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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.   For  a  description  of
       assignment, see the beginning of zshparam(1).

       The  first  word  is  the  command  to  be  executed, and the remaining words, if any, are
       arguments to the command.  If a command name is given, the  parameter  assignments  modify
       the  environment of the command when it is executed.  The value of a simple command is its
       exit status, or 128 plus the signal number if terminated by a signal.  For example,

              echo foo

       is a simple command with arguments.

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

              dmesg | grep panic && print yes

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

       A list is a sequence of zero or more sublists, in which each sublist is terminated by `;',
       `&',  `&|',  `&!',  or a newline.  This terminator may optionally be omitted from the last
       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 word.

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

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


       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

       for name ... [ in word ... ] term do list done
              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.

              The term consists of one or more newline or ; which terminate the  words,  and  are
              optional when the `in word' is omitted.

              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 list.

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

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

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

              If the list that is executed is terminated with ;& rather than  ;;,  the  following
              list is also executed.  The rule for the 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 word.

       select name [ in word ... term ] do list done
              where  term  is  one or more newline or ; to terminate the words.  Print the set of
              words, each preceded by a 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 try-list.  This will be non-zero if there was an
              error, even if TRY_BLOCK_ERROR was set to zero.

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

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

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

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

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

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

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

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

       time [ pipeline ]
              The  pipeline is executed, and timing statistics are reported on the standard error
              in the form specified by the TIMEFMT 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.

       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

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

       repeat word sublist
              This is a short form of repeat.

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

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

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


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

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

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


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

       Fatal errors found in non-interactive shells include:

       ·      Failure to parse shell options passed when invoking the 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 similar options

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

       ·      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

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


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


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

       A word is defined as:

       ·      Any plain string or glob pattern

       ·      Any quoted string, using any quoting method (note that the quotes must be  part  of
              the alias definition for this to be eligible)

       ·      Any parameter reference or command substitution

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

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

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

       Alias  expansion  is  done  on  the  shell input before any other expansion except history
       expansion.  Therefore, if an alias is defined for the word foo,  alias  expansion  may  be
       avoided by quoting part of the word, e.g. \foo.  Any form of quoting works, although there
       is nothing to prevent an alias being defined for the quoted form such as \foo as well.

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

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

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

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

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

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

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

              alias echobar='echo bar'; echobar

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

       Note also the unhelpful interaction of aliases and function definitions:

              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

              print ''''

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

       Inside double quotes (""), parameter and command substitution occur, and  `\'  quotes  the
       characters `\', ``', `"', `$', and the first character of $histchars (default `!').


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

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

       < word Open  file  word  for  reading as standard input.  It is an error to open a file in
              this fashion if it does not exist.

       <> 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 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 word.

              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 expansion.

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

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

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

       >& word
       &> word
              (Except where `>& word' matches one of the above 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 readonly.

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

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

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

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

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


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

              date >foo >bar

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

              date >foo | cat

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

       Note that the shell opens all the files to be used in the multio process immediately,  not
       at the point they are about to be written.

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

              date >&1 >output

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

              date >output >&1

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

       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, provided the MULTIOS option is set.  It should be noted
       that each file is opened immediately, not at the point where it is about to be read:  this
       behaviour  differs  from  cat,  so if strictly standard behaviour is needed, cat should be
       used instead.


              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 Hello > bar > baz

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

       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 return status of the function
       becomes  the  status of the command.  If the function wishes to mimic the behaviour of the
       shell when the command is not found, it should print the message `command not found:  cmd'
       to  standard error and return status 127.  Note that the handler is executed in a subshell
       forked to execute an external 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 function.

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

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

       If the KSH_AUTOLOAD option is set, or the file contains only a simple  definition  of  the
       function, the file's contents will be executed.  This will normally define the function in
       question, but may also perform initialization, which is 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

       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 point).

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

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

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

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

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

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

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

                     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 retained.

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

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

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

              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

              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 following:

       ·      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 triggered.

       ·      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.

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

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

       When a command is suspended and continued later with the fg or wait builtins, zsh restores
       tty modes that were in effect when it was 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.
              The last job whose command line begins with string.
              The last job whose command line contains string.
       %%     Current job.
       %+     Equivalent to `%%'.
       %-     Previous job.

       The shell learns immediately whenever a process changes state.  It  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

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

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


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

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


       The shell can perform integer and floating point arithmetic, either using the builtin let,
       or  via  a substitution of the form $((...)).  For integers, the shell is usually compiled
       to use 8-byte precision where this is available, otherwise precision is 4 bytes.  This can
       be  tested, for example, by 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 and  a
       leading  `0b'  or `0B' binary.  Integers may also be of the form `base#n', where base is a
       decimal number between two and thirty-six representing the arithmetic  base  and  n  is  a
       number  in  that base (for example, `16#ff' is 255 in hexadecimal).  The base# may also be
       omitted, in which case base 10 is used.  For backwards compatibility the form `[base]n' is
       also accepted.

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

       It  is  also  possible  to specify a base to be used for output in the form `[#base]', for
       example `[#16]'.   This  is  used  when  outputting  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.

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

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

       outputs `0x1_0000_0000'.

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

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

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

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

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

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

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

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

       + - ! ~ ++ --
              unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement
       << >>  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 operators.

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

       + - ! ~ ++ --
              unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement
       **     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 `#name' gives
       the value of the first character of the contents of the parameter name.  Character  values
       are  according  to  the  character set used in the current locale; for multibyte character
       handling the option MULTIBYTE must  be  set.   Note  that  this  form  is  different  from
       `$#name',  a standard parameter substitution which gives the length of the parameter name.
       `#\' is accepted instead of `##', but its use is deprecated.

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

              ((val2 = val1 * 2))

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

       An  internal integer representation of a named parameter can be 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 towards zero.

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

       Promotion of integer to floating point values is performed where 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  towards
       zero except for `~' which rounds down.

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

       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 types.


       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 expressions:

       -a file
              true if file exists.

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

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

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

       -e file
              true if file exists.

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

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

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

       -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'.)

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

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

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

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

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

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

       -v varname
              true if shell variable varname is set.

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

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

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

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

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

       For example,

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

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

       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


       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


   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 shown.

       %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

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

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

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

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

       %~     As  %d and %/, but if the current working directory starts with $HOME, that part is
              replaced by a `~'. Furthermore, if it has a named directory  as  its  prefix,  that
              part  is  replaced  by a `~' followed by the name of the directory, but only if the
              result is shorter than the full path; see Dynamic and Static named  directories  in

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

       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

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

       %C     Trailing component of the current working directory.  An integer may follow the `%'
              to  get  more  than  one  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 digit:

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

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

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

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

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

       %E     Clear to end of line.

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

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

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

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

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

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

       %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 handled.

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


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

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

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

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

              Specifies truncation behaviour for the remainder of the prompt string.  The  third,
              deprecated,  form  is  equivalent  to  `%xstringx',  i.e. x may be `<' or `>'.  The
              string will be displayed in place of the truncated portion of any string; note this
              does not undergo prompt expansion.

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

              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.  Note that `%-0<<'  is  not  equivalent  to
              `%<<' but specifies that the prompt is truncated at the right margin.

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