GNU.WIKI: The GNU/Linux Knowledge Base

  [HOME] [PHP Manual] [HowTo] [ABS] [MAN1] [MAN2] [MAN3] [MAN4] [MAN5] [MAN6] [MAN7] [MAN8] [MAN9]

  [0-9] [Aa] [Bb] [Cc] [Dd] [Ee] [Ff] [Gg] [Hh] [Ii] [Jj] [Kk] [Ll] [Mm] [Nn] [Oo] [Pp] [Qq] [Rr] [Ss] [Tt] [Uu] [Vv] [Ww] [Xx] [Yy] [Zz]


       zshmisc - everything and then some


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

              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
       pipeline  is  preceded  by  `!'  in which case the value is the logical
       inverse of the value of the last command.  For example,

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

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

       If a pipeline is preceded by `coproc', it is executed as a coprocess; a
       two-way pipe is established between it and the parent shell.  The shell
       can read from or write to the coprocess by means of the `>&p' and `<&p'
       redirection 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
       ordinary 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
       command  which will be executed if and only if the grep command returns
       a zero status.  If it does not, the value of the sublist is that return
       status,  else  it is the status returned by the print (almost certainly

       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
       whatsoever, including the  complex  commands  below;  this  is  implied
       wherever  the  word `list' appears in later descriptions.  For example,
       the commands in a shell function form a special sort of list.


       A simple command may be preceded by a precommand modifier,  which  will
       alter  how  the  command  is  interpreted.   These  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
              special properties of them are suppressed. The -p flag causes  a
              default  path  to be searched instead of that in $path. With the
              -v flag, command is  similar  to  whence  and  with  -V,  it  is
              equivalent 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
              interpreted  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,
              executing list each time.  If the in word is  omitted,  use  the
              positional parameters instead of the words.

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

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

              If  the  list  that  is executed is terminated with ;| the shell
              continues to scan the  patterns  looking  for  the  next  match,
              executing  the corresponding list, and applying the rule for the
              corresponding terminator ;;, ;& 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
              selection until a break or end-of-file is encountered.

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

       { list }
              Execute list.

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

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

              An `error' in this context is a condition such as a syntax error
              which  causes  the  shell  to  abort  execution  of  the current
              function, script, or list.  Syntax errors encountered while  the
              shell  is  parsing  the  code do not cause the always-list to be
              executed.  For 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
              substitution  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
              useful (unless this forms part of an enclosing always block).

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

              The  following  executes  the given code, ignoring any errors it
              causes.  This is an  alternative  to  the  usual  convention  of
              protecting code by executing it in a 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 between the left and
              right parentheses when there is a single word;   otherwise,  the
              parentheses  will  be  treated  as forming a globbing pattern in
              that case.

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

       [[ exp ]]
              Evaluates  the conditional expression exp and return a zero exit
              status if it is true.  See the section `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
       commands, in both these cases the test part of the loop  must  also  be
       suitably delimited, such as by `[[ ... ]]' or `(( ... ))', else the end
       of the test will not be recognized.  For  the  for,  repeat,  case  and
       select  commands  no  such special form for the arguments is necessary,
       but the other condition (the special form of  sublist  or  use  of  the
       SHORT_LOOPS option) still applies.

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

                     if [[ -o ignorebraces ]] {
                       print yes

              works, but

                     if true {  # Does not work!
                       print yes

              does not, since the test is not suitably delimited.

       if list sublist
              A short form of the alternate `if'.  The same 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


       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 ! [[ { }

       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
       behaviour can be recovered by setting the option CONTINUE_ON_ERROR.

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

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


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


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

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

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

       Note   also   the   unhelpful   interaction  of  aliases  and  function

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

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

              noglob func() {
                  echo Do something with $*

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


       A  character  may  be  quoted  (that  is,  made to stand for itself) by
       preceding 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
       considered to be entirely quoted.   A  literal  `''  character  can  be
       included in the string by using the `\'' escape.

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

              print ''''

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

       Inside  double  quotes  (""), parameter and command substitution occur,
       and `\' quotes the characters `\', ``', `"', and `$'.


       If a command is followed by & and job control is not active,  then  the
       default  standard  input  for  the command is the empty file /dev/null.
       Otherwise, the environment for the 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
       produces  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
              CLOBBER  option is unset, this causes an error; otherwise, it is
              truncated to zero length.

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

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

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

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

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

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

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

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

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

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

       If  one  of  the above is preceded by a digit, then the file descriptor
       referred to is that specified by the digit instead of the default 0  or
       1.   The order in which 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
       descriptor 2 would be  associated  with  the  terminal  (assuming  file
       descriptor  1  had been) and then file descriptor 1 would be associated
       with file fname.

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

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


       When  the shell is parsing arguments to a command, and the shell option
       IGNORE_BRACES is not set, a different form of redirection  is  allowed:
       instead  of  a  digit  before  the  operator  there  is  a  valid shell
       identifier enclosed  in  braces.   The  shell  will  open  a  new  file
       descriptor  that  is guaranteed to be at least 10 and set the parameter
       named by the 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

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

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

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

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

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

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

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

              cat file >file1 >file2
              cat file1 file2

       Here,  it  is  possible that the second `cat' will not display the full
       contents of file1  and  file2  (i.e.  the  original  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
       command  with  the  given  redirections.   This  is  the  default  when
       emulating sh or ksh.

       Otherwise, if the parameter NULLCMD is set, its value will be used as a
       command  with  the given redirections.  If both NULLCMD and READNULLCMD
       are set, then the value of the 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
       unsuccessful, the shell prints an error message and returns  a  nonzero
       exit status.

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

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


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

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

       The return builtin is used to return from function calls.

       Function  identifiers  can  be  listed  with  the  functions   builtin.
       Functions can be undefined with the unfunction 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
       recommended   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 corresponding 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
              definitions  as well, but those are neither loaded nor executed;
              a file found in this way is searched only for the definition  of

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

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

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

       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
       initialization  and  then  call  the  function defined, the file should
       contain initialization code (which will be executed then discarded)  in
       addition  to a complete function definition (which will be retained for
       subsequent calls to the function), and a call to  the  shell  function,
       including any arguments, at the end.

       For example, suppose the autoload file func contains

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

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

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

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


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

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

              eval "$(functions)"

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

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

              autoload +X myfunc


       If no name is given for a function, it is `anonymous'  and  is  handled
       specially.  Either form of function definition may be used: a `()' with
       no preceding name, or a `function' with an immediately  following  open
       brace.  The function is 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
       closing brace defining  the  function,  hence  if  there  are  none  no
       arguments  (other  than $0) are set.  This is a difference from the way
       other functions are parsed: normal function definitions may be followed
       by  certain  keywords  such as `else' or `fi', which will be treated as
       arguments to anonymous functions, so that a  newline  or  semicolon  is
       needed to force keyword interpretation.

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

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

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

       Note  that  function definitions with arguments that expand to nothing,
       for example `name=; function  $name  {  ...  }',  are  not  treated  as
       anonymous  functions.   Instead,  they  are  treated as normal function
       definitions where the definition 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
       executed  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
       immediately  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 (and the line was
              not discarded from the history buffer), the string that the user
              typed  is passed as the first argument, otherwise it is an empty
              string.  The actual command that  will  be  executed  (including
              expanded  aliases)  is passed in two different forms: the second
              argument is a single-line, size-limited version of  the  command
              (with  things  like  function bodies elided); the third argument
              contains the full text that is being executed.

              Executed when a history line has been  read  interactively,  but
              before  it  is  executed.   The  sole  argument  is the complete
              history 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
              executed, 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
              context  so  that  the history is saved in a different file from
              the that in the global  HISTFILE  parameter.   This  is  handled
              specially:  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
              newline stripped, which is usually the correct behaviour.   Then
              it switches the history context so that the line will be written
              to a history file in the current directory.

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

              Executed at the point where the main  shell  is  about  to  exit
              normally.  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
              execution 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
              executed inside other traps.

              If the option DEBUG_BEFORE_CMD is set (as  it  is  by  default),
              executed  before  each  command;  otherwise  executed after each
              command.   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.
              However, the function is not executed if the command occurred in
              a  sublist followed by `&&' or `||'; only the final command in a
              sublist of this type  causes  the  trap  to  be  executed.   The
              function  TRAPERR  acts  the  same  as TRAPZERR on systems where
              there is no SIGERR (this is the usual case).

       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

       ·      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

       ·      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.

       ·      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
       `suspended',  and  print  another  prompt.  You can then manipulate the
       state of this job, putting it in the background with the bg command, or
       run some other commands and then eventually bring the job back into the
       foreground  with  the  foreground  command  fg.   A  ^Z  takes   effect
       immediately  and is like an interrupt in that pending output and unread
       input are discarded when it is 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
       continue the job the function will no longer  be  part  of  the  parent
       shell, and any variables set by the function will not be visible in the
       parent shell.  Thus the behaviour is different from the case where  the
       function  was never suspended.  Zsh is different from many other shells
       in this regard.

       The same behaviour is found when the shell is  executing  code  as  the
       right  hand  side  of a pipeline or any complex shell construct such as
       if, for, etc., in order that the entire block of code can be managed as
       a  single job.  Background jobs are normally allowed to produce output,
       but this can be disabled by giving the command `stty tostop'.   If  you
       set this tty option, then background jobs will suspend when they try to
       produce output like they do when they try to read 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
       suspended.  This (intentionally) does  not  apply  if  the  command  is
       continued via `kill -CONT', nor when it is continued with bg.

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

              The job with the given number.
              Any job whose command line begins with string.
              Any job whose command line contains string.
       %%     Current job.
       %+     Equivalent to `%%'.
       %-     Previous job.

       The  shell  learns  immediately  whenever  a process changes state.  It
       normally informs you whenever a job becomes blocked so that no  further
       progress  is possible.  If the NOTIFY option is not set, it waits until
       just before it prints  a  prompt  before  it  informs  you.   All  such
       notifications  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
       triggers any trap set for CHLD.

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

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


       The  INT  and  QUIT  signals  for an invoked command are ignored if the
       command is followed by `&' and the MONITOR option is not  active.   The
       shell  itself  always ignores the QUIT 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
       corresponding precision is provided by the compiler and the library.

       The let builtin command takes arithmetic expressions as arguments; each
       is evaluated separately.  Since many of the  arithmetic  operators,  as
       well  as  spaces, require quoting, an alternative form is provided: for
       any command which begins with  a  `((',  all  the  characters  until  a
       matching  `))'  are  treated  as  a  quoted  expression  and arithmetic
       expansion 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 occurred.

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

       Integers can be in bases other than 10.  A leading `0x' or `0X' denotes
       hexadecimal.   Integers may also be of the form `base#n', where base is
       a decimal number between two and thirty-six representing the arithmetic
       base  and  n  is  a 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
       arithmetical 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
       arithmetic  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
       encountered  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
       output base 16, while  x  (assuming  it  does  not  already  exist)  is
       implicitly  typed  by  the arithmetic evaluation, where it acquires the
       output base 8.

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

       When  an  output  base  is  specified  using  the  `[#base]' syntax, an
       appropriate base prefix will be output if necessary, so that the  value
       output  is  valid  syntax  for input.  If the # is doubled, for example
       `[##16]', then no base prefix is 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,
       << >>  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
       evaluated.  Note the  precedence  of  the  bitwise  AND,  OR,  and  XOR

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

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

       Note the precedence of exponentiation in both cases is  below  that  of
       unary   operators,  hence  `-3**2'  evaluates  as  `9',  not  -9.   Use
       parentheses where necessary: `-(3**2)'.  This is 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/mathfunc  may  be  loaded  with  the  zmodload  builtin  to provide
       standard floating point mathematical functions.

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

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

              ((val2 = val1 * 2))

       assigns twice the value of $val1 to the parameter named val2.

       An  internal  integer  representation  of  a  named  parameter  can  be
       specified 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 down to the next integer.

       Likewise, floating  point  numbers  can  be  declared  with  the  float
       builtin; there are two types, differing only in their output format, as
       described for the typeset builtin.  The output format can  be  bypassed
       by using arithmetic 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
       necessary.  In addition, if any  operator  which  requires  an  integer
       (`~',  `&',  `|',  `^',  `%',  `<<',  `>>'  and  their equivalents with
       assignment) is given a floating point argument,  it  will  be  silently
       rounded down to the next integer.

       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

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

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

       -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 `==' form is the  preferred
              one.   The  `=' form is for backward compatibility and should be
              considered obsolete.

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

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

              If the option BASH_REMATCH is not set the scalar 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
              substrings 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,

              If  the option BASH_REMATCH is set the array BASH_REMATCH is set
              to the substring  that  matched  the  pattern  followed  by  the
              substrings  that matched 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
              conditional expressions.

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

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

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

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

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

       Normal  shell  expansion  is  performed on the file, string and pattern
       arguments, but the result of each expansion  is  constrained  to  be  a
       single  word,  similar  to  the  effect  of  double  quotes.   Filename
       generation is not performed on any  form  of  argument  to  conditions.
       However,  pattern  metacharacters are active for the pattern arguments;
       the patterns are the same as those used for  filename  generation,  see
       zshexpn(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
       represented as `!!'.

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

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

       %~     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
              directories in zshexpn(1).

       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

       %x     The name of the file containing the source code currently  being
              executed.   This  behaves  as  %N  except that function and eval
              command 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
              deprecated  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
              strftime(3)  for  more  details.  Various zsh extensions provide
              numbers 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

              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
              strftime()  with  any  leading  `-', present, so the handling is
              system dependent.  Further GNU extensions are not  supported  at

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

       %E     Clear to end of line.

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

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

       %F (%f)
              Start  (stop)  using a different foreground colour, if supported
              by the terminal.  The colour may be specified two  ways:  either
              as  a  numeric  argument,  as normal, or by a sequence in braces
              following the %F, for example %F{red}.  In the latter  case  the
              values  allowed  are  as  described  for  the  fg  zle_highlight
              attribute; see 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
              position  of  the  %G is unimportant.  Negative integers are not

              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.  The test  character  x  may  be  any  of  the

              !      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.
              g      True if the effective gid of the current process is n.
              j      True if the number of jobs is at least n.
              L      True if the SHLVL parameter is at least n.
              l      True  if  at least n characters have already been printed
                     on the current line.
              S      True if the SECONDS parameter is at least n.
              T      True if the time in hours is equal to n.
              t      True if the time in minutes is equal to n.
              v      True if the array psvar has at least n elements.
              V      True  if  element  n  of  the  array  psvar  is  set  and
              w      True if the day of the week is equal to n (Sunday = 0).

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

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

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

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

  All copyrights belong to their respective owners. Other content (c) 2014-2018, GNU.WIKI. Please report site errors to
Page load time: 0.109 seconds. Last modified: November 04 2018 12:49:43.