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Updated: Thursday, June 13, 2019

zshmisc (1)


zshmisc - everything and then some


Please see following description for synopsis


ZSHMISC(1)                  General Commands Manual                 ZSHMISC(1)

       zshmisc - everything and then some

       A  simple  command is a sequence of optional parameter assignments fol-
       lowed by  blank-separated  words,  with  optional  redirections  inter-
       spersed.   For  a  description of assignment, see the beginning of zsh-

       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 command, unless the  pipe-
       line  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 operators 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 ordi-
       nary background job.

       A  sublist  is  either  a single pipeline, or a sequence of two or more
       pipelines separated by `&&' or `||'.  If two pipelines 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 operators have equal precedence and  are  left  associative.   The
       value  of  the sublist is the value of the last pipeline executed.  For

              dmesg | grep panic && print yes

       is a sublist consisting of two pipelines, the second just a simple com-
       mand  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

       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 sublist 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  executing  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 what-
       soever, including the complex commands below; this is implied  wherever
       the  word  `list' appears in later descriptions.  For example, the com-
       mands 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  modifiers are shell
       builtin commands with the exception of nocorrect which  is  a  reserved

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

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

       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 spe-
              cial 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.

       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 compatibility with other shells.

              The -c option clears the environment.

              The  -l  option  is  equivalent to the - precommand modifier, 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  inter-
              preted  immediately,  before  any  parsing  is  done.  It has no
              effect in non-interactive shells.

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

       A complex command in zsh is one of the following:

       if list then list [ elif list then list ] ... [ else list ] fi
              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, exe-
              cuting list each time.  If the in word is omitted, use the posi-
              tional 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 of the loop
              the  next  N words are assigned to the corresponding 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

       for (( [expr1] ; [expr2] ; [expr3] )) do list done
              The arithmetic expression expr1 is evaluated first (see the sec-
              tion `Arithmetic Evaluation').  The arithmetic expression  expr2
              is  repeatedly  evaluated  until  it  evaluates 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 evaluated 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

       repeat word do list done
              word is expanded and treated as an arithmetic expression,  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'

       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'.

              Note further that, unless the SH_GLOB option is set,  the  whole
              pattern  with alternatives is treated by the shell as equivalent
              to a group of patterns within parentheses, although white  space
              may  appear  about the parentheses and the vertical bar and will
              be stripped from the pattern at those points.  White  space  may
              appear  elsewhere  in the pattern; this is not stripped.  If the
              SH_GLOB option is set, so that an  opening  parenthesis  can  be
              unambiguously treated as part of the case syntax, the expression
              is parsed into separate words and these are  treated  as  strict
              alternatives (as in other shells).

              If  the  list that is executed is terminated with ;& rather than
              ;;, the following list is also executed.  The rule for the  ter-
              minator 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, exe-
              cuting the corresponding list, and applying  the  rule  for  the
              corresponding  terminator  ;;,  ;& or ;|.  Note that word is not
              re-expanded; all applicable patterns are tested  with  the  same

       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 number.   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 interactive 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 corresponding 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 selec-
              tion 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 executing list.

       { list }
              Execute list.

       { try-list } always { always-list }
              First  execute  try-list.   Regardless of errors, or break, con-
              tinue, or return commands encountered within  try-list,  execute
              always-list.   Execution  then  continues from the result of the
              execution of try-list; in other words, any error, or break, con-
              tinue,  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  func-
              tion,  script,  or  list.   Syntax  errors encountered while the
              shell is parsing the code do not cause  the  always-list  to  be
              executed.   For  example, 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 substitu-
              tion such as ${*foo*} would cause a run-time error, after  which
              always-list would be executed.

              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  initialised  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 use-
              ful (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  try-list.
              This   will   be  non-zero  if  there  was  an  error,  even  if
              TRY_BLOCK_ERROR was set to zero.

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

                         # 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 function 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 function is the list between the  {  and
              }.  See the section `Functions'.

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

              In  any of the forms above, a redirection may appear outside the
              function body, for example

                     func() { ... } 2>&1

              The redirection is stored with the function and applied whenever
              the  function is executed.  Any variables in the redirection are
              expanded at the point the function is executed, but outside  the
              function scope.

       time [ pipeline ]
              The  pipeline is executed, and timing statistics are reported on
              the standard error in the form specified by the TIMEFMT  parame-
              ter.   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 `Conditional 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  com-
       mands, in both these cases the test part of the loop must also be suit-
       ably 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 limitations  on  the
              form of list apply as for the previous form.

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

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

       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

       function word ... [ () ] [ term ] sublist
              This is a short form of function.

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

       do done esac then elif else fi for case if while function  repeat  time
       until select coproc nocorrect foreach end ! [[ { } declare export float
       integer local readonly typeset

       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  command  line,  and  in  a
       non-interactive  shell  they  cause  the shell to be aborted.  In older
       versions of zsh, a non-interactive 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 illogical behav-
       iour can be recovered by setting the option CONTINUE_ON_ERROR.

       Fatal errors found in non-interactive shells include:

       o      Failure to parse shell options passed when invoking the shell

       o      Failure to change options with the set builtin

       o      Parse errors of all sorts, including failures to parse mathemat-
              ical expressions

       o      Failures  to  set  or  modify  variable  behaviour with typeset,
              local, declare, export, integer, float

       o      Execution of  incorrectly  positioned  loop  control  structures
              (continue, break)

       o      Attempts  to  use  regular expression with no regular expression
              module available

       o      Disallowed operations when the RESTRICTED options is set

       o      Failure to create a pipe needed for a pipeline

       o      Failure to create a multio

       o      Failure to autoload a module needed for a declared shell feature

       o      Errors creating command or process substitutions

       o      Syntax errors in glob qualifiers

       o      File generation errors where not caught by the  option  BAD_PAT-

       o      All bad patterns used for matching within case statements

       o      File generation failures where not caused by NO_MATCH or similar

       o      All file generation errors where the pattern was used to  create
              a multio

       o      Memory errors where detected by the shell

       o      Invalid subscripts to shell variables

       o      Attempts to assign read-only variables

       o      Logical  errors  with  variables such as assignment to the wrong

       o      Use of invalid variable names

       o      Errors in variable substitution syntax

       o      Failure to convert characters in $'...' expressions

       If the POSIX_BUILTINS option is set, more errors associated with  shell
       builtin  commands are treated as fatal, as specified by the POSIX stan-

       In non-interactive shells, or in interactive shells with  the  INTERAC-
       TIVE_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.

       Every eligible word 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 replacement text ends with
       a  space,  the next word in the shell input is always eligible for pur-
       poses of alias expansion.  An alias is defined using the alias builtin;
       global aliases may be defined using the -g option to that builtin.

       A word is defined as:

       o      Any plain string or glob pattern

       o      Any  quoted  string,  using  any  quoting  method (note that the
              quotes must be part of the alias definition for this to be  eli-

       o      Any parameter reference or command substitution

       o      Any  series of the foregoing, concatenated without whitespace or
              other tokens between them

       o      Any reserved word (case, do, else, etc.)

       o      With global aliasing, any  command  separator,  any  redirection
              operator, and `(' or `)' when not part of a glob pattern

       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

       When POSIX_ALIASES is set, only plain unquoted strings are eligible for
       aliasing.   The  alias  builtin does not reject ineligible aliases, but
       they are not expanded.

       For use with completion, which would remove an initial  backslash  fol-
       lowed  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.

   Alias difficulties
       Although aliases can be used in ways that bend normal shell syntax, not
       every string of non-white-space characters can be used as an alias.

       Any set of characters not listed as a word above is not a  word,  hence
       no  attempt  is  made  to  expand  it  as an alias, no matter how it is
       defined  (i.e.  via  the  builtin  or  the  special  parameter  aliases
       described  in  the  section THE ZSH/PARAMETER MODULE in zshmodules(1)).
       However, as noted in the case of POSIX_ALIASES above,  the  shell  does
       not  attempt  to deduce whether the string corresponds to a word at the
       time the alias is created.

       For example, an expression containing an = at the start  of  a  command
       line  is  an assignment and cannot be expanded as an alias; a lone = is
       not an assignment but can only be set as an alias using the  parameter,
       as otherwise the = is taken part of the syntax of the builtin command.

       It  is  not  presently possible to alias the `((' token that introduces
       arithmetic expressions, because until a full statement has been parsed,
       it  cannot be distinguished from two consecutive `(' tokens introducing
       nested subshells.  Also, if a separator such  as  &&  is  aliased,  \&&
       turns into the two tokens \& and &, each of which may have been aliased
       separately.  Similarly for \<<, \>|, etc.

       There is a commonly encountered problem with aliases illustrated 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 `.'.  Con-
       sequently, use of functions  rather  than  aliases  is  recommended  in
       non-interactive code.

       Note  also  the  unhelpful  interaction of aliases and function defini-

              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 $*

       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  func-
       tion  definition  form  `function func'.  Ensuring the alias is defined
       after the function works but is problematic if the code fragment  might
       be re-executed.

       A  character  may be quoted (that is, made to stand for itself) by pre-
       ceding it with a `\'.  `\' followed by a newline 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 con-
       sidered 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 substitution occur,
       and `\' quotes the characters `\', ``', `"', `$', and the first charac-
       ter of $histchars (default `!').

       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 execution of a command contains the
       file descriptors of the invoking  shell  as  modified  by  input/output

       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 pro-
       duces more than one filename,  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.

       > 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 CLOB-
              BER 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 substitu-
              tion or filename generation is performed on word.  The resulting
              document, called a here-document, becomes the standard input.

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

              Note  that  word itself does not undergo shell expansion.  Back-
              quotes 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.  Compare the use of word
              in here-documents above,  where  word  does  not  undergo  shell

       <& 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

       >& word
       &> word
              (Except  where `>& word' matches one of the above syntaxes; `&>'
              can always be used to avoid  this  ambiguity.)   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 sec-
              tion below).

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

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

       >>&| word
       >>&! word
       &>>| word
       &>>! word
              Redirects both standard output and standard error (file descrip-
              tor 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 redirections are specified is significant.  The
       shell evaluates each redirection in  terms  of  the  (file  descriptor,
       file) association at the time of evaluation.  For example:

              ... 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 redirections were reversed, file descrip-
       tor 2 would be associated 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  redirect-
       ion.   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 operator there is a valid shell identi-
       fier 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
       identifier to the file descriptor opened.   No  whitespace  is  allowed
       between the closing brace and the redirection character.  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  read-

       If  the option CLOBBER is unset, it is an error to open a file descrip-
       tor 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 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 con-
       venient 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 processed.

       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 outputs, 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.

       Note also that redirections are always expanded in order.  This happens
       regardless of the setting of the MULTIOS option, but with the option in
       effect there are additional consequences. For example, the  meaning  of
       the expression >&1 will change after a previous redirection:

              date >&1 >output

       In  the  case above, the >&1 refers to the standard output at the start
       of the line; the result is similar to the tee command.   However,  con-

              date >output >&1

       As redirections are evaluated in order, when the >&1 is encountered the
       standard output is set to the file output and another copy of the  out-
       put  is  therefore  sent  to that file.  This is unlikely to be what is

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

              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 redirect-
       ion  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 inputs).

       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 Hello > bar > baz

       when MULTIOS is unset will  truncate  `bar',  and  write  `Hello'  into

       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  contents 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 parent 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 current shell:

              { cat file } >file >file2

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

       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_NULLCMD 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 com-
       mand 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 latter will be used instead of that of
       the former when the redirection 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  `Functions'.   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  unsuc-
       cessful,  the  shell prints an error message and returns a nonzero exit

       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 oper-
       ating systems that do not handle this executable format in the kernel.

       If  no  external command is found but a function command_not_found_han-
       dler exists the shell executes this  function  with  all  command  line
       arguments.  The return status of the function becomes the status of the
       command.  If the function wishes to mimic the behaviour  of  the  shell
       when the command is not found, it should print the message `command not
       found: cmd' to standard error and return status  127.   Note  that  the
       handler  is  executed  in a subshell forked to execute an external com-
       mand, 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 spe-
       cial syntax `funcname ()'.  Shell functions  are  read  in  and  stored
       internally.  Alias names are resolved when the function is read.  Func-
       tions are executed like commands with the  arguments  passed  as  posi-
       tional 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 envi-
       ronment of the caller.

       The return builtin is used to return from function calls.

       Function identifiers can be listed with the functions  builtin.   Func-
       tions can be undefined with the unfunction builtin.

       A  function  can  be marked as undefined using the autoload builtin (or
       `functions -u' or `typeset -fu').  Such a function 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 rec-
       ommended  for  the use of functions supplied 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.

       For each element in fpath, the shell looks for  three  possible  files,
       the newest of which is used to load the definition for the function:

              A  file  created  with  the  zcompile  builtin command, which is
              expected to contain the definitions for  all  functions  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 functions included
              must be explicitly recompiled by hand before the  shell  notices
              any changes.

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

              A file of zsh command text, taken to be the definition for func-

       In summary, the order of searching is, first, in the parents of  direc-
       tories  in  fpath  for  the  newer  of either a compiled directory or a
       directory in fpath; second, if more than one of these contains a  defi-
       nition  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 executed in the context of the function execu-
       tion, and may therefore define local parameters.  It is an error if the
       function is not defined by loading the file.

       Otherwise, the function body (with no surrounding  `funcname()  {...}')
       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  initializa-
       tion  and  then call the function defined, the file should contain ini-
       tialization 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 ini-
       tialization 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 searching  fpath,  by
       using  `autoload -X' within a shell function.  For example, the follow-
       ing 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 iden-
       tified by the presence of  the  comment  `#  undefined'  in  the  body,
       because all comments are discarded from defined functions.

       To load the definition of an autoloaded function myfunc without execut-
       ing 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 executed 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 following the clos-
       ing brace defining the function, hence if there are none  no  arguments
       (other than $0) are set.  This is a difference from the way other func-
       tions are parsed: normal function definitions may be followed  by  cer-
       tain  keywords  such  as `else' or `fi', which will be treated as argu-
       ments 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  function  called  at  this

       Redirections  may be applied to the anonymous function in the same man-
       ner 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  anony-
       mous  functions.   Instead, they are treated as normal function defini-
       tions where the definition is silently discarded.

       Certain functions, if defined, have special meaning to the shell.

   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 exe-
       cuted  in  the  same  context  and with the same arguments as the basic
       function.  For example, if $chpwd_functions is an array containing  the
       values  `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
       function'.  An error in any function causes subsequent functions not to
       be run.  Note further that an error in a precmd hook causes an  immedi-
       ately  following periodic function not to run (though it may run at the
       next opportunity).

       chpwd  Executed whenever the current working directory is changed.

              If the parameter PERIOD is set, this function is executed  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.

       precmd Executed before each prompt.  Note that precommand functions are
              not re-executed simply because the command 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 (regardless of
              whether the line was discarded from  the  history  buffer),  the
              string that the user typed is passed as the first argument, oth-
              erwise 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  ver-
              sion  of  the command (with things like function bodies elided);
              the third argument contains the full text  that  is  being  exe-

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

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

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

              A  hook function may call `fc -p ...' to switch the history con-
              text so that the history is saved in a different file  from  the
              that  in  the  global  HISTFILE parameter.  This is handled spe-
              cially: the history context is automatically restored after  the
              processing of the history 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  new-
              line  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 nor-
              mally.  This is not called by exiting subshells,  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.

              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 specially.  If it
              is zero, the signal is assumed to have been handled, and  execu-
              tion  continues  normally.   Otherwise, the shell will behave as
              interrupted except  that  the  return  status  of  the  trap  is

              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  exe-
              cuted inside other traps.

              If  the  option  DEBUG_BEFORE_CMD  is set (as it is by default),
              executed before each command; otherwise executed after each com-
              mand.  See the description of the trap builtin in zshbuiltins(1)
              for details of additional 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.  How-
              ever, 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  func-
              tion TRAPERR acts the same as TRAPZERR on systems where there is
              no SIGERR (this is the usual case).

       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

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

       o      The return status from function  traps  is  special,  whereas  a
              return from a list trap causes the surrounding 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  associates  a  job
       with  each  pipeline.  It keeps a table of current 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 control features described here.

       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  `sus-
       pended',  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  immedi-
       ately  and is like an interrupt in that pending output and unread input
       are discarded when it is typed.

       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 function'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 con-
       tinue 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 different from the case where  the  func-
       tion  was  never suspended.  Zsh is different from many other shells in
       this regard.

       One additional side effect is that use of disown with a job created  by
       suspending  shell  code in this fashion is delayed: the job can only be
       disowned once any process started from the parent shell has terminated.
       At that point, the disowned job disappears silently from the job list.

       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 input.

       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  sus-
       pended.   This (intentionally) does not apply if the command is contin-
       ued 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.
              The last job whose command line begins with string.
              The last job whose command line contains string.
       %%     Current job.
       %+     Equivalent to `%%'.
       %-     Previous job.

       The shell learns immediately whenever a process changes state.  It nor-
       mally  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 notifi-
       cations are sent directly to the terminal, not to the  standard  output
       or standard error.

       When  the  monitor mode is on, each background job that completes trig-
       gers 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 (running) jobs'.  You may
       use the jobs command to see what they are.  If you do this  or  immedi-
       ately 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 com-
       mand  is  followed  by  `&'  and the MONITOR option is not active.  The
       shell itself always ignores the QUIT signal.  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 MULTIOS in the zshmisc(1) manual

       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 giving the command `print - $(( 12345678901 ))'; if the
       number appears unchanged, the precision is at least 8 bytes.   Floating
       point  arithmetic  always  uses  the `double' type with whatever corre-
       sponding 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 match-
       ing `))' are treated as a quoted expression  and  arithmetic  expansion
       performed  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

       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 and a leading `0b' or `0B' binary.  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 number  in  that
       base  (for example, `16#ff' is 255 in hexadecimal).  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 arith-
       metical substitutions or when assigning to scalar  parameters,  but  an
       explicitly  defined  integer  or  floating  point parameter will not be
       affected.  If an integer variable is implicitly defined  by  an  arith-
       metic  expression,  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 precedence and if
       it occurs more than once in a mathematical expression, the last encoun-
       tered  is  used.   For  clarity it is recommended that it appear at the
       beginning of an expression.  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 output base, and
       then  `8#40 16#20', because y has been explicitly declared to have out-
       put base 16, while x (assuming it does not already exist) is implicitly
       typed  by  the arithmetic evaluation, where it acquires the output base

       The base may be replaced or followed by an underscore, which may itself
       be  followed  by  a  positive  integer (if it is missing the value 3 is
       used).  This indicates that underscores should  be  inserted  into  the
       output  string,  grouping the number for visual clarity.  The following
       integer specifies the number of digits to group together.  For example:

              setopt cbases
              print $(( [#16_4] 65536 ** 2 ))

       outputs `0x1_0000_0000'.

       The feature can be used with floating point numbers, in which case  the
       base  must  be  omitted;  grouping is away from the decimal point.  For

              zmodload zsh/mathfunc
              print $(( [#_] sqrt(1e7) ))

       outputs `3_162.277_660_168_379_5' (the number of decimal  places  shown
       may vary).

       If  the  C_BASES  option  is set, hexadecimal numbers are output 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 num-
       bers 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

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

       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, {pre,post}{in,de}cre-
       << >>  bitwise shift left, right
       &      bitwise AND
       ^      bitwise XOR
       |      bitwise OR
       **     exponentiation
       * / %  multiplication, division, modulus (remainder)
       + -    addition, subtraction
       < > <= >=
       == !=  equality and inequality
       &&     logical AND
       || ^^  logical OR, XOR
       ? :    ternary operator
       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
       ,      comma operator

       The operators `&&', `||', `&&=', and `||='  are  short-circuiting,  and
       only  one of the latter two expressions in a ternary operator is evalu-
       ated.  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 lan-
       guages that support the relevant operators:

       + - ! ~ ++ --
              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre-
       **     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  paren-
       theses  where  necessary:  `-(3**2)'.   This  is 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  expressions.  The  shell  currently
       defines  no mathematical functions by default, but the module zsh/math-
       func may be loaded with the zmodload builtin to provide standard float-
       ing 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 `#name' gives the value of the first character
       of the contents of the parameter name.  Character values are  according
       to  the character set used in the current locale; for multibyte charac-
       ter handling the option MULTIBYTE must be set.  Note that this form  is
       different  from `$#name', a standard parameter substitution which gives
       the length of the parameter name.  `#\' 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 val2.

       An  internal  integer representation of a named parameter can be speci-
       fied with the integer builtin.  Arithmetic evaluation 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 towards zero.

       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 substitution 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 neces-
       sary.   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 towards zero
       except for `~' which rounds down.

       Users should beware that, in common with many  other  programming  lan-
       guages  but not software designed for calculation, the evaluation of an
       expression in zsh is taken a term at a time and promotion  of  integers
       to  floating point does not occur in terms only containing integers.  A
       typical result of this is that a division such as 6/8 is truncated,  in
       this being rounded towards 0.  The FORCE_FLOAT shell option can be used
       in scripts or functions where floating  point  evaluation  is  required

       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 command to test
       attributes of files and to compare strings.   Each  expression  can  be
       constructed  from  one or more of the following unary or binary expres-

       -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.

       -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 char-
              acter,  in  which  case it is a single letter option name.  (See
              the section `Specifying Options'.)

              When no option  named  option  exists,  and  the  POSIX_BUILTINS
              option hasn't been set, return 3 with a warning.  If that option
              is set, return 1 with no warning.

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

       -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 associated with  a
              terminal device.  (note: fd is not optional)

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

       -v varname
              true if shell variable varname is 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 directory.

       -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.

       -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 file.

       string = pattern
       string == pattern
              true if string matches  pattern.   The  two  forms  are  exactly
              equivalent.   The  `=' form is the traditional shell syntax (and
              hence the only one generally used with the test and [ builtins);
              the  `=='  form  provides compatibility with other sorts of com-
              puter language.

       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  expression using the zsh/regex module.
              Upon successful match, some variables will be updated; no  vari-
              ables are changed if the matching fails.

              If the option BASH_REMATCH is not set the scalar parameter 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 sub-
              strings that matched parenthesised subexpressions 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
              example, 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 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 sub-
              strings that matched  parenthesised  subexpressions  within  the

       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  EVALUATION' is more convenient than condi-
              tional 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 exp2.

       ( 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.

       For compatibility, if there is a single argument that is not  syntacti-
       cally  significant, typically a variable, the condition is treated as a
       test for whether the expression expands as a string of non-zero length.
       In  other words, [[ $var ]] is the same as [[ -n $var ]].  It is recom-
       mended that the second, explicit, form be used where possible.

       Normal shell expansion is performed on the  file,  string  and  pattern
       arguments, but the result of each expansion is constrained to be a sin-
       gle word, similar to the effect of double quotes.

       Filename generation is not performed on any form of argument to  condi-
       tions.  However, it can be forced in any case where normal shell expan-
       sion is valid and when the option EXTENDED_GLOB is in effect  by  using
       an  explicit  glob qualifier of the form (#q) at the end of the string.
       A normal glob qualifier expression may appear between the `q'  and  the
       closing  parenthesis;  if  none  appears  the  expression has no effect
       beyond causing filename generation.  The results of filename generation
       are joined together to form a single word, as with the results of other
       forms of expansion.

       This special use of filename generation is only available with  the  [[
       syntax.   If the condition occurs within the [ or test builtin commands
       then globbing occurs instead as part of normal command  line  expansion
       before the condition is evaluated.  In this case it may generate multi-
       ple words which are likely to confuse the syntax of the test command.

       For example,

              [[ -n file*(#qN) ]]

       produces status zero if and only if there is at least one file  in  the
       current directory beginning with the string `file'.  The globbing qual-
       ifier N ensures that the expression is empty if there  is  no  matching

       Pattern  metacharacters  are active for the pattern arguments; the pat-
       terns are the same as those used  for  filename  generation,  see  zsh-
       expn(1), but there is no special behaviour of `/' nor initial 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 printed.

       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 string.

       If  the  PROMPT_BANG  option is set, a `!' in the prompt is replaced by
       the current history event number.  A literal `!'  may  then  be  repre-
       sented 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  complicated escape sequences are available to provide
       conditional expansion.

   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 follow the `%'
              to specify how many components  of  the  hostname  are  desired.
              With a negative integer, trailing components of the hostname are

       %n     $USERNAME.

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

   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 vectors.

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

       %_     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.

       %^     The  status  of  the parser in reverse. This is the same as `%_'
              other than the order of strings.  It is often used in RPS2.

       %/     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  inte-
              ger  specifies leading components, i.e. %-1d specifies the first

       %~     As %d and %/, but if the current working directory  starts  with
              $HOME,  that part is replaced by a `~'. Furthermore, 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  direc-
              tories in zshexpn(1).

       %e     Evaluation depth of the current sourced file, shell function, or
              eval.  This is incremented or decremented every time  the  value
              of  %N  is  set  or  reverted to a previous value, respectively.
              This is most useful for debugging as part of $PS4.

       %!     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

       %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 inte-
              ger may follow the `%' to specify a number of trailing path com-
              ponents  to  show; zero means the full path.  A negative integer
              specifies leading components.

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

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

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

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

       %@     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  strf-
              time(3)  for  more details.  Various zsh extensions provide num-
              bers with no leading zero or space if the  number  is  a  single

              %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

              In  addition, if the system supports the POSIX gettimeofday sys-
              tem call, %. provides decimal fractions of a  second  since  the
              epoch  with leading zeroes.  By default three decimal places are
              provided, but a number of digits up to 9 may be given  following
              the %; hence %6.  outputs microseconds, and %9. outputs nanosec-
              onds.  (The latter requires  a  nanosecond-precision  clock_get-
              time; systems lacking this will return a value multiplied by the
              appropriate power of 10.)  A typical example of this is the for-
              mat `%D{%H:%M:%S.%.}'.

              The GNU extension %N is handled as a synonym for %9..

              Additionally, the GNU extension that a `-' between the % and the
              format character causes a leading zero or space to  be  stripped
              is handled directly by the shell for the format characters d, f,
              H, k, l, m, M, S and y; any other format characters are provided
              to the system's strftime(3) with any leading `-' present, so the
              handling is system dependent.  Further GNU (or other) extensions
              are  also  passed to strftime(3) and may work if the system sup-
              ports them.

   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 Character 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.

              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 otherwise  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 characters.

              Multiple uses of %G accumulate in the obvious fashion; the posi-
              tion of the %G is unimportant.  Negative integers are  not  han-

              Note  that  when  prompt truncation is in use it is advisable 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 following 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 expressions.

              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, except as noted below for `l'.  The test char-
              acter x may be any of the following:

              !      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
              ~      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.
              e      True if the evaluation depth is at least 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.   When  n is negative, true if at
                     least abs(n) characters remain before the opposite margin
                     (thus the left margin for RPROMPT).
              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  equivalent  to
              `%xstringx', i.e. x may be `<' or `>'.  The string will be  dis-
              played  in  place  of  the truncated portion of any string; note
              this does not undergo prompt expansion.

              The numeric argument, which in the third form may appear immedi-
              ately  after  the `[', specifies the maximum permitted length of
              the various strings that can be displayed in the prompt.  In the
              first two forms, this numeric argument may be negative, in which
              case the truncation length  is  determined  by  subtracting  the
              absolute  value of the numeric argument from the number of char-
              acter positions remaining on the current prompt line.   If  this
              results in a zero or negative length, a length of 1 is used.  In
              other words, a negative argument arranges that after  truncation
              at  least n characters remain before the right margin (left mar-
              gin for RPROMPT).

              The forms with `<' truncate at the left of the string,  and  the
              forms  with  `>' truncate at the right of the string.  For exam-
              ple, if  the  current  directory  is  `/home/pike',  the  prompt
              `%8<..<%/'  will expand to `..e/pike'.  In this string, the ter-
              minating character (`<', `>' or `]'), or in fact any  character,
              may be quoted by a preceding `\'; note when using print -P, how-
              ever, that this must be doubled as the string is 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 sepa-
              rate), 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.
              Note  that `%-0<<' is not equivalent to `%<<' but specifies that
              the prompt is truncated at the right margin.

              Truncation applies only  within  each  individual  line  of  the
              prompt,  as  delimited  by  embedded  newlines (if any).  If the
              total length of any line  of  the  prompt  after  truncation  is
              greater  than the terminal width, or if the part to be truncated
              contains embedded newlines, truncation behavior is undefined and
              may   change   in   a   future   version   of  the  shell.   Use
              `%-n(l.true-text.false-text)' to remove parts of the prompt when
              the available space is less than n.

zsh 5.6.2                     September 14, 2018                    ZSHMISC(1)