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zshmisc(1)                                                          zshmisc(1)


       zshmisc - everything and then some


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

              echo foo

       is a simple command with arguments.

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

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

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

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

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

              dmesg | grep panic && print yes

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

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

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


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

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

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

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

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

              The -c option clears the environment.

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

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

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

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


       A complex command in zsh is one of the following:

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

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

              More than one parameter name  can  appear  before  the  list  of
              words.  If N names are given, then on each execution of the loop
              the next N words are assigned to the  corresponding  parameters.
              If  there  are  more  names  than remaining words, the remaining
              parameters are each set to the empty string.  Execution  of  the
              loop ends when there is no remaining word to assign to the first
              name.  It is only possible for in to appear as the first name in
              the  list,  else  it  will  be treated as marking the end of the

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

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

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

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

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

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

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

              If the list that is executed is terminated  with  ;|  the  shell
              continues  to scan the patterns looking for the next match, exe-
              cuting the corresponding list, and applying  the  rule  for  the
              corresponding  terminator  ;;,  ;& or ;|.  Note that word is not
              re-expanded; all applicable patterns are tested  with  the  same

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

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

       { list }
              Execute list.

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

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

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

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

              Regardless  of TRY_BLOCK_ERROR, after the end of always-list the
              normal shell status $? is the value returned  from  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 pro-
              tecting code by executing it in a subshell.

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

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

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

              If  the  option  SH_GLOB  is  set  for  compatibility with other
              shells, then whitespace may appear between 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  parame-
              ter.   If  pipeline is omitted, print statistics about the shell
              process and its children.

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


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

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

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

                     if [[ -o ignorebraces ]] {
                       print yes

              works, but

                     if true {  # Does not work!
                       print yes

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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


       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  behav-
       iour 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  stan-


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


       Every 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  com-
       mand),  or  if the alias is global.  If the text ends with a space, the
       next word in the shell input is treated as though it  were  in  command
       position  for  purposes  of alias expansion.  An alias is defined using
       the alias builtin; global aliases may be defined using the -g option to
       that builtin.

       Alias  expansion  is done on the shell input before any other expansion
       except history expansion.  Therefore, if an alias is  defined  for  the
       word  foo,  alias expansion may be avoided by quoting part of the word,
       e.g. \foo.  Any form of quoting works, although  there  is  nothing  to
       prevent  an  alias  being  defined  for the quoted form such as \foo as
       well.  For use with completion, which would remove an initial backslash
       followed  by  a character that isn't special, it may be more convenient
       to quote the word by starting with a single quote, i.e.  'foo;  comple-
       tion 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 `.'.  Con-
       sequently,  use  of  functions  rather  than  aliases is recommended in
       non-interactive code.

       Note also the unhelpful interaction of  aliases  and  function  defini-

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

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

              noglob func() {
                  echo Do something with $*

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


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

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

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

              print ''''

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

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


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

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

       < word Open file word for reading as standard input.

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

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

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

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

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

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

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

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

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

       <<< word
              Perform shell expansion on word and pass the result to  standard
              input.  This is known as a here-string.  Compare the use of word
              in here-documents above,  where  word  does  not  undergo  shell

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

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

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

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

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

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

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

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

              ... 1>fname 2>&1

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

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

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


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

              ... {myfd}>&1

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

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

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

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

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

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

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

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


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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo 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  com-
       mand  with  the given redirections.  This is the default when emulating
       sh or ksh.

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

              < file

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


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

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

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

       If  no  external command is found but a function command_not_found_han-
       dler exists the shell executes this  function  with  all  command  line
       arguments.   The  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 com-
       mand, hence changes to directories,  shell  parameters,  etc.  have  no
       effect on the main shell.


       Shell functions are defined with the function reserved word or the spe-
       cial syntax `funcname ()'.  Shell functions  are  read  in  and  stored
       internally.  Alias names are resolved when the function is read.  Func-
       tions are executed like commands with the  arguments  passed  as  posi-
       tional parameters.  (See the section `Command Execution'.)

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

       The return builtin is used to return from function calls.

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


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

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

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

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

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

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

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

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

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

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

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

       For example, suppose the autoload file func contains

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

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

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

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


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

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

              eval "$(functions)"

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

       To load the definition of an autoloaded function myfunc without execut-
       ing myfunc, use:

              autoload +X myfunc


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

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

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

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

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

       Note  that  function definitions with arguments that expand to nothing,
       for example `name=; function $name { ... }', are not treated as  anony-
       mous  functions.   Instead, they are treated as normal function defini-
       tions where the definition is silently discarded.


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

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

       chpwd  Executed whenever the current working directory is changed.

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

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

              Executed just after a command has been read and is about  to  be
              executed.   If the history mechanism is active (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 his-
              tory line  (so  that  any  terminating  newline  will  still  be

              If any of the hook functions return a non-zero value the history
              line will not be saved, although it lingers in the history until
              the  next line is executed allow you to reuse or edit it immedi-

              A hook function may call `fc -p ...' to switch the history  con-
              text  so  that the history is saved in a different file from the
              that in the global HISTFILE parameter.   This  is  handled  spe-
              cially:  the history context is automatically restored after the
              processing of the history line is finished.

              The following example function 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

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

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

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

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

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

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

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

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

              The  functions  TRAPZERR,  TRAPDEBUG and TRAPEXIT are never exe-
              cuted inside other traps.

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

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

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

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

              TRAPNAL() {
               # code

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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


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

              [1] 1234

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

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

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

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

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

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

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

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

              The job with the given number.
              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 nor-
       mally  informs  you  whenever  a job becomes blocked so that no further
       progress is possible.  If the NOTIFY option is not set, it waits  until
       just before it prints a prompt before it informs you.  All such notifi-
       cations are sent directly to the terminal, not to the  standard  output
       or standard error.

       When  the  monitor mode is on, each background job that completes trig-
       gers any trap set for CHLD.

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

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


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


       The shell can perform integer and  floating  point  arithmetic,  either
       using the builtin let, or via a substitution of the form $((...)).  For
       integers, the shell is usually compiled to use 8-byte  precision  where
       this is available, otherwise precision is 4 bytes.  This can be tested,
       for example, by giving the command `print - $(( 12345678901 ))'; if the
       number  appears unchanged, the precision is at least 8 bytes.  Floating
       point arithmetic always uses the `double'  type  with  whatever  corre-
       sponding precision is provided by the compiler and the library.

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

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

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

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

       It is also possible to specify a base to be used for output in the form
       `[#base]', for example `[#16]'.  This is used  when  outputting  arith-
       metical  substitutions  or  when assigning to scalar parameters, but an
       explicitly defined integer or floating  point  parameter  will  not  be
       affected.   If  an  integer variable is implicitly defined by an arith-
       metic expression, any base specified in this way will  be  set  as  the
       variable's  output  arithmetic  base  as if the option `-i base' to the
       typeset builtin had been used.  The expression has no precedence and if
       it occurs more than once in a mathematical expression, the last encoun-
       tered is used.  For clarity it is recommended that  it  appear  at  the
       beginning of an expression.  As an example:

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

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

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

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

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

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

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

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

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

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

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

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

       An expression of the form `##x' where x is any character sequence  such
       as  `a',  `^A',  or  `\M-\C-x' gives the value of this character and an
       expression of the form `#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 dif-
       ferent 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  speci-
       fied  with  the integer builtin.  Arithmetic evaluation is performed on
       the value of each assignment to a named parameter declared  integer  in
       this  manner.   Assigning a floating point number to an integer results
       in rounding 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 neces-
       sary.  In addition, if any operator which  requires  an  integer  (`~',
       `&',  `|',  `^', `%', `<<', `>>' and their equivalents with assignment)
       is given a floating point argument, it will be silently rounded 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 expres-

       -a file
              true if file exists.

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

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

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

       -e file
              true if file exists.

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

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

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

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

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

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

       -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  vari-
              ables are changed if the matching fails.

              If the option BASH_REMATCH is not set the scalar parameter MATCH
              is set to the substring that matched the pattern and the integer
              parameters  MBEGIN  and  MEND to the index of the start and end,
              respectively, of the match in string, such  that  if  string  is
              contained in variable var the expression `${var[$MBEGIN,$MEND]}'
              is identical to `$MATCH'.  The setting of the option  KSH_ARRAYS
              is  respected.   Likewise,  the  array  match is set to the sub-
              strings that matched parenthesised subexpressions and the arrays
              mbegin  and  mend to the indices of the start and end positions,
              respectively, of the substrings within string.  The  arrays  are
              not  set  if  there  were no parenthesised subexpresssions.  For
              example, if the string `a short string' is matched  against  the
              regular   expression   `s(...)t',   then  (assuming  the  option
              KSH_ARRAYS is not set) MATCH, MBEGIN and MEND are `short', 3 and
              7,  respectively,  while match, mbegin and mend are single entry
              arrays containing the strings `hor', `4' and `6, respectively.

              If the option BASH_REMATCH is set the array BASH_REMATCH is  set
              to  the  substring that matched the pattern followed by the sub-
              strings that matched  parenthesised  subexpressions  within  the

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

       Normal shell expansion is performed on the  file,  string  and  pattern
       arguments, but the result of each expansion is constrained to be a sin-
       gle word, similar to the effect of double quotes.  Filename  generation
       is  not performed on any form of argument to conditions.  However, pat-
       tern 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 repre-
       sented as `!!'.

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


   Special characters
       %%     A `%'.

       %)     A `)'.

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

       %M     The full machine hostname.

       %m     The hostname up to the first `.'.  An integer may follow the `%'
              to  specify  how  many  components  of the hostname are desired.
              With a negative integer, trailing components of the hostname are

       %n     $USERNAME.

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

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

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

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

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

       %~     As %d and %/, but if the current working directory has  a  named
              directory as its prefix, that part is replaced by a `~' followed
              by the name of the directory.  If it  starts  with  $HOME,  that
              part is replaced by a `~'.

       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

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

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

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

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

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

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

       %w     The date in day-dd format.

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

              string  is  formatted  using  the  strftime function.  See strf-
              time(3) for more details.  Various zsh extensions  provide  num-
              bers  with  no  leading  zero or space if the number is a single

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

              The GNU extension that a `-' between the % and the format  char-
              acter  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 strf-
              time() with any leading `-', present, so the handling is  system
              dependent.  Further GNU extensions are not supported at present.

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

       %E     Clear to end of line.

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

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

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

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

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

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

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

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

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


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

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

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

              !      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 dis-
              played 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  exam-
              ple,  if  the  current  directory  is  `/home/pike',  the prompt
              `%8<..<%/' will expand to `..e/pike'.  In this string, the  ter-
              minating  character (`<', `>' or `]'), or in fact any character,
              may be quoted by a preceding `\'; note when using print -P, how-
              ever, that this must be doubled as the string is also subject to
              standard  print  processing,  in  addition  to  any  backslashes
              removed  by a double quoted string:  the worst case is therefore
              `print -P "%<\\\\<<..."'.

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

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

zsh 5.0.2                      December 21, 2012                    zshmisc(1)

Mac OS X 10.9 - Generated Mon Oct 14 06:06:13 CDT 2013
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Individual documents may contain additional copyright information.