man pages section 1: User Commands

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Updated: July 2014

zshmisc (1)


zshmisc - everything and then some


Please see following description for synopsis


User Commands                                          ZSHMISC(1)

     zshmisc - everything and then some

     A simple command is a sequence of optional parameter assign-
     ments followed by blank-separated words, with optional redi-
     rections  interspersed.  The first word is the command to be
     executed, and the remaining words, if any, are arguments  to
     the  command.   If  a  command  name is given, the parameter
     assignments modify the environment of the command when it is
     executed.  The value of a simple command is its exit status,
     or 128 plus the signal number if  terminated  by  a  signal.
     For example,

          echo foo

     is a simple command with arguments.

     A  pipeline is either a simple command, or a sequence of two
     or more simple commands where each command is separated from
     the  next  by  `|' or `|&'.  Where commands are separated by
     `|', the standard output of the first command  is  connected
     to  the  standard  input of the next.  `|&' is shorthand for
     `2>&1 |', which connects both the standard  output  and  the
     standard  error  of the command to the standard input of the
     next.  The value of a pipeline is the value of the last com-
     mand,  unless  the pipeline is preceded by `!' in which case
     the value is the logical inverse of the value  of  the  last
     command.  For example,

          echo foo | sed 's/foo/bar/'

     is  a  pipeline,  where the output (`foo' plus a newline) of
     the first command will be passed to the input of the second.

     If  a  pipeline is preceded by `coproc', it is executed as a
     coprocess; a two-way pipe is established between it and  the
     parent  shell.   The  shell  can  read  from or write to the
     coprocess by means of the `>&p' and `<&p' redirection opera-
     tors or with `print -p' and `read -p'.  A pipeline cannot be
     preceded by both  `coproc'  and  `!'.   If  job  control  is
     active, the coprocess can be treated in other than input and
     output as an ordinary background job.

     A sublist is either a single pipeline, or a sequence of  two
     or  more  pipelines separated by `&&' or `||'.  If two pipe-
     lines are separated by `&&', the second pipeline is executed
     only  if the first succeeds (returns a zero status).  If two
     pipelines are separated by `||', the second is executed only
     if  the first fails (returns a nonzero status).  Both opera-
     tors have equal precedence and are  left  associative.   The
     value  of  the  sublist  is  the  value of the last pipeline

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     executed.  For example,

          dmesg | grep panic && print yes

     is a sublist consisting of two pipelines, the second just  a
     simple  command  which  will  be executed if and only if the
     grep command returns a zero status.  If  it  does  not,  the
     value  of  the sublist is that return status, else it is the
     status returned by the print (almost certainly zero).

     A list is a sequence of zero or more sublists, in which each
     sublist is terminated by `;', `&', `&|', `&!', or a newline.
     This terminator may optionally be omitted from the last sub-
     list  in the list when the list appears as a complex command
     inside `(...)' or `{...}'.  When a sublist is terminated  by
     `;' or newline, the shell waits for it to finish before exe-
     cuting the next sublist.  If a sublist is  terminated  by  a
     `&',  `&|', or `&!', the shell executes the last pipeline in
     it in the background, and does not wait  for  it  to  finish
     (note  the  difference  from  other shells which execute the
     whole sublist in the background).  A  backgrounded  pipeline
     returns a status of zero.

     More  generally,  a  list  can be seen as a set of any shell
     commands whatsoever, including the complex  commands  below;
     this  is  implied  wherever the word `list' appears in later
     descriptions.  For example, the commands in a shell function
     form a special sort of list.

     A  simple  command may be preceded by a precommand modifier,
     which will alter how the command is interpreted.  These mod-
     ifiers  are  shell  builtin  commands  with the exception of
     nocorrect which is a reserved word.

     -    The command is executed with a  `-'  prepended  to  its
          argv[0] string.

          The  command  word is taken to be the name of a builtin
          command, rather than a shell function or external  com-

     command [ -pvV ]
          The command word is taken to be the name of an external
          command, rather than a shell function or builtin.    If
          the POSIX_BUILTINS option is set, builtins will also be
          executed but certain special  properties  of  them  are
          suppressed.  The  -p  flag  causes a default path to be
          searched instead of that in $path. With  the  -v  flag,
          command is similar to whence and with -V, it is equiva-
          lent to whence -v.

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     exec [ -cl ] [ -a argv0 ]
          The following command together with  any  arguments  is
          run  in  place of the current process, rather than as a
          sub-process.  The shell does not fork and is  replaced.
          The  shell does not invoke TRAPEXIT, nor does it source
          zlogout files.  The options are provided  for  compati-
          bility with other shells.

          The -c option clears the environment.

          The  -l  option is equivalent to the - precommand modi-
          fier, to treat  the  replacement  command  as  a  login
          shell;  the  command  is executed with a - prepended to
          its argv[0] string.  This flag has no  effect  if  used
          together with the -a option.

          The -a option is used to specify explicitly the argv[0]
          string (the name of the command as seen by the  process
          itself)  to  be  used by the replacement command and is
          directly equivalent to setting a value  for  the  ARGV0
          environment variable.

          Spelling  correction  is  not done on any of the words.
          This must appear before any other precommand  modifier,
          as it is interpreted immediately, before any parsing is
          done.  It has no effect in non-interactive shells.

          Filename generation (globbing) is not performed on  any
          of the words.

     A complex command in zsh is one of the following:

     if list then list [ elif list then list ] ... [ else list ]
          The if list is executed, and if it returns a zero  exit
          status, the then list is executed.  Otherwise, the elif
          list is executed and if its status is  zero,  the  then
          list  is  executed.   If each elif list returns nonzero
          status, the else list is executed.

     for name ... [ in word ... ] term do list done
          where term is at least one newline or  ;.   Expand  the
          list  of  words,  and set the parameter name to each of
          them in turn, executing list each time.  If the in word
          is  omitted,  use  the positional parameters instead of
          the words.

          More than one parameter name can appear before the list
          of words.  If N names are given, then on each execution

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          of the loop the next N words are assigned to the corre-
          sponding  parameters.   If  there  are  more names than
          remaining words, the remaining parameters are each  set
          to  the  empty string.  Execution of the loop ends when
          there is no remaining word to assign to the first name.
          It  is only possible for in to appear as the first name
          in the list, else it will be treated as marking the end
          of the list.

     for (( [expr1] ; [expr2] ; [expr3] )) do list done
          The arithmetic expression expr1 is evaluated first (see
          the section `Arithmetic Evaluation').   The  arithmetic
          expression expr2 is repeatedly evaluated until it eval-
          uates to zero and when non-zero, list is  executed  and
          the  arithmetic  expression  expr3  evaluated.   If any
          expression is omitted, then it behaves as if it  evalu-
          ated to 1.

     while list do list done
          Execute the do list as long as the while list returns a
          zero exit status.

     until list do list done
          Execute the do list as long as  until  list  returns  a
          nonzero exit status.

     repeat word do list done
          word  is  expanded and treated as an arithmetic expres-
          sion, which must evaluate to a number n.  list is  then
          executed n times.

          The repeat syntax is disabled by default when the shell
          starts in a mode emulating another shell.   It  can  be
          enabled with the command `enable -r repeat'

... esac
     case  word in [ [(] pattern [ | pattern ] ... ) list
          (;;|;&|;|) ]
          Execute the list associated with the first pattern that
          matches word, if any.  The form of the patterns is  the
          same  as  that  used  for filename generation.  See the
          section `Filename Generation'.

          If the list that is  executed  is  terminated  with  ;&
          rather  than  ;;,  the following list is also executed.
          The rule for the terminator of the following  list  ;;,
          ;& or ;| is applied unless the esac is reached.

          If  the list that is executed is terminated with ;| the
          shell continues to scan the patterns  looking  for  the
          next  match,  executing  the  corresponding  list,  and
          applying the rule for the corresponding terminator  ;;,

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          ;&  or  ;|.   Note  that  word  is not re-expanded; all
          applicable patterns are tested with the same word.

     select name [ in word ... term ] do list done
          where term is one or more newline or ; to terminate the
          words.  Print the set of words, each preceded by a num-
          ber.  If the in word is  omitted,  use  the  positional
          parameters.   The  PROMPT3 prompt is printed and a line
          is read from the line editor if the shell  is  interac-
          tive  and  that  is active, or else standard input.  If
          this line consists of the number of one of  the  listed
          words,  then the parameter name is set to the word cor-
          responding to this number.  If this line is empty,  the
          selection  list is printed again.  Otherwise, the value
          of the parameter name is set to null.  The contents  of
          the  line  read  from  standard  input  is saved in the
          parameter REPLY.  list is executed for  each  selection
          until a break or end-of-file is encountered.

     ( list )
          Execute  list  in  a  subshell.   Traps set by the trap
          builtin are reset to their default values while execut-
          ing list.

     { list }
          Execute list.

     { try-list } always { always-list }
          First  execute  try-list.   Regardless  of  errors,  or
          break, continue, or return commands encountered  within
          try-list,  execute always-list.  Execution then contin-
          ues from the result of the execution  of  try-list;  in
          other  words,  any error, or break, continue, or return
          command is treated in the normal way, as if always-list
          were  not present.  The two chunks of code are referred
          to as the `try block' and the `always block'.

          Optional newlines or semicolons may  appear  after  the
          always; note, however, that they may not appear between
          the preceding closing brace and the always.

          An `error' in this context is a  condition  such  as  a
          syntax  error which causes the shell to abort execution
          of the  current  function,  script,  or  list.   Syntax
          errors  encountered while the shell is parsing the code
          do not cause the always-list to be executed.  For exam-
          ple,  an  erroneously  constructed if block in try-list
          would cause the shell to abort during parsing, so  that
          always-list  would  not be executed, while an erroneous
          substitution such as ${*foo*} would  cause  a  run-time
          error, after which always-list would be executed.

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          An  error  condition  can  be tested and reset with the
          special integer variable TRY_BLOCK_ERROR.   Outside  an
          always-list  the  value  is  irrelevant, but it is ini-
          tialised to -1.  Inside always-list, the value is 1  if
          an   error  occurred  in  the  try-list,  else  0.   If
          TRY_BLOCK_ERROR is set to 0 during the always-list, the
          error  condition  caused  by the try-list is reset, and
          shell execution continues normally  after  the  end  of
          always-list.  Altering the value during the try-list is
          not useful (unless this  forms  part  of  an  enclosing
          always block).

          Regardless   of   TRY_BLOCK_ERROR,  after  the  end  of
          always-list the normal shell status  $?  is  the  value
          returned  from  always-list.   This will be non-zero if
          there was an error, even if TRY_BLOCK_ERROR was set  to

          The  following  executes  the  given code, ignoring any
          errors it causes.  This is an alternative to the  usual
          convention of protecting code by executing it in a sub-

                   # code which may cause an error
                 } always {
                   # This code is executed regardless of the error.
                   (( TRY_BLOCK_ERROR = 0 ))
               # The error condition has been reset.

          An exit command (or a return command  executed  at  the
          outermost  function  level  of a script) encountered in
          try-list does not cause the execution  of  always-list.
          Instead,  the  shell  exits  immediately after any EXIT
          trap has been executed.

     function word ... [ () ] [ term ] { list }
     word ... () [ term ] { list }
     word ... () [ term ] command
          where term is one or more newline or ;.  Define a func-
          tion which is referenced by any one of word.  Normally,
          only one word is provided; multiple words  are  usually
          only  useful  for setting traps.  The body of the func-
          tion is the list between the { and }.  See the  section

          If  the  option  SH_GLOB  is set for compatibility with
          other  shells,  then  whitespace  may  appear   between
          between  the left and right parentheses when there is a
          single  word;   otherwise,  the  parentheses  will   be
          treated as forming a globbing pattern in that case.

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     time [ pipeline ]
          The  pipeline  is  executed,  and timing statistics are
          reported on the standard error in the form specified by
          the  TIMEFMT  parameter.  If pipeline is omitted, print
          statistics about the shell process and its children.

     [[ exp ]]
          Evaluates the conditional expression exp and  return  a
          zero  exit status if it is true.  See the section `Con-
          ditional Expressions' for a description of exp.

     Many of zsh's complex commands have alternate forms.   These
     are  non-standard  and  are likely not to be obvious even to
     seasoned shell programmers; they should not be used anywhere
     that portability of shell code is a concern.

     The short versions below only work if sublist is of the form
     `{ list }' or if the SHORT_LOOPS option is set.  For the if,
     while  and until commands, in both these cases the test part
     of the loop must also be suitably delimited, such as by  `[[
     ... ]]' or `(( ... ))', else the end of the test will not be
     recognized.  For the for, repeat, case and  select  commands
     no such special form for the arguments is necessary, but the
     other condition (the special form of sublist or use  of  the
     SHORT_LOOPS option) still applies.

     if list { list } [ elif list { list } ] ... [ else { list }
          An alternate form of if.  The rules mean that

               if [[ -o ignorebraces ]] {
                 print yes

          works, but

               if true {  # Does not work!
                 print yes

          does not, since the test is not suitably delimited.

     if list sublist
          A short form of the alternate `if'.  The  same  limita-
          tions  on  the  form  of list apply as for the previous

     for name ... ( word ... ) sublist
          A short form of for.

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     for name ... [ in word ... ] term sublist
          where term is at least one newline or ;.  Another short
          form of for.

     for (( [expr1] ; [expr2] ; [expr3] )) sublist
          A short form of the arithmetic for command.

     foreach name ... ( word ... ) list end
          Another form of for.

     while list { list }
          An  alternative form of while.  Note the limitations on
          the form of list mentioned above.

     until list { list }
          An alternative form of until.  Note the limitations  on
          the form of list mentioned above.

     repeat word sublist
          This is a short form of repeat.

... }
     case  word  { [ [(] pattern [ | pattern ] ... ) list
          (;;|;&|;|) ]
          An alternative form of case.

     select name [ in word term ] sublist
          where  term is at least one newline or ;.  A short form
          of select.

     The following words are recognized as  reserved  words  when
     used  as  the  first word of a command unless quoted or dis-
     abled using disable -r:

     do done esac then elif else fi for case  if  while  function
     repeat time until select coproc nocorrect foreach end ! [[ {

     Additionally, `}' is recognized in any position  if  neither
     the  IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option
     is set.

     Certain errors are treated as fatal  by  the  shell:  in  an
     interactive  shell, they cause control to return to the com-
     mand line, and in a non-interactive  shell  they  cause  the
     shell to be aborted.  In older versions of zsh, a non-inter-
     active shell running a script would  not  abort  completely,
     but  would  resume  execution at the next command to be read
     from the script, skipping the remainder of any functions  or
     shell  constructs such as loops or conditions; this somewhat

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     illogical behaviour can be recovered by setting  the  option

     Fatal errors found in non-interactive shells include:
     Failure to parse shell options passed when invoking the
     Failure to change options with the set builtin
     Parse errors of all sorts, including failures to parse
          mathematical expressions
     Failures to set or modify variable behaviour with typeset,
          local, declare, export, integer, float
     Execution of incorrectly positioned loop control structures
          (continue, break)
     Attempts to use regular expression with no regular expres-
          module available
     Disallowed operations when the RESTRICTED options is set
     Failure to create a pipe needed for a pipeline
     Failure to create a multio
     Failure to autoload a module needed for a declared shell
     Errors creating command or process substitutions
     Syntax errors in glob qualifiers
     File generation errors where not caught by the option
     All bad patterns used for matching within case statements
     File generation failures where not caused by NO_MATCH or
     All file generation errors where the pattern was used to
          create a
     Memory errors where detected by the shell
     Invalid subscripts to shell variables
     Attempts to assign read-only variables
     Logical errors with variables such as  assignment  to  the
     Use of invalid variable names
     Errors in variable substitution syntax
     Failure to convert characters in $'...' expressions
          similar options

     If the POSIX_BUILTINS option is set, more errors  associated
     with  shell builtin commands are treated as fatal, as speci-
     fied by the POSIX standard.

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

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     Every token in the shell input is checked to see if there is
     an  alias defined for it.  If so, it is replaced by the text
     of the alias if it is in command position (if  it  could  be
     the  first  word  of  a  simple command), or if the alias is
     global.  If the text ends with a space, the next word in the
     shell input is treated as though it were in command position
     for purposes of alias expansion.  An alias is defined  using
     the  alias  builtin; global aliases may be defined using the
     -g option to that builtin.

     Alias expansion is done on the shell input before any  other
     expansion  except history expansion.  Therefore, if an alias
     is defined for the word foo, alias expansion may be  avoided
     by quoting part of the word, e.g. \foo.  Any form of quoting
     works, although there is nothing to prevent an  alias  being
     defined  for  the quoted form such as \foo as well.  For use
     with completion, which would  remove  an  initial  backslash
     followed  by  a character that isn't special, it may be more
     convenient to quote the  word  by  starting  with  a  single
     quote,  i.e.  'foo;  completion  will  automatically add the
     trailing single quote.

     There is a commonly encountered problem with aliases  illus-
     trated by the following code:

          alias echobar='echo bar'; echobar

     This  prints a message that the command echobar could not be
     found.  This happens because aliases are expanded  when  the
     code  is read in; the entire line is read in one go, so that
     when echobar is executed it is too late to expand the  newly
     defined  alias.   This  is often a problem in shell scripts,
     functions, and code executed with `source' or  `.'.   Conse-
     quently, use of functions rather than aliases is recommended
     in non-interactive code.

     Note also the unhelpful interaction of aliases and  function

          alias func='noglob func'
          func() {
              echo Do something with $*

     Because  aliases  are expanded in function definitions, this
     causes the following command to be executed:

          noglob func() {
              echo Do something with $*

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     which defines noglob as well as func as functions  with  the
     body  given.   To  avoid this, either quote the name func or
     use  the  alternative  function  definition  form  `function
     func'.   Ensuring  the  alias  is defined after the function
     works but is problematic  if  the  code  fragment  might  be

     A  character  may  be  quoted  (that  is,  made to stand for
     itself) by preceding it with a `\'.  `\' followed by a  new-
     line is ignored.

     A string enclosed between `$'' and `'' is processed the same
     way as the string arguments of the print  builtin,  and  the
     resulting  string  is  considered  to be entirely quoted.  A
     literal `'' character can be included in the string by using
     the `\'' escape.

     All characters enclosed between a pair of single quotes ('')
     that is not preceded by a `$' are quoted.   A  single  quote
     cannot   appear  within  single  quotes  unless  the  option
     RC_QUOTES is set, in which case a pair of single quotes  are
     turned into a single quote.  For example,

          print ''''

     outputs  nothing  apart  from  a newline if RC_QUOTES is not
     set, but one single quote if it is set.

     Inside double quotes (""), parameter and  command  substitu-
     tion occur, and `\' quotes the characters `\', ``', `"', and

     If a command is followed by & and job control is not active,
     then the default standard input for the command is the empty
     file /dev/null.  Otherwise, the environment for  the  execu-
     tion  of  a  command  contains  the  file descriptors of the
     invoking shell as modified by input/output specifications.

     The following may appear anywhere in a simple command or may
     precede  or  follow  a  complex  command.   Expansion occurs
     before word or digit is used except as noted below.  If  the
     result  of substitution on word produces more than one file-
     name, redirection occurs for each separate filename in turn.

     < word
          Open file word for reading as standard input.

     <> word
          Open  file  word  for  reading  and writing as standard
          input.  If the file does not exist then it is  created.

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     > word
          Open  file word for writing as standard output.  If the
          file does not exist then it is created.   If  the  file
          exists, and the CLOBBER option is unset, this causes an
          error; otherwise, it is truncated to zero length.

     >| word
     >! word
          Same as >, except that the file is  truncated  to  zero
          length if it exists, even if CLOBBER is unset.

     >> word
          Open  file  word for writing in append mode as standard
          output.  If the file does not exist,  and  the  CLOBBER
          option  is  unset, this causes an error; otherwise, the
          file is created.

     >>| word
     >>! word
          Same as >>, except that the file is created if it  does
          not exist, even if CLOBBER is unset.

     <<[-] word
          The  shell  input is read up to a line that is the same
          as word, or to an end-of-file.  No parameter expansion,
          command  substitution  or  filename  generation is per-
          formed on  word.   The  resulting  document,  called  a
          here-document, becomes the standard input.

          If  any character of word is quoted with single or dou-
          ble quotes or a `\', no interpretation is  placed  upon
          the  characters  of the document.  Otherwise, parameter
          and command substitution occurs, `\' followed by a new-
          line  is  removed,  and  `\'  must be used to quote the
          characters `\', `$', ``' and  the  first  character  of

          Note that word itself does not undergo shell expansion.
          Backquotes in word do  not  have  their  usual  effect;
          instead  they behave similarly to double quotes, except
          that  the  backquotes  themselves  are  passed  through
          unchanged.  (This information is given for completeness
          and it is not recommended  that  backquotes  be  used.)
          Quotes in the form $'...' have their standard effect of
          expanding backslashed references to special characters.

          If <<- is used, then all leading tabs are stripped from
          word and from the document.

     <<< word
          Perform shell expansion on word and pass the result  to
          standard  input.   This  is  known  as  a  here-string.

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          Compare the use of word in here-documents above,  where
          word does not undergo shell expansion.

     <& number
     >& number
          The  standard  input/output  is  duplicated  from  file
          descriptor number (see dup2(2)).

     <& -
     >& - Close the standard input/output.

     <& p
     >& p The input/output from/to the coprocess is moved to  the
          standard input/output.

     >& word
     &> word
          (Except  where  `>& word' matches one of the above syn-
          taxes; `&>' can always be used to  avoid  this  ambigu-
          ity.)   Redirects  both  standard  output  and standard
          error (file descriptor 2) in the manner  of  `>  word'.
          Note that this does not have the same effect as `> word
          2>&1' in the  presence  of  multios  (see  the  section

     >&| word
     >&! word
     &>| word
     &>! word
          Redirects both standard output and standard error (file
          descriptor 2) in the manner of `>| word'.

     >>& word
     &>> word
          Redirects both standard output and standard error (file
          descriptor 2) in the manner of `>> word'.

     >>&| word
     >>&! word
     &>>| word
     &>>! word
          Redirects both standard output and standard error (file
          descriptor 2) in the manner of `>>| word'.

     If one of the above is preceded by a digit,  then  the  file
     descriptor  referred  to  is  that  specified  by  the digit
     instead of the default 0 or 1.  The order in which  redirec-
     tions  are  specified  is  significant.  The shell evaluates
     each redirection in terms of  the  (file  descriptor,  file)
     association at the time of evaluation.  For example:

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User Commands                                          ZSHMISC(1)

          ... 1>fname 2>&1

     first associates file descriptor 1 with file fname.  It then
     associates file descriptor 2 with the file  associated  with
     file  descriptor  1 (that is, fname).  If the order of redi-
     rections were reversed, file descriptor 2 would  be  associ-
     ated with the terminal (assuming file descriptor 1 had been)
     and then file descriptor 1 would  be  associated  with  file

     The  `|&'  command  separator described in Simple Commands &
     Pipelines in zshmisc(1) is a shorthand for `2>&1 |'.

     The various forms of process  substitution,  `<(list)',  and
     `=(list())'  for  input  and `>(list)' for output, are often
     used together with redirection.  For example, if word in  an
     output  redirection is of the form `>(list)' then the output
     is piped to the command represented by  list.   See  Process
     Substitution in zshexpn(1).

     When  the  shell  is parsing arguments to a command, and the
     shell option IGNORE_BRACES is not set, a different  form  of
     redirection is allowed: instead of a digit before the opera-
     tor there is a valid shell identifier  enclosed  in  braces.
     The shell will open a new file descriptor that is guaranteed
     to be at least 10 and set the parameter named by the identi-
     fier  to  the  file  descriptor  opened.   No  whitespace is
     allowed between the closing brace and the redirection  char-
     acter.  For example:

          ... {myfd}>&1

     This opens a new file descriptor that is a duplicate of file
     descriptor 1 and sets the parameter myfd to  the  number  of
     the  file  descriptor,  which  will be at least 10.  The new
     file descriptor can be written to using the syntax  >&$myfd.

     The syntax {varid}>&-, for example {myfd}>&-, may be used to
     close a file descriptor opened in this fashion.   Note  that
     the  parameter  given  by  varid must previously be set to a
     file descriptor in this case.

     It is an error to open or close a file  descriptor  in  this
     fashion  when the parameter is readonly.  However, it is not
     an error to read or write a file descriptor  using  <&$param
     or >&$param if param is readonly.

     If  the  option  CLOBBER  is unset, it is an error to open a
     file descriptor using a parameter that is already set to  an
     open file descriptor previously allocated by this mechanism.
     Unsetting the parameter before using  it  for  allocating  a

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     file descriptor avoids the error.

     Note  that  this mechanism merely allocates or closes a file
     descriptor; it does not perform any redirections from or  to
     it.   It is usually convenient to allocate a file descriptor
     prior to use as an argument to exec.  The syntax does not in
     any  case  work  when  used  around complex commands such as
     parenthesised subshells or loops, where the opening brace is
     interpreted  as part of a command list to be executed in the
     current shell.

     The following shows a typical sequence of  allocation,  use,
     and closing of a file descriptor:

          integer myfd
          exec {myfd}>~/logs/mylogfile.txt
          print This is a log message. >&$myfd
          exec {myfd}>&-

     Note  that  the  expansion of the variable in the expression
     >&$myfd occurs at the point the redirection is opened.  This
     is  after  the  expansion of command arguments and after any
     redirections to the left on the command line have been  pro-

     If the user tries to open a file descriptor for writing more
     than once, the shell opens the file descriptor as a pipe  to
     a  process  that  copies its input to all the specified out-
     puts, similar to tee, provided the MULTIOS option is set, as
     it is by default.  Thus:

          date >foo >bar

     writes  the  date to two files, named `foo' and `bar'.  Note
     that a pipe is an implicit redirection; thus

          date >foo | cat

     writes the date to the file `foo', and also pipes it to cat.

     If  the  MULTIOS option is set, the word after a redirection
     operator is also subjected  to  filename  generation  (glob-
     bing).  Thus

          : > *

     will  truncate  all files in the current directory, assuming
     there's at least one.  (Without the MULTIOS option, it would
     create an empty file called `*'.)  Similarly, you can do

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          echo exit 0 >> *.sh

     If the user tries to open a file descriptor for reading more
     than once, the shell opens the file descriptor as a pipe  to
     a process that copies all the specified inputs to its output
     in the order specified, similar to cat, provided the MULTIOS
     option is set.  Thus

          sort <foo <fubar

     or even

          sort <f{oo,ubar}

     is equivalent to `cat foo fubar | sort'.

     Expansion  of  the  redirection argument occurs at the point
     the redirection is opened, at the point described above  for
     the expansion of the variable in >&$myfd.

     Note that a pipe is an implicit redirection; thus

          cat bar | sort <foo

     is equivalent to `cat bar foo | sort' (note the order of the

     If the MULTIOS option is unset,  each  redirection  replaces
     the previous redirection for that file descriptor.  However,
     all files redirected to are actually opened, so

          echo foo > bar > baz

     when MULTIOS is unset will truncate  bar,  and  write  `foo'
     into baz.

     There  is  a problem when an output multio is attached to an
     external program.  A simple example shows this:

          cat file >file1 >file2
          cat file1 file2

     Here, it is possible that the second `cat' will not  display
     the full contents of file1 and file2 (i.e. the original con-
     tents of file repeated twice).

     The reason for this is that the multios  are  spawned  after
     the cat process is forked from the parent shell, so the par-
     ent shell does not wait for the multios  to  finish  writing
     data.  This means the command as shown can exit before file1
     and file2 are completely written.  As a  workaround,  it  is
     possible  to  run  the  cat  process as part of a job in the

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     current shell:

          { cat file } >file >file2

     Here, the {...} job will pause to wait for both files to  be

     When  a  simple  command consists of one or more redirection
     operators and zero or more  parameter  assignments,  but  no
     command name, zsh can behave in several ways.

     If  the parameter NULLCMD is not set or the option CSH_NULL-
     CMD is set, an error is caused.  This is  the  csh  behavior
     and CSH_NULLCMD is set by default when emulating csh.

     If the option SH_NULLCMD is set, the builtin `:' is inserted
     as a command with  the  given  redirections.   This  is  the
     default when emulating sh or ksh.

     Otherwise,  if  the parameter NULLCMD is set, its value will
     be used as a command with the given redirections.   If  both
     NULLCMD  and READNULLCMD are set, then the value of the lat-
     ter will be used instead of that of the former when the  re-
     direction is an input.  The default for NULLCMD is `cat' and
     for READNULLCMD is `more'. Thus

          < file

     shows the contents of file on standard output,  with  paging
     if that is a terminal.  NULLCMD and READNULLCMD may refer to
     shell functions.

     If a command name contains no slashes, the shell attempts to
     locate  it.   If there exists a shell function by that name,
     the function is invoked as described in the  section  `Func-
     tions'.   If  there exists a shell builtin by that name, the
     builtin is invoked.

     Otherwise, the shell searches each element of  $path  for  a
     directory  containing  an  executable file by that name.  If
     the search is unsuccessful, the shell prints an  error  mes-
     sage and returns a nonzero exit status.

     If  execution  fails  because  the file is not in executable
     format, and the file is not a directory, it is assumed to be
     a  shell  script.  /bin/sh is spawned to execute it.  If the
     program is a file beginning with `#!', the remainder of  the
     first  line  specifies  an interpreter for the program.  The
     shell will execute the specified  interpreter  on  operating
     systems  that  do  not  handle this executable format in the

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     If  no  external  command  is  found  but  a  function  com-
     mand_not_found_handler  exists the shell executes this func-
     tion with all command line arguments.  The  function  should
     return  status  zero if it successfully handled the command,
     or non-zero status if it failed.  In  the  latter  case  the
     standard handling is applied: `command not found' is printed
     to standard error and the shell exits with status 127.  Note
     that the handler is executed in a subshell forked to execute
     an external command, hence  changes  to  directories,  shell
     parameters, etc. have no effect on the main shell.

     Shell  functions are defined with the function reserved word
     or the special syntax `funcname ()'.   Shell  functions  are
     read  in  and  stored  internally.  Alias names are resolved
     when the function is read.  Functions are executed like com-
     mands  with  the  arguments passed as positional parameters.
     (See the section `Command Execution'.)

     Functions execute in the same  process  as  the  caller  and
     share  all  files  and  present  working  directory with the
     caller.  A trap on EXIT set inside a  function  is  executed
     after  the  function  completes  in  the  environment of the

     The return builtin is used to return from function calls.

     Function  identifiers  can  be  listed  with  the  functions
     builtin.   Functions  can  be  undefined with the unfunction

     A function can be marked as  undefined  using  the  autoload
     builtin  (or `functions -u' or `typeset -fu').  Such a func-
     tion has no body.  When the function is first executed,  the
     shell  searches for its definition using the elements of the
     fpath variable.  Thus to define functions for autoloading, a
     typical sequence is:

          fpath=(~/myfuncs $fpath)
          autoload myfunc1 myfunc2 ...

     The  usual alias expansion during reading will be suppressed
     if the autoload builtin  or  its  equivalent  is  given  the
     option -U. This is recommended for the use of functions sup-
     plied with the zsh distribution.  Note  that  for  functions
     precompiled  with  the  zcompile builtin command the flag -U
     must be provided when the .zwc file is created, as the  cor-
     responding information is compiled into the latter.

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     For  each element in fpath, the shell looks for three possi-
     ble files, the newest of which is used to load  the  defini-
     tion for the function:

          A file created with the zcompile builtin command, which
          is expected to contain the definitions  for  all  func-
          tions  in  the  directory  named  element.  The file is
          treated in the same manner as  a  directory  containing
          files  for functions and is searched for the definition
          of the function.   If the definition is not found,  the
          search  for  a  definition  proceeds with the other two
          possibilities described below.

          If element already includes a .zwc extension (i.e.  the
          extension was explicitly given by the user), element is
          searched for the definition  of  the  function  without
          comparing  its  age  to  that  of other files; in fact,
          there does not need to be any directory  named  element
          without  the suffix.  Thus including an element such as
          `/usr/local/funcs.zwc'  in  fpath  will  speed  up  the
          search  for functions, with the disadvantage that func-
          tions included must be explicitly  recompiled  by  hand
          before the shell notices any changes.

          A file created with zcompile, which is expected to con-
          tain the definition for function.  It may include other
          function  definitions  as  well,  but those are neither
          loaded nor executed;  a  file  found  in  this  way  is
          searched only for the definition of function.

          A  file of zsh command text, taken to be the definition
          for function.

     In summary, the order of searching is, first, in the parents
     of  directories  in fpath for the newer of either a compiled
     directory or a directory in fpath; second, if more than  one
     of  these  contains  a  definition  for the function that is
     sought, the leftmost in the  fpath  is  chosen;  and  third,
     within  a directory, the newer of either a compiled function
     or an ordinary function definition is used.

     If the KSH_AUTOLOAD option is set, or the file contains only
     a  simple  definition  of  the function, the file's contents
     will be executed.  This will normally define the function in
     question, but may also perform initialization, which is exe-
     cuted in the context of  the  function  execution,  and  may
     therefore  define  local  parameters.  It is an error if the
     function is not defined by loading the file.

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     Otherwise, the function body  (with  no  surrounding  `func-
     name()  {...}')  is taken to be the complete contents of the
     file.  This form allows the file to be used directly  as  an
     executable  shell script.  If processing of the file results
     in the function being re-defined, the function itself is not
     re-executed.   To  force the shell to perform initialization
     and then call the function defined, the file should  contain
     initialization  code (which will be executed then discarded)
     in addition to a complete function definition (which will be
     retained  for  subsequent calls to the function), and a call
     to the shell function, including any arguments, at the  end.

     For example, suppose the autoload file func contains

          func() { print This is func; }
          print func is initialized

     then  `func;  func'  with KSH_AUTOLOAD set will produce both
     messages on the first call, but only the  message  `This  is
     func'   on   the   second  and  subsequent  calls.   Without
     KSH_AUTOLOAD set, it will produce the initialization message
     on  the  first call, and the other message on the second and
     subsequent calls.

     It is also possible to create a function that is not  marked
     as autoloaded, but which loads its own definition by search-
     ing fpath, by using `autoload -X' within a  shell  function.
     For example, the following are equivalent:

          myfunc() {
            autoload -X
          myfunc args...


          unfunction myfunc   # if myfunc was defined
          autoload myfunc
          myfunc args...

     In fact, the functions command outputs `builtin autoload -X'
     as the body of an autoloaded function.  This is done so that

          eval "$(functions)"

     produces  a  reasonable  result.  A true autoloaded function
     can be identified by the presence of the  comment  `#  unde-
     fined'  in the body, because all comments are discarded from
     defined functions.

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     To load the definition  of  an  autoloaded  function  myfunc
     without executing myfunc, use:

          autoload +X myfunc

     If no name is given for a function, it is `anonymous' and is
     handled specially.  Either form of function  definition  may
     be used: a `()' with no preceding name, or a `function' with
     an immediately following open brace.  The function  is  exe-
     cuted  immediately  at  the  point  of definition and is not
     stored  for  future  use.   The  function  name  is  set  to

     Arguments  to the function may be specified as words follow-
     ing the closing brace defining the function, hence if  there
     are  none  no  arguments (other than $0) are set.  This is a
     difference from the way other functions are  parsed:  normal
     function  definitions  may  be  followed by certain keywords
     such as `else' or `fi', which will be treated  as  arguments
     to  anonymous  functions,  so that a newline or semicolon is
     needed to force keyword interpretation.

     Note also that the argument list of any enclosing script  or
     function is hidden (as would be the case for any other func-
     tion called at this point).

     Redirections may be applied to the anonymous function in the
     same  manner  as  to  a  current-shell structure enclosed in
     braces.  The main use of anonymous functions is to provide a
     scope  for local variables.  This is particularly convenient
     in start-up files as these do not provide  their  own  local
     variable scope.

     For example,

          function {
            local variable=inside
            print "I am $variable with arguments $*"
          } this and that
          print "I am $variable"

     outputs the following:

          I am inside with arguments this and that
          I am outside

     Note that function definitions with arguments that expand to
     nothing, for example `name=; function $name {  ...  }',  are
     not  treated  as  anonymous  functions.   Instead,  they are
     treated as normal function definitions where the  definition

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     is silently discarded.

     Certain  functions,  if defined, have special meaning to the

  Hook Functions
     For the functions below, it is possible to define  an  array
     that  has  the  same  name as the function with `_functions'
     appended.  Any element in such an array is taken as the name
     of a function to execute; it is executed in the same context
     and with the same arguments  as  the  basic  function.   For
     example, if $chpwd_functions is an array containing the val-
     ues  `mychpwd',  `chpwd_save_dirstack',   then   the   shell
     attempts  to  execute  the  functions `chpwd', `mychpwd' and
     `chpwd_save_dirstack', in that  order.   Any  function  that
     does  not  exist  is  silently ignored.  A function found by
     this mechanism is referred to elsewhere  as  a  `hook  func-
     tion'.  An error in any function causes subsequent functions
     not to be run.  Note further that an error in a precmd  hook
     causes an immediately following periodic function not to run
     (though it may run at the next opportunity).

          Executed whenever  the  current  working  directory  is

          If  the  parameter PERIOD is set, this function is exe-
          cuted every $PERIOD  seconds,  just  before  a  prompt.
          Note  that  if multiple functions are defined using the
          array periodic_functions only one period is applied  to
          the  complete  set of functions, and the scheduled time
          is not reset if  the  list  of  functions  is  altered.
          Hence the set of functions is always called together.

          Executed  before  each  prompt.   Note  that precommand
          functions are not re-executed simply because  the  com-
          mand  line  is redrawn, as happens, for example, when a
          notification about an exiting job is displayed.

          Executed just after a command  has  been  read  and  is
          about  to  be  executed.   If  the history mechanism is
          active (and the line was not discarded from the history
          buffer),  the  string  that the user typed is passed as
          the first argument, otherwise it is  an  empty  string.
          The  actual  command  that  will be executed (including
          expanded aliases) is passed in two different forms: the
          second  argument is a single-line, size-limited version
          of  the  command  (with  things  like  function  bodies

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          elided); the third argument contains the full text that
          is being executed.

          Executed when a history line  has  been  read  interac-
          tively,  but  before it is executed.  The sole argument
          is the complete history line (so that  any  terminating
          newline will still be present).

          If  any  of the hook functions returns status 1 (or any
          non-zero value other than 2, though this is not guaran-
          teed for future versions of the shell) the history line
          will not be saved, although it lingers in  the  history
          until  the next line is executed, allowing you to reuse
          or edit it immediately.

          If any of the hook functions returns status 2 the  his-
          tory  line  will be saved on the internal history list,
          but not written to the history file.  In case of a con-
          flict, the first non-zero status value is taken.

          A hook function may call `fc -p ...' to switch the his-
          tory context so that the history is saved in a  differ-
          ent  file  from the that in the global HISTFILE parame-
          ter.  This is handled specially: the history context is
          automatically restored after the processing of the his-
          tory line is finished.

          The following example function works with  one  of  the
          options  INC_APPEND_HISTORY  or  SHARE_HISTORY  set, in
          order that the line is written  out  immediately  after
          the  history entry is added.  It first adds the history
          line to the normal history with the  newline  stripped,
          which  is  usually  the  correct  behaviour.   Then  it
          switches the history context so that the line  will  be
          written to a history file in the current directory.

               zshaddhistory() {
                 print -sr -- ${1%%$'\n'}
                 fc -p .zsh_local_history

          Executed  at the point where the main shell is about to
          exit normally.  This is  not  called  by  exiting  sub-
          shells,  nor  when the exec precommand modifier is used
          before an external command.  Also, unlike TRAPEXIT,  it
          is not called when functions exit.

  Trap Functions
     The  functions  below  are treated specially but do not have
     corresponding hook arrays.

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          If defined and non-null, this function will be executed
          whenever  the  shell catches a signal SIGNAL, where NAL
          is a signal name as specified  for  the  kill  builtin.
          The signal number will be passed as the first parameter
          to the function.

          If a function of this form is  defined  and  null,  the
          shell and processes spawned by it will ignore SIGNAL.

          The  return  status  from  the function is handled spe-
          cially.  If it is zero, the signal is assumed  to  have
          been handled, and execution continues normally.  Other-
          wise, the shell will behave as interrupted except  that
          the return status of the trap is retained.

          Programs   terminated  by  uncaught  signals  typically
          return the status 128 plus the  signal  number.   Hence
          the  following causes the handler for SIGINT to print a
          message, then mimic the usual effect of the signal.

               TRAPINT() {
                 print "Caught SIGINT, aborting."
                 return $(( 128 + $1 ))

          The functions  TRAPZERR,  TRAPDEBUG  and  TRAPEXIT  are
          never executed inside other traps.

          If  the  option  DEBUG_BEFORE_CMD  is  set (as it is by
          default), executed before each command; otherwise  exe-
          cuted  after  each command.  See the description of the
          trap builtin in zshbuiltins(1)  for  details  of  addi-
          tional features provided in debug traps.

          Executed  when  the  shell  exits,  or when the current
          function exits if defined inside a function.  The value
          of  $?  at the start of execution is the exit status of
          the shell or the return status of the function exiting.

          Executed whenever a command has a non-zero exit status.
          However, the function is not executed  if  the  command
          occurred  in  a  sublist followed by `&&' or `||'; only
          the final command in a sublist of this type causes  the
          trap  to  be  executed.   The function TRAPERR acts the
          same as TRAPZERR on systems where there  is  no  SIGERR
          (this is the usual case).

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     The  functions beginning `TRAP' may alternatively be defined
     with the trap builtin:  this  may  be  preferable  for  some
     uses.   Setting a trap with one form removes any trap of the
     other form for the same signal; removing a  trap  in  either
     form removes all traps for the same signal.  The forms

          TRAPNAL() {
           # code

     ('function traps') and

          trap '
           # code
          ' NAL

     ('list  traps')  are equivalent in most ways, the exceptions
     being the following:

     o    Function traps have all the properties of normal  func-
          tions,  appearing  in  the  list of functions and being
          called with their own function context rather than  the
          context where the trap was triggered.

     o    The  return  status  from  function  traps  is special,
          whereas a return from a list trap causes the  surround-
          ing context to return with the given status.

     o    Function  traps  are  not  reset  within  subshells, in
          accordance with zsh behaviour; list traps are reset, in
          accordance with POSIX behaviour.

     If  the  MONITOR  option  is set, an interactive shell asso-
     ciates a job with each pipeline.  It keeps a table  of  cur-
     rent  jobs,  printed  by  the jobs command, and assigns them
     small integer numbers.  When a job is started asynchronously
     with  `&',  the  shell prints a line to standard error which
     looks like:

          [1] 1234

     indicating that the job which was started asynchronously was
     job  number 1 and had one (top-level) process, whose process
     ID was 1234.

     If a job is started with `&|' or  `&!',  then  that  job  is
     immediately  disowned.   After  startup,  it does not have a
     place in the job table, and is not subject to the  job  con-
     trol features described here.

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     If  you  are running a job and wish to do something else you
     may hit the key ^Z (control-Z) which sends a TSTP signal  to
     the  current  job:   this  key  may be redefined by the susp
     option of the external stty command.  The  shell  will  then
     normally  indicate  that  the  job has been `suspended', and
     print another prompt.  You can then manipulate the state  of
     this  job, putting it in the background with the bg command,
     or run some other commands and then eventually bring the job
     back  into the foreground with the foreground command fg.  A
     ^Z takes effect immediately and is like an interrupt in that
     pending  output  and  unread  input are discarded when it is

     A job being run in the background will suspend if  it  tries
     to read from the terminal.

     Note  that  if  the job running in the foreground is a shell
     function, then suspending it will have the effect of causing
     the  shell to fork.  This is necessary to separate the func-
     tion's state from that of the parent  shell  performing  the
     job  control,  so  that the latter can return to the command
     line prompt.  As a result, even if fg is  used  to  continue
     the  job  the  function will no longer be part of the parent
     shell, and any variables set by the  function  will  not  be
     visible  in the parent shell.  Thus the behaviour is differ-
     ent from the case where the function  was  never  suspended.
     Zsh is different from many other shells in this regard.

     The same behaviour is found when the shell is executing code
     as the right hand side of a pipeline or  any  complex  shell
     construct  such  as  if, for, etc., in order that the entire
     block of code can be managed as a  single  job.   Background
     jobs are normally allowed to produce output, but this can be
     disabled by giving the command `stty tostop'.   If  you  set
     this tty option, then background jobs will suspend when they
     try to produce output like they do when  they  try  to  read

     When  a command is suspended and continued later with the fg
     or wait builtins, zsh restores tty modes that were in effect
     when  it was suspended.  This (intentionally) does not apply
     if the command is continued via `kill -CONT', nor when it is
     continued with bg.

     There are several ways to refer to jobs in the shell.  A job
     can be referred to by the process ID of any process  of  the
     job or by one of the following:

          The job with the given number.
          Any job whose command line begins with string.

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          Any job whose command line contains string.
     %%   Current job.
     %+   Equivalent to `%%'.
     %-   Previous job.

     The  shell  learns  immediately  whenever  a process changes
     state.  It normally  informs  you  whenever  a  job  becomes
     blocked  so  that  no  further progress is possible.  If the
     NOTIFY option is not set, it  waits  until  just  before  it
     prints  a  prompt before it informs you.  All such notifica-
     tions are sent directly to the terminal, not to the standard
     output or standard error.

     When  the  monitor mode is on, each background job that com-
     pletes triggers any trap set for CHLD.

     When you try to leave the shell while jobs  are  running  or
     suspended, you will be warned that `You have suspended (run-
     ning) jobs'.  You may use the jobs command to see what  they
     are.   If  you do this or immediately try to exit again, the
     shell will not warn you a second time;  the  suspended  jobs
     will  be  terminated,  and  the  running jobs will be sent a
     SIGHUP signal, if the HUP option is set.

     To avoid having the shell terminate the running jobs, either
     use  the nohup command (see nohup(1)) or the disown builtin.

     The INT and QUIT signals for an invoked command are  ignored
     if  the command is followed by `&' and the MONITOR option is
     not active.  The shell itself always ignores the  QUIT  sig-
     nal.   Otherwise,  signals  have the values inherited by the
     shell from its parent (but see the TRAPNAL special functions
     in the section `Functions').

     Certain  jobs are run asynchronously by the shell other than
     those explicitly put into  the  background;  even  in  cases
     where  the  shell  would  usually  wait  for  such  jobs, an
     explicit exit command or exit due  to  the  option  ERR_EXIT
     will  cause  the shell to exit without waiting.  Examples of
     such asynchronous jobs are  process  substitution,  see  the
     section  PROCESS SUBSTITUTION in the zshexpn(1) manual page,
     and the handler processes for multios, see the section  MUL-
     TIOS in the zshmisc(1) manual page.

     The shell can perform integer and floating point arithmetic,
     either using the builtin let, or via a substitution  of  the
     form  $((...)).  For integers, the shell is usually compiled
     to use 8-byte precision where this is  available,  otherwise
     precision  is  4 bytes.  This can be tested, for example, by

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     giving the command `print - $(( 12345678901 ))'; if the num-
     ber  appears  unchanged,  the precision is at least 8 bytes.
     Floating point arithmetic always uses the `double' type with
     whatever corresponding precision is provided by the compiler
     and the library.

     The let builtin  command  takes  arithmetic  expressions  as
     arguments;  each is evaluated separately.  Since many of the
     arithmetic operators, as well as spaces, require quoting, an
     alternative  form  is provided: for any command which begins
     with a `((', all the characters until a  matching  `))'  are
     treated as a quoted expression and arithmetic expansion per-
     formed as for an argument of let.  More precisely, `((...))'
     is equivalent to `let "..."'.  The return status is 0 if the
     arithmetic value of the expression is non-zero, 1 if  it  is
     zero, and 2 if an error occurred.

     For example, the following statement

          (( val = 2 + 1 ))

     is equivalent to

          let "val = 2 + 1"

     both  assigning  the  value  3 to the shell variable val and
     returning a zero status.

     Integers can be in bases other than 10.  A leading  `0x'  or
     `0X'  denotes hexadecimal.  Integers may also be of the form
     `base#n', where base is a decimal  number  between  two  and
     thirty-six  representing the arithmetic base and n is a num-
     ber in that base (for example, `16#ff' is 255  in  hexadeci-
     mal).   The base# may also be omitted, in which case base 10
     is used.  For backwards compatibility the form `[base]n'  is
     also accepted.

     An  integer  expression or a base given in the form `base#n'
     may contain underscores (`_') after the  leading  digit  for
     visual guidance; these are ignored in computation.  Examples
     are 1_000_000 or 0xffff_ffff which are equivalent to 1000000
     and 0xffffffff respectively.

     It  is also possible to specify a base to be used for output
     in the form `[#base]', for example `[#16]'.   This  is  used
     when outputting arithmetical substitutions or when assigning
     to scalar parameters, but an explicitly defined  integer  or
     floating  point parameter will not be affected.  If an inte-
     ger variable is implicitly defined by an arithmetic  expres-
     sion,  any  base  specified  in  this way will be set as the
     variable's output arithmetic base as if the option `-i base'
     to the typeset builtin had been used.  The expression has no

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User Commands                                          ZSHMISC(1)

     precedence and if it occurs more than once in a mathematical
     expression, the last encountered is used.  For clarity it is
     recommended that it appear at the beginning  of  an  expres-
     sion.  As an example:

          typeset -i 16 y
          print $(( [#8] x = 32, y = 32 ))
          print $x $y

     outputs  first `8#40', the rightmost value in the given out-
     put base, and then `8#40 16#20', because y has been  explic-
     itly  declared  to have output base 16, while x (assuming it
     does not already exist) is implicitly typed  by  the  arith-
     metic evaluation, where it acquires the output base 8.

     If  the  C_BASES  option  is set, hexadecimal numbers in the
     standard C format, for example 0xFF  instead  of  the  usual
     `16#FF'.   If the option OCTAL_ZEROES is also set (it is not
     by default), octal numbers will  be  treated  similarly  and
     hence appear as `077' instead of `8#77'.  This option has no
     effect on the output of bases  other  than  hexadecimal  and
     octal, and these formats are always understood on input.

     When an output base is specified using the `[#base]' syntax,
     an appropriate base prefix will be output if  necessary,  so
     that  the  value output is valid syntax for input.  If the #
     is doubled, for example `[##16]', then  no  base  prefix  is

     Floating point constants are recognized by the presence of a
     decimal point or an exponent.  The decimal point may be  the
     first  character of the constant, but the exponent character
     e or E may not, as it will be taken for  a  parameter  name.
     All numeric parts (before and after the decimal point and in
     the exponent) may  contain  underscores  after  the  leading
     digit for visual guidance; these are ignored in computation.

     An arithmetic expression uses nearly  the  same  syntax  and
     associativity of expressions as in C.

     In the native mode of operation, the following operators are
     supported (listed in decreasing order of precedence):

     + - ! ~ ++ --
          unary    plus/minus,    logical    NOT,     complement,
     << >>
          bitwise shift left, right
     &    bitwise AND
     ^    bitwise XOR
     |    bitwise OR
     **   exponentiation

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User Commands                                          ZSHMISC(1)

     * / %
          multiplication, division, modulus (remainder)
     + -  addition, subtraction
     < > <= >=
     == !=
          equality and inequality
     &&   logical AND
     || ^^
          logical OR, XOR
     ? :  ternary operator
     = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
     ,    comma operator

     The  operators  `&&',  `||', `&&=', and `||=' are short-cir-
     cuiting, and only one of the latter  two  expressions  in  a
     ternary  operator  is evaluated.  Note the precedence of the
     bitwise AND, OR, and XOR operators.

     With the option C_PRECEDENCES the precedences (but no  other
     properties)  of  the operators are altered to be the same as
     those in most other  languages  that  support  the  relevant

     + - ! ~ ++ --
          unary     plus/minus,    logical    NOT,    complement,
     **   exponentiation
     * / %
          multiplication, division, modulus (remainder)
     + -  addition, subtraction
     << >>
          bitwise shift left, right
     < > <= >=
     == !=
          equality and inequality
     &    bitwise AND
     ^    bitwise XOR
     |    bitwise OR
     &&   logical AND
     ^^   logical XOR
     ||   logical OR
     ? :  ternary operator
     = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
     ,    comma operator

     Note the precedence of exponentiation in both cases is below
     that of unary operators, hence `-3**2' evaluates as `9', not
     -9.  Use parentheses where necessary:  `-(3**2)'.   This  is

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     for compatibility with other shells.

     Mathematical   functions  can  be  called  with  the  syntax
     `func(args)', where the function decides if the args is used
     as  a string or a comma-separated list of arithmetic expres-
     sions. The shell currently defines no mathematical functions
     by  default,  but the module zsh/mathfunc may be loaded with
     the zmodload builtin  to  provide  standard  floating  point
     mathematical functions.

     An  expression  of  the  form `##x' where x is any character
     sequence such as `a', `^A', or `\M-\C-x' gives the value  of
     this  character  and  an expression of the form `#foo' gives
     the value of the first character  of  the  contents  of  the
     parameter  foo.  Character values are according to the char-
     acter set used in the current locale; for multibyte  charac-
     ter  handling  the  option MULTIBYTE must be set.  Note that
     this form is different from `$#foo',  a  standard  parameter
     substitution  which  gives  the length of the parameter foo.
     `#\' is accepted instead of `##', but its use is deprecated.

     Named parameters and subscripted arrays can be referenced by
     name within  an  arithmetic  expression  without  using  the
     parameter expansion syntax.  For example,

          ((val2 = val1 * 2))

     assigns  twice  the  value  of  $val1 to the parameter named

     An internal integer representation of a named parameter  can
     be  specified  with the integer builtin.  Arithmetic evalua-
     tion is performed on the value of each assignment to a named
     parameter  declared  integer  in  this  manner.  Assigning a
     floating point number to an integer results in rounding down
     to the next integer.

     Likewise,  floating  point  numbers can be declared with the
     float builtin; there are two types, differing only in  their
     output  format,  as  described for the typeset builtin.  The
     output format can be bypassed by using arithmetic  substitu-
     tion  instead of the parameter substitution, i.e. `${float}'
     uses the defined format, but  `$((float))'  uses  a  generic
     floating point format.

     Promotion  of  integer to floating point values is performed
     where  necessary.   In  addition,  if  any  operator   which
     requires an integer (`~', `&', `|', `^', `%', `<<', `>>' and
     their equivalents with assignment) is given a floating point
     argument, it will be silently rounded down to the next inte-

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     Scalar variables can hold integer or floating  point  values
     at  different  times; there is no memory of the numeric type
     in this case.

     If a variable is first assigned in a numeric context without
     previously  being  declared,  it will be implicitly typed as
     integer or float and retain that type either until the  type
     is  explicitly  changed or until the end of the scope.  This
     can have unforeseen consequences.  For example, in the loop

          for (( f = 0; f < 1; f += 0.1 )); do
          # use $f

     if f has not already been  declared,  the  first  assignment
     will  cause it to be created as an integer, and consequently
     the operation `f += 0.1' will always cause the result to  be
     truncated to zero, so that the loop will fail.  A simple fix
     would be to turn the initialization into `f = 0.0'.   It  is
     therefore  best  to  declare numeric variables with explicit

     A conditional expression is used with the [[  compound  com-
     mand  to  test  attributes  of files and to compare strings.
     Each expression can be constructed from one or more  of  the
     following unary or binary expressions:

     -a file
          true if file exists.

     -b file
          true if file exists and is a block special file.

     -c file
          true if file exists and is a character special file.

     -d file
          true if file exists and is a directory.

     -e file
          true if file exists.

     -f file
          true if file exists and is a regular file.

     -g file
          true if file exists and has its setgid bit set.

     -h file
          true if file exists and is a symbolic link.

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     -k file
          true if file exists and has its sticky bit set.

     -n string
          true if length of string is non-zero.

     -o option
          true  if  option  named  option is on.  option may be a
          single character, in which case it is a  single  letter
          option name.  (See the section `Specifying Options'.)

     -p file
          true  if  file exists and is a FIFO special file (named

     -r file
          true if file exists and is readable by current process.

     -s file
          true if file exists and has size greater than zero.

     -t fd
          true  if  file descriptor number fd is open and associ-
          ated  with  a  terminal  device.   (note:  fd  is   not

     -u file
          true if file exists and has its setuid bit set.

     -w file
          true if file exists and is writable by current process.

     -x file
          true if  file  exists  and  is  executable  by  current
          process.   If  file exists and is a directory, then the
          current process has permission to search in the  direc-

     -z string
          true if length of string is zero.

     -L file
          true if file exists and is a symbolic link.

     -O file
          true  if file exists and is owned by the effective user
          ID of this process.

     -G file
          true if file exists and its group matches the effective
          group ID of this process.

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User Commands                                          ZSHMISC(1)

     -S file
          true if file exists and is a socket.

     -N file
          true  if  file  exists and its access time is not newer
          than its modification time.

     file1 -nt file2
          true if file1 exists and is newer than file2.

     file1 -ot file2
          true if file1 exists and is older than file2.

     file1 -ef file2
          true if file1 and file2 exist and  refer  to  the  same

     string = pattern
     string == pattern
          true  if  string matches pattern.  The `==' form is the
          preferred one.  The `=' form is for  backward  compati-
          bility and should be considered obsolete.

     string != pattern
          true if string does not match pattern.

     string =~ regexp
          true  if  string matches the regular expression regexp.
          If the option RE_MATCH_PCRE is set regexp is tested  as
          a  PCRE  regular  expression using the zsh/pcre module,
          else it is tested as a POSIX extended  regular  expres-
          sion  using  the  zsh/regex  module.   Upon  successful
          match, some variables will be updated; no variables are
          changed if the matching fails.

          If the option BASH_REMATCH is not set the scalar param-
          eter MATCH is set to the  substring  that  matched  the
          pattern  and  the integer parameters MBEGIN and MEND to
          the index of the start and end,  respectively,  of  the
          match  in  string,  such that if string is contained in
          variable var the expression `${var[$MBEGIN,$MEND]}'  is
          identical  to  `$MATCH'.   The  setting  of  the option
          KSH_ARRAYS is respected.  Likewise, the array match  is
          set to the substrings that matched parenthesised subex-
          pressions and the arrays mbegin and mend to the indices
          of  the  start  and end positions, respectively, of the
          substrings within string.  The arrays are  not  set  if
          there were no parenthesised subexpresssions.  For exam-
          ple, if the string `a short string' is matched  against
          the  regular  expression  `s(...)t', then (assuming the
          option KSH_ARRAYS is not set) MATCH,  MBEGIN  and  MEND
          are `short', 3 and 7, respectively, while match, mbegin

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          and mend are single entry arrays containing the strings
          `hor', `4' and `6, respectively.

          If   the   option   BASH_REMATCH   is   set  the  array
          BASH_REMATCH is set to the substring that  matched  the
          pattern  followed by the substrings that matched paren-
          thesised subexpressions within the pattern.

     string1 < string2
          true if string1 comes before  string2  based  on  ASCII
          value of their characters.

     string1 > string2
          true  if  string1  comes  after  string2 based on ASCII
          value of their characters.

     exp1 -eq exp2
          true if exp1 is numerically equal to exp2.   Note  that
          for  purely  numeric  comparisons  use  of  the ((...))
          builtin described in the  section  `ARITHMETIC  EVALUA-
          TION'  is more convenient than conditional expressions.

     exp1 -ne exp2
          true if exp1 is numerically not equal to exp2.

     exp1 -lt exp2
          true if exp1 is numerically less than exp2.

     exp1 -gt exp2
          true if exp1 is numerically greater than exp2.

     exp1 -le exp2
          true if exp1 is numerically less than or equal to exp2.

     exp1 -ge exp2
          true  if  exp1  is numerically greater than or equal to

     ( exp )
          true if exp is true.

     ! exp
          true if exp is false.

     exp1 && exp2
          true if exp1 and exp2 are both true.

     exp1 || exp2
          true if either exp1 or exp2 is true.

     Normal shell expansion is performed on the file, string  and
     pattern  arguments,  but  the  result  of  each expansion is

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User Commands                                          ZSHMISC(1)

     constrained to be a single word, similar to  the  effect  of
     double  quotes.  Filename generation is not performed on any
     form of argument to conditions.  However, pattern  metachar-
     acters  are  active  for the pattern arguments; the patterns
     are the same as those used for filename generation, see zsh-
     expn(1),  but  there is no special behaviour of `/' nor ini-
     tial dots, and no glob qualifiers are allowed.

     In each of the above expressions, if file  is  of  the  form
     `/dev/fd/n', where n is an integer, then the test applied to
     the open file whose descriptor number  is  n,  even  if  the
     underlying system does not support the /dev/fd directory.

     In  the  forms  which do numeric comparison, the expressions
     exp undergo arithmetic expansion as if they were enclosed in

     For example, the following:

          [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.

     tests  if  either file foo or file bar exists, and if so, if
     the value of the parameter report begins with  `y';  if  the
     complete  condition  is  true, the message `File exists.' is

     Prompt sequences undergo a special form of expansion.   This
     type  of  expansion is also available using the -P option to
     the print builtin.

     If the PROMPT_SUBST option is  set,  the  prompt  string  is
     first subjected to parameter expansion, command substitution
     and arithmetic expansion.  See zshexpn(1).

     Certain escape sequences may be  recognised  in  the  prompt

     If  the  PROMPT_BANG  option  is set, a `!' in the prompt is
     replaced by the current history event number.  A literal `!'
     may then be represented as `!!'.

     If   the   PROMPT_PERCENT  option  is  set,  certain  escape
     sequences that start with `%' are  expanded.   Many  escapes
     are  followed  by a single character, although some of these
     take an optional integer argument that should appear between
     the  `%'  and the next character of the sequence.  More com-
     plicated escape sequences are available  to  provide  condi-
     tional expansion.


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User Commands                                          ZSHMISC(1)

  Special characters
     %%   A `%'.

     %)   A `)'.

  Login information
     %l   The  line  (tty)  the  user  is  logged  in on, without
          `/dev/' prefix.  If the name  starts  with  `/dev/tty',
          that prefix is stripped.

     %M   The full machine hostname.

     %m   The  hostname up to the first `.'.  An integer may fol-
          low the `%' to specify how many components of the host-
          name  are  desired.   With a negative integer, trailing
          components of the hostname are shown.

     %n   $USERNAME.

     %y   The line (tty)  the  user  is  logged  in  on,  without
          `/dev/'  prefix.   This does not treat `/dev/tty' names

  Shell state
     %#   A `#' if the shell is running with privileges, a `%' if
          not.   Equivalent  to  `%(!.#.%%)'.   The definition of
          `privileged', for these purposes, is  that  either  the
          effective user ID is zero, or, if POSIX.1e capabilities
          are supported, that at least one capability  is  raised
          in  either the Effective or Inheritable capability vec-

     %?   The return status of the  last  command  executed  just
          before the prompt.

     %_   The  status  of  the  parser, i.e. the shell constructs
          (like `if' and `for') that have  been  started  on  the
          command  line.  If  given  an  integer number that many
          strings will be printed; zero or negative or no integer
          means  print as many as there are.  This is most useful
          in prompts PS2  for  continuation  lines  and  PS4  for
          debugging with the XTRACE option; in the latter case it
          will also work non-interactively.

     /    Current working directory.  If an integer  follows  the
          `%',  it  specifies  a number of trailing components of
          the current working directory to show; zero  means  the
          whole  path.  A negative integer specifies leading com-
          ponents, i.e. %-1d specifies the first component.

     %~   As %d and %/, but  if  the  current  working  directory

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User Commands                                          ZSHMISC(1)

          starts with $HOME, that part is replaced by a `~'. Fur-
          thermore, if it has a named directory  as  its  prefix,
          that  part is replaced by a `~' followed by the name of
          the directory, but only if the result is  shorter  than
          the full path; see Dynamic and Static named directories
          in zshexpn(1).

     %!   Current history event number.

     %i   The line number currently being executed in the script,
          sourced  file,  or shell function given by %N.  This is
          most useful for debugging as part of $PS4.

     %I   The line number currently being executed  in  the  file
          %x.   This  is  similar  to  %i, but the line number is
          always a line number in the file  where  the  code  was
          defined, even if the code is a shell function.

     %j   The number of jobs.

     %L   The current value of $SHLVL.

     %N   The name of the script, sourced file, or shell function
          that zsh is currently executing, whichever was  started
          most recently.  If there is none, this is equivalent to
          the parameter $0.  An integer may  follow  the  `%'  to
          specify  a  number of trailing path components to show;
          zero means the full path.  A negative integer specifies
          leading components.

     %x   The  name  of  the file containing the source code cur-
          rently being executed.  This behaves as %N except  that
          function  and eval command names are not shown, instead
          the file where they were defined.

     %C   Trailing component of the  current  working  directory.
          An integer may follow the `%' to get more than one com-
          ponent.  Unless `%C' is used, tilde contraction is per-
          formed  first.   These  are deprecated as %c and %C are
          equivalent to %1~ and %1/, respectively, while explicit
          positive  integers have the same effect as for the lat-
          ter two sequences.

  Date and time
     %D   The date in yy-mm-dd format.

     %T   Current time of day, in 24-hour format.


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User Commands                                          ZSHMISC(1)

     %@   Current time of day, in 12-hour, am/pm format.

     %*   Current time of day in 24-hour format, with seconds.

     %w   The date in day-dd format.

     %W   The date in mm/dd/yy format.

          string is formatted using the strftime  function.   See
          strftime(3)  for  more details.  Various zsh extensions
          provide numbers with no leading zero or  space  if  the
          number is a single digit:

          %f   a day of the month
          %K   the hour of the day on the 24-hour clock
          %L   the hour of the day on the 12-hour clock

          The GNU extension that a `-' between the % and the for-
          mat character causes a leading  zero  or  space  to  be
          stripped  is handled directly by the shell for the for-
          mat characters d, f, H, k, l, m, M, S and y; any  other
          format  characters  are provided to strftime() with any
          leading `-', present, so the handling is system  depen-
          dent.   Further  GNU  extensions  are  not supported at

  Visual effects
     %B (%b)
          Start (stop) boldface mode.

     %E   Clear to end of line.

     %U (%u)
          Start (stop) underline mode.

     %S (%s)
          Start (stop) standout mode.

     %F (%f)
          Start (stop) using a different  foreground  colour,  if
          supported by the terminal.  The colour may be specified
          two ways: either as a numeric argument, as  normal,  or
          by  a  sequence in braces following the %F, for example
          %F{red}.  In the latter case the values allowed are  as
          described for the fg zle_highlight attribute; see Char-
          acter  Highlighting  in  zshzle(1).   This  means  that
          numeric  colours are allowed in the second format also.

     %K (%k)
          Start (stop) using a different bacKground colour.   The
          syntax is identical to that for %F and %f.

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User Commands                                          ZSHMISC(1)

          Include  a  string  as  a literal escape sequence.  The
          string within the braces should not change  the  cursor
          position.  Brace pairs can nest.

          A  positive numeric argument between the % and the { is
          treated as described for %G below.

     %G   Within a %{...%} sequence, include a `glitch': that is,
          assume  that  a  single character width will be output.
          This is useful when outputting characters  that  other-
          wise  cannot be correctly handled by the shell, such as
          the alternate character set  on  some  terminals.   The
          characters in question can be included within a %{...%}
          sequence together with the  appropriate  number  of  %G
          sequences  to  indicate  the correct width.  An integer
          between the `%' and `G'  indicates  a  character  width
          other  than  one.   Hence  %{seq%2G%}  outputs  seq and
          assumes it takes up the width of two  standard  charac-

          Multiple  uses of %G accumulate in the obvious fashion;
          the position of the %G is unimportant.  Negative  inte-
          gers are not handled.

          Note that when prompt truncation is in use it is advis-
          able to divide up output into single characters  within
          each %{...%} group so that the correct truncation point
          can be found.

     %v   The value of the  first  element  of  the  psvar  array
          parameter.   Following  the  `%'  with an integer gives
          that element of the  array.   Negative  integers  count
          from the end of the array.

          Specifies  a ternary expression.  The character follow-
          ing the x is arbitrary; the same character is  used  to
          separate  the  text for the `true' result from that for
          the `false' result.  This separator may not  appear  in
          the  true-text,  except as part of a %-escape sequence.
          A `)' may appear in the false-text as `%)'.   true-text
          and  false-text  may  both  contain  arbitrarily-nested
          escape sequences,  including  further  ternary  expres-

          The  left  parenthesis may be preceded or followed by a
          positive integer n, which defaults to zero.  A negative
          integer will be multiplied by -1.  The test character x
          may be any of the following:

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User Commands                                          ZSHMISC(1)

          !    True if the shell is running with privileges.
          #    True if the effective uid of the  current  process
               is n.
          ?    True if the exit status of the last command was n.
          _    True if at least n shell constructs were  started.
          /    True  if  the current absolute path has at least n
               elements relative to the root directory,  hence  /
               is counted as 0 elements.
          ~    True if the current path, with prefix replacement,
               has at least  n  elements  relative  to  the  root
               directory, hence / is counted as 0 elements.
          D    True if the month is equal to n (January = 0).
          d    True if the day of the month is equal to n.
          g    True  if  the effective gid of the current process
               is n.
          j    True if the number of jobs is at least n.
          L    True if the SHLVL parameter is at least n.
          l    True if at least n characters  have  already  been
               printed on the current line.
          S    True if the SECONDS parameter is at least n.
          T    True if the time in hours is equal to n.
          t    True if the time in minutes is equal to n.
          v    True if the array psvar has at least n elements.
          V    True  if  element  n of the array psvar is set and
          w    True if the day of the week is equal to n  (Sunday
               = 0).

          Specifies truncation behaviour for the remainder of the
          prompt string.  The third, deprecated, form is  equiva-
          lent  to  `%xstringx',  i.e.  x may be `<' or `>'.  The
          numeric argument, which in the third  form  may  appear
          immediately  after  the `[', specifies the maximum per-
          mitted length of the various strings that can  be  dis-
          played  in the prompt.  The string will be displayed in
          place of the truncated portion of any string; note this
          does not undergo prompt expansion.

          The  forms with `<' truncate at the left of the string,
          and the forms with `>' truncate at  the  right  of  the
          string.   For  example,  if  the  current  directory is
          `/home/pike', the  prompt  `%8<..<%/'  will  expand  to
          `..e/pike'.   In this string, the terminating character
          (`<', `>' or `]'), or in fact  any  character,  may  be
          quoted  by  a  preceding `\'; note when using print -P,
          however, that this must be doubled  as  the  string  is

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User Commands                                          ZSHMISC(1)

          also  subject to standard print processing, in addition
          to any backslashes removed by a double  quoted  string:
          the worst case is therefore `print -P "%<\\\\<<..."'.

          If  the  string is longer than the specified truncation
          length, it will appear in  full,  completely  replacing
          the truncated string.

          The  part  of the prompt string to be truncated runs to
          the end of the string,  or  to  the  end  of  the  next
          enclosing  group  of the `%(' construct, or to the next
          truncation encountered at the same grouping level (i.e.
          truncations  inside  a  `%('  are separate), which ever
          comes first.  In particular, a truncation with argument
          zero  (e.g.  `%<<')  marks  the end of the range of the
          string to be truncated  while  turning  off  truncation
          from there on. For example, the prompt '%10<...<%~%<<%#
          ' will print a truncated representation of the  current
          directory,  followed  by  a  `%'  or `#', followed by a
          space.  Without the `%<<', those two  characters  would
          be included in the string to be truncated.

     See   attributes(5)   for   descriptions  of  the  following

     |Availability   | shell/zsh        |
     |Stability      | Volatile         |
     This  software  was   built   from   source   available   at    The  original
     community   source   was   downloaded   from    http://down-

     Further information about this software can be found on  the
     open source community website at

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