Provided by: zsh_4.3.4-24ubuntu1_i386 bug

NAME

       zshmisc - everything and then some

SIMPLE COMMANDS & PIPELINES

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

PRECOMMAND MODIFIERS

       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.

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

       nocorrect
              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.

       exec   The command is executed in the parent shell without forking.

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

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

COMPLEX COMMANDS

       A complex command in zsh is one of the following:

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

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

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

       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’.

              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  preceeding
              closing brace and the always.

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

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

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

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

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

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

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

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

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

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

ALTERNATE FORMS FOR COMPLEX COMMANDS

       Many of zsh’s complex commands have alternate forms.  These  particular
       versions of complex commands should be considered deprecated and may be
       removed in the future.  The versions in the previous section should  be
       preferred instead.

       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 above.

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

       repeat word sublist
              This is a short form of repeat.

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

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

RESERVED WORDS

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

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

       Additionally,  ‘}’  is  recognized in any position if the IGNORE_BRACES
       option is not set.

COMMENTS

       In  noninteractive  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.

ALIASING

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

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

QUOTING

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

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

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

              print ’’’’

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

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

REDIRECTION

       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.

       <> 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.

       If instead of a digit one of the operators above is preceded by a valid
       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.
       The option IGNORE_BRACES must not be set.  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  following shows a typical sequence of allocation, use, and
       closing of a file descriptor:

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

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

       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).

MULTIOS

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

              date >foo >bar

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

              date >foo | cat

       writes the date to the file ‘foo’, and also pipes it to cat.

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to ‘cat foo fubar | sort’.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo foo > bar > baz

       when MULTIOS is unset will truncate bar, and write ‘foo’ into baz.

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

              cat file >file1 >file2
              cat file1 file2

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

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

              { cat file } >file >file2

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

REDIRECTIONS WITH NO COMMAND

       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.

COMMAND EXECUTION

       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.

FUNCTIONS

       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.

AUTOLOADING FUNCTIONS

       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:

       element.zwc
              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.

       element/function.zwc
              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.

       element/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...

       and

              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

SPECIAL FUNCTIONS

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

       In  the  case  of chpwd, periodic, precmd and preexec it is possible to
       define an array that has the same name 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 (thought it may run at the next opportunity).

       chpwd  Executed whenever the current working directory is changed.

       periodic
              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.

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

       zshexit
              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.

       TRAPNAL
              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 traps.

       TRAPDEBUG
              Executed after each command.

       TRAPEXIT
              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.

       TRAPZERR
              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, as they  are  then
       run in the environment of the calling process, rather than in their own
       function environment.  Apart from the difference in  calling  procedure
       and  the fact that the function form appears in lists of functions, the
       forms

              TRAPNAL() {
               # code
              }

       and

              trap# codeNAL

       are equivalent.

JOBS

       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.  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:

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

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

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

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

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

SIGNALS

       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’).

ARITHMETIC EVALUATION

       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 is always double precision.

       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, and 1 otherwise.

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

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

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

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

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

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

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

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

       An arithmetic expression uses nearly the same syntax,  precedence,  and
       associativity  of  expressions  in  C.   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
       < > <= >=
              comparison
       == !=  equality and inequality
       &&     logical AND
       || ^^  logical OR, XOR
       ? :    ternary operator
       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
              assignment
       ,      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.

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

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

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

              ((val2 = val1 * 2))

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

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

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

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

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

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

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

       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.

CONDITIONAL EXPRESSIONS

       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’.)

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

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

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

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

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

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

       Normal  shell  expansion  is  performed on the file, string and pattern
       arguments, but the result of each expansion  is  constrained  to  be  a
       single  word, similar to the effect of double quotes.  However, pattern
       metacharacters are active for the pattern arguments; the  patterns  are
       the  same  as  those  used for filename generation, see zshexpn(1), but
       there is no special behaviour of ‘/’ nor  initial  dots,  and  no  glob
       qualifiers are allowed.

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

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

       For example, the following:

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

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

PROMPT EXPANSION

       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.  Some escapes take an optional integer
       argument, which should appear between the ‘%’ and the next character of
       the sequence.  The following escape sequences are recognized:

   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 vectors.

       %?     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.

       %d
       %/     Present working directory ($PWD).  If  an  integer  follows  the
              ‘%’,  it  specifies  a  number of trailing components of $PWD 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 $PWD has a named directory as its prefix,
              that part is replaced by a ‘~’  followed  by  the  name  of  the
              directory.   If it starts with $HOME, that part is replaced by a
              ‘~’.

       %h
       %!     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.

       %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.

       %c
       %.
       %C     Trailing  component  of  $PWD.  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.

       %t
       %@     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.

       %D{string}
              string  is  formatted  using   the   strftime   function.    See
              strftime(3)  for  more  details.   Three  additional  codes  are
              available:  %f prints the day of the month, like %e but  without
              any  preceding  space  if  the  day is a single digit, and %K/%L
              correspond to %k/%l for the hour of the day (24/12  hour  clock)
              in the same way.

   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.

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

   Conditional substrings
       %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.

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

              The  left  parenthesis may be preceded or followed by a positive
              integer n, which defaults to zero.  A negative integer  will  be
              multiplied  by  -1.   The  test  character  x  may be any of the
              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.
              C
              /      True if the current absolute path has at least n elements
                     relative  to  the root directory, hence / is counted as 0
                     elements.
              c
              .
              ~      True if the current path, with prefix replacement, has at
                     least  n elements relative to the root directory, hence /
                     is counted as 0 elements.
              D      True if the month is equal to n (January = 0).
              d      True if the day of the month is equal to n.
              g      True if the effective gid of the current process is n.
              j      True if the number of jobs is at least n.
              L      True if the SHLVL parameter is at least n.
              l      True if at least n characters have already  been  printed
                     on the current line.
              S      True if the SECONDS parameter is at least n.
              T      True if the time in hours is equal to n.
              t      True if the time in minutes is equal to n.
              v      True if the array psvar has at least n elements.
              w      True if the day of the week is equal to n (Sunday = 0).

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

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

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

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