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       zshmisc - everything and then some


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

              echo foo

       is a simple command with arguments.

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

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

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

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

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

              dmesg | grep panic && print yes

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

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

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


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

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

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

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

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

              The -c option clears the environment.

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

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

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

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


       A complex command in zsh is one of the following:

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

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

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

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

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

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

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

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

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

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

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

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

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

       { list }
              Execute list.

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

                     if [[ -o ignorebraces ]] {
                       print yes

              works, but

                     if true {  # Does not work!
                       print yes

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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


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

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

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


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


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

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

       There is a commonly encountered problem with aliases illustrated by the
       following code:

              alias echobar='echo bar'; echobar

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

       Note  also  the  unhelpful  interaction   of   aliases   and   function

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

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

              noglob func() {
                  echo Do something with $*

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


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

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

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

              print ''''

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

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


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

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

       < word Open file word for reading as standard input.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              ... 1>fname 2>&1

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

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

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


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

              ... {myfd}>&1

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

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

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

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

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

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

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

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


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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo foo > bar > baz

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

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

              cat file >file1 >file2
              cat file1 file2

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

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

              { cat file } >file >file2

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


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

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

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

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

              < file

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


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

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

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

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


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

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

       The return builtin is used to return from function calls.

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


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

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

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

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

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

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

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

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

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

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

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

       For example, suppose the autoload file func contains

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

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

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

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


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

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

              eval "$(functions)"

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

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

              autoload +X myfunc


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

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

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

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

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

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


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

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

       chpwd  Executed whenever the current working directory is changed.

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

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

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

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

              If any of the hook functions 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

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

              The  following  example  function 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
              normally.  This is not called by exiting subshells, nor when the
              exec  precommand  modifier  is  used before an external command.
              Also, unlike TRAPEXIT, it is not called when functions exit.

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

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

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

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

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

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

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

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

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

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

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

              TRAPNAL() {
               # code

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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


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

              [1] 1234

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

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

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

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

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

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

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

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

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

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

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

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

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


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


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

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

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

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

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

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

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

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

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

       Floating  point  constants  are recognized by the presence of a decimal
       point or an exponent.  The decimal point may be the first character  of
       the  constant, but the exponent character e or E may not, as it will be
       taken for a parameter name.

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

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

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

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

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

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

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

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

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

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

              ((val2 = val1 * 2))

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

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

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

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

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

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

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

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


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

       -a file
              true if file exists.

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

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

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

       -e file
              true if file exists.

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

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

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

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

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

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

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

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

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

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

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

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       exp1 -eq exp2
              true if exp1 is numerically equal to exp2.

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

       Normal  shell  expansion  is  performed on the file, string and pattern
       arguments, but the result of each expansion  is  constrained  to  be  a
       single  word,  similar  to  the  effect  of  double  quotes.   Filename
       generation is not performed on any  form  of  argument  to  conditions.
       However,  pattern  metacharacters are active for the pattern arguments;
       the patterns are the same as those used for  filename  generation,  see
       zshexpn(1),  but there is no special behaviour of `/' nor initial dots,
       and no glob qualifiers are allowed.

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

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

       For example, the following:

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

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


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

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

       Certain escape sequences may be recognised in the prompt string.

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

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


   Special characters
       %%     A `%'.

       %)     A `)'.

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

       %M     The full machine hostname.

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

       %n     $USERNAME.

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

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

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

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

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

       %~     As  %d  and %/, but if the current working directory 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
              integer may follow the `%' to specify a number of trailing  path
              components  to  show;  zero  means  the  full  path.  A negative
              integer specifies leading components.

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

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

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

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

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

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

       %w     The date in day-dd format.

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

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

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

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

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

       %E     Clear to end of line.

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

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

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

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

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

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

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

              Multiple uses of %G  accumulate  in  the  obvious  fashion;  the
              position  of  the  %G is unimportant.  Negative integers are not

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


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

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

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

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

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

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

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

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