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zshmisc



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 com­
       mand 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  sepa­
       rated  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 stan­
       dard 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  sec­
       ond.

       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  con­
       trol 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
       value).  If two pipelines are separated by `||', the  sec­
       ond is executed only if the first fails (returns a nonzero
       value).  Both operators have equal precedence and are left
       associative.  The value of the sublist is the value of the
       last pipeline executed.  For example,

       it to finish before executing the next sublist.  If a sub­
       list is terminated by a `&', `&|', or `&!', the shell exe­
       cutes 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  func­
       tion 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 precom­
              mand 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,
              to the corresponding parameters.  If there are more
              names  than  remaining words, the remaining parame­
              ters 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 pat­
              terns is the same as that used for filename genera­
              tion.   See  the section `Filename Generation'.  If
              the list that is executed  is  terminated  with  ;&
              rather  than  ;;,  the  following list is also exe­
              cuted.  This continues until either a list is  ter­
              minated with ;; or the esac is reached.

       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 parame­
              ter  name  is set to the word corresponding to this
              number.  If this line is empty, the selection  list

       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  speci­
              fied  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

              ous 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  dis­
       abled 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.
       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 substitu­
       tion  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 specifi­
       cations.

       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 cre­
              ated.
              dard  output.   If the file does not exist, and the
              CLOBBER option is unset, this causes an error; oth­
              erwise, 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 genera­
              tion 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, `\' fol­
              lowed by a newline is removed, and `\' must be used
              to quote the characters `\', `$', ``' and the first
              character of word.

              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.

       <& 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
              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 redi­
       rections are specified is significant.  The  shell  evalu­
       ates  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 |'.

       For output redirections only,  if  word  is  of  the  form
       `>(list)'  then  the output is piped to the command repre­
       sented 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  speci­
       fied  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 (glob­
       bing).  Thus

              : > *
              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

       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.  How­
       ever, 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  dis­
       play the full contents of file1 and file2 (i.e. the origi­
       nal 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 writ­
       ing 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.
       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 mes­
       sage 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  pro­
       gram.  The shell will execute the specified interpreter on
       operating systems that do not handle this executable  for­
       mat 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  exe­
       cuted  like  commands  with  the arguments passed as posi­
       tional parameters.  (See the section `Command Execution'.)

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

       functions  precompiled  with  the zcompile builtin command
       the flag -U must be provided when the .zwc  file  is  cre­
       ated,  as  the  corresponding information is compiled into
       the latter.

       For each element in fpath, the shell looks for three  pos­
       sible files, the newest of which is used to load the defi­
       nition 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 func­
              tion 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 defini­
              tion for function.

       In  summary, the order of searching is, first, in the par­
       ents 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 func­
       tion  that is sought, the leftmost in the fpath is chosen;
       and third, within a directory, the newer of either a  com­
       piled function or an ordinary function definition is used.

       If the KSH_AUTOLOAD option is set, or  the  file  contains
       file should contain initialization  code  (which  will  be
       executed  then  discarded) in addition to a complete func­
       tion 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 mes­
       sage on the first call, and the other message on the  sec­
       ond 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 `# unde­
       fined' 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

       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 exe­
              cuted (including expanded aliases) is passed in two
              different  forms:  the  second  argument  is a sin­
              gle-line, size-limited version of the command (with
              things  like  function  bodies  elided);  the third
              argument contains the full text that is being  exe­
              cuted.

       TRAPNAL
              If defined and non-null, this function will be exe­
              cuted 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  SIG­
              NAL.

       TRAPDEBUG
              Executed after each command.

       TRAPEXIT
              Executed  when the shell exits, or when the current
              function exits if defined inside a function.

       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  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 envi­
       ronment.  Apart from the difference in  calling  procedure
       and  the  fact  that the function form appears in lists of
       functions, the forms

              TRAPNAL() {
               # code
              }

       and
              [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 con­
       trol 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 com­
       mand, or run some other commands and then eventually bring
       the job back into the foreground with the foreground  com­
       mand  fg.   A  ^Z  takes effect immediately and is like an
       interrupt in that pending output and unread input are dis­
       carded 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
       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.  Otherwise, signals have the values
       inherited by the shell from its parent (but see the  TRAP­
       NAL special functions in the section `Functions').


ARITHMETIC EVALUATION

       The  shell  can  perform integer and floating point arith­
       metic, 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 quot­
       ing, 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  "..."'.
       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  hex­
       adecimal).   The  base# may also be omitted, in which case
       base 10 is used.  For  backwards  compatibility  the  form
       `[base]n' is also accepted.

              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 hexadeci­
       mal and octal, and these formats are always understood  on
       input.

       When  an output base is specified using the `[#base]' syn­
       tax, an appropriate base prefix will be output  if  neces­
       sary,  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 param­
       eter 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
       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 ASCII
       value of this character and  an  expression  of  the  form
       `#foo' gives the ASCII value of the first character of the
       value of the parameter foo.  Note that this  is  different
       from  the expression `$#foo', a standard parameter substi­
       tution 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 sub­
       stitution  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 with­
       out 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.


CONDITIONAL EXPRESSIONS

       A conditional expression is used with the [[ compound com­
       mand 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 let­
              ter  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 pro­
              cess.

       -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

       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
       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  defi­
              nition 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  code 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-interac­
              tively.

       %d
       %/     Present working directory ($PWD).   If  an  integer
              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  sec­
              onds.

       %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.

              string within the braces should not change the cur­
              sor 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 fol­
              lowing  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 privi­
                     leges.
              #      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.
              c
              .
              ~      True  if  the  current  path,  with   prefix
                     replacement, has at least n 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.
              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 stan­
              dard print processing, in  addition  to  any  back­
              slashes  removed  by  a  double quoted string:  the
              worst case is therefore `print -P "%<\\\\<<..."'.

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

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

zsh 4.1.1                 June 18, 2003                ZSHMISC(1)
  

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