputting  characters  that otherwise cannot be correctly
2085              handled by the shell, such as the  alternate  character  set  on
2086              some  terminals.   The  characters  in  question can be included
2087              within a %{...%} sequence together with the  appropriate  number
2088              of  %G  sequences to indicate the correct width.  An integer be‐
2089              tween the `%' and `G' indicates a  character  width  other  than
2090              one.   Hence  %{seq%2G%} outputs seq and assumes it takes up the
2091              width of two standard characters.
2092
2093              Multiple uses of %G accumulate in the obvious fashion; the posi‐
2094              tion  of  the %G is unimportant.  Negative integers are not han‐
2095              dled.
2096
2097              Note that when prompt truncation is in use it  is  advisable  to
2098              divide  up  output  into  single  characters within each %{...%}
2099              group so that the correct truncation point can be found.
2100

CONDITIONAL SUBSTRINGS IN PROMPTS

2102       %v     The value of the first element of  the  psvar  array  parameter.
2103              Following  the `%' with an integer gives that element of the ar‐
2104              ray.  Negative integers count from the end of the array.
2105
2106       %(x.true-text.false-text)
2107              Specifies a ternary expression.  The character following  the  x
2108              is  arbitrary;  the  same character is used to separate the text
2109              for the `true' result from that for the  `false'  result.   This
2110              separator  may  not appear in the true-text, except as part of a
2111              %-escape sequence.  A `)' may appear in the false-text as  `%)'.
2112              true-text and false-text may both contain arbitrarily-nested es‐
2113              cape sequences, including further ternary expressions.
2114
2115              The left parenthesis may be preceded or followed by  a  positive
2116              integer  n,  which defaults to zero.  A negative integer will be
2117              multiplied by -1, except as noted below for `l'.  The test char‐
2118              acter x may be any of the following:
2119
2120              !      True if the shell is running with privileges.
2121              #      True if the effective uid of the current process is n.
2122              ?      True if the exit status of the last command was n.
2123              _      True if at least n shell constructs were started.
2124              C
2125              /      True if the current absolute path has at least n elements
2126                     relative to the root directory, hence / is counted  as  0
2127                     elements.
2128              c
2129              .
2130              ~      True if the current path, with prefix replacement, has at
2131                     least n elements relative to the root directory, hence  /
2132                     is counted as 0 elements.
2133              D      True if the month is equal to n (January = 0).
2134              d      True if the day of the month is equal to n.
2135              e      True if the evaluation depth is at least n.
2136              g      True if the effective gid of the current process is n.
2137              j      True if the number of jobs is at least n.
2138              L      True if the SHLVL parameter is at least n.
2139              l      True  if  at least n characters have already been printed
2140                     on the current line.  When n  is  negative,  true  if  at
2141                     least abs(n) characters remain before the opposite margin
2142                     (thus the left margin for RPROMPT).
2143              S      True if the SECONDS parameter is at least n.
2144              T      True if the time in hours is equal to n.
2145              t      True if the time in minutes is equal to n.
2146              v      True if the array psvar has at least n elements.
2147              V      True  if  element  n  of  the  array  psvar  is  set  and
2148                     non-empty.
2149              w      True if the day of the week is equal to n (Sunday = 0).
2150
2151       %<string<
2152       %>string>
2153       %[xstring]
2154              Specifies  truncation  behaviour for the remainder of the prompt
2155              string.   The  third,  deprecated,   form   is   equivalent   to
2156              `%xstringx',  i.e. x may be `<' or `>'.  The string will be dis‐
2157              played in place of the truncated portion  of  any  string;  note
2158              this does not undergo prompt expansion.
2159
2160              The numeric argument, which in the third form may appear immedi‐
2161              ately after the `[', specifies the maximum permitted  length  of
2162              the various strings that can be displayed in the prompt.  In the
2163              first two forms, this numeric argument may be negative, in which
2164              case  the truncation length is determined by subtracting the ab‐
2165              solute value of the numeric argument from the number of  charac‐
2166              ter positions remaining on the current prompt line.  If this re‐
2167              sults in a zero or negative length, a length of 1 is  used.   In
2168              other  words, a negative argument arranges that after truncation
2169              at least n characters remain before the right margin (left  mar‐
2170              gin for RPROMPT).
2171
2172              The  forms  with `<' truncate at the left of the string, and the
2173              forms with `>' truncate at the right of the string.   For  exam‐
2174              ple,  if  the  current  directory  is  `/home/pike',  the prompt
2175              `%8<..<%/' will expand to `..e/pike'.  In this string, the  ter‐
2176              minating  character (`<', `>' or `]'), or in fact any character,
2177              may be quoted by a preceding `\'; note when using print -P, how‐
2178              ever, that this must be doubled as the string is also subject to
2179              standard print processing, in addition to  any  backslashes  re‐
2180              moved  by  a  double quoted string:  the worst case is therefore
2181              `print -P "%<\\\\<<..."'.
2182
2183              If the string is longer than the specified truncation length, it
2184              will appear in full, completely replacing the truncated string.
2185
2186              The part of the prompt string to be truncated runs to the end of
2187              the string, or to the end of the next  enclosing  group  of  the
2188              `%('  construct,  or  to  the next truncation encountered at the
2189              same grouping level (i.e. truncations inside a  `%('  are  sepa‐
2190              rate), which ever comes first.  In particular, a truncation with
2191              argument zero (e.g., `%<<') marks the end of the  range  of  the
2192              string  to  be truncated while turning off truncation from there
2193              on. For example, the prompt  `%10<...<%~%<<%#  '  will  print  a
2194              truncated representation of the current directory, followed by a
2195              `%' or `#', followed by a space.  Without the `%<<',  those  two
2196              characters  would  be  included  in  the string to be truncated.
2197              Note that `%-0<<' is not equivalent to `%<<' but specifies  that
2198              the prompt is truncated at the right margin.
2199
2200              Truncation  applies  only  within  each  individual  line of the
2201              prompt, as delimited by embedded newlines (if any).  If the  to‐
2202              tal length of any line of the prompt after truncation is greater
2203              than the terminal width, or if the part to be truncated contains
2204              embedded  newlines,  truncation  behavior  is  undefined and may
2205              change   in   a   future   version   of    the    shell.     Use
2206              `%-n(l.true-text.false-text)' to remove parts of the prompt when
2207              the available space is less than n.
2208
2209
2210
2211zsh 5.8.1                      February 12, 2022                    ZSHMISC(1)
Impressum