Home Man
Today's Posts

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

CentOS 7.0 - man page for zshmisc (centos section 1)

ZSHMISC(1)									       ZSHMISC(1)

       zshmisc - everything and then some

       A  simple  command is a sequence of optional parameter assignments followed by blank-sepa-
       rated 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 | sed 's/foo/bar/'

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

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

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

	      dmesg | grep panic && print yes

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

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

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

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

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

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

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

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

	      The -c option clears the environment.

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

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

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

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

       A complex command in zsh is one of the following:

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

       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 cor-
	      responding parameters.  If there are more names than remaining words, the remaining
	      parameters are each set to the empty string.  Execution of the loop ends when there
	      is no remaining word to assign to the first name.  It is only possible  for  in  to
	      appear as the first name in the list, else it will be treated as marking the end of
	      the list.

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

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

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

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

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

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

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

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

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

	      An error condition can be tested	and  reset  with  the  special	integer  variable
	      TRY_BLOCK_ERROR.	 Outside  an  always-list the value is irrelevant, but it is ini-
	      tialised 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 sub-

			 # 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 sta-
	      tistics about the shell process and its children.

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

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

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

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

		     if [[ -o ignorebraces ]] {
		       print yes

	      works, but

		     if true {	# Does not work!
		       print yes

	      does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
	      This is a short form of repeat.

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

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

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

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

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

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

       Fatal errors found in non-interactive shells include:
       Failure to parse shell options passed when invoking the shell
       Failure to change options with the set builtin
       Parse errors of all sorts, including failures to parse
	      mathematical expressions
       Failures to set or modify variable behaviour with typeset,
	      local, declare, export, integer, float
       Execution of incorrectly positioned loop control structures
	      (continue, break)
       Attempts to use regular expression with no regular expression
	      module available
       Disallowed operations when the RESTRICTED options is set
       Failure to create a pipe needed for a pipeline
       Failure to create a multio
       Failure to autoload a module needed for a declared shell feature
       Errors creating command or process substitutions
       Syntax errors in glob qualifiers
       File generation errors where not caught by the option BAD_PATTERN
       All bad patterns used for matching within case statements
       File generation failures where not caused by NO_MATCH or
       All file generation errors where the pattern was used to create a
       Memory errors where detected by the shell
       Invalid subscripts to shell variables
       Attempts to assign read-only variables
       Logical errors with variables such as assignment to the wrong type
       Use of invalid variable names
       Errors in variable substitution syntax
       Failure to convert characters in $'...' expressions
	      similar options

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

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

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

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

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

	      alias echobar='echo bar'; echobar

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

       Note also the unhelpful interaction of aliases and function definitions:

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

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

	      noglob func() {
		  echo Do something with $*

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

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

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

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

	      print ''''

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

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

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

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

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

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

	      ... {myfd}>&1

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

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

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

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

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

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

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

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

       If  the	user  tries to open a file descriptor for writing more than once, the shell opens
       the file descriptor as a pipe to a process that copies its input to all the specified out-
       puts, 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 re-
       direction; thus

	      date >foo | cat

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

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

	      : > *

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

	      echo exit 0 >> *.sh

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

	      sort <foo <fubar

       or even

	      sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

	      cat bar | sort <foo

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

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

	      echo foo > bar > baz

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

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

	      cat file >file1 >file2
	      cat file1 file2

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

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

	      { cat file } >file >file2

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

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

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

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

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

	      < file

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

       If a command name contains no slashes, the shell attempts to locate it.	If there exists a
       shell function by that name, the function is invoked as described in  the  section  `Func-
       tions'.	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 exe-
       cutable 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 inter-
       preter for the program.	The shell will execute the  specified  interpreter  on	operating
       systems that do not handle this executable format in the kernel.

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

       Shell  functions  are defined with the function reserved word or the special syntax `func-
       name ()'.  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  work-
       ing directory with the caller.  A trap on EXIT set inside a function is executed after the
       function completes in the environment of the caller.

       The return builtin is used to return from function calls.

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

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

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

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

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

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

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

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

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

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

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

       Otherwise, the function body (with no surrounding `funcname() {...}') is taken to  be  the
       complete  contents  of the file.  This form allows the file to be used directly as an exe-
       cutable 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,  includ-
       ing any arguments, at the end.

       For example, suppose the autoload file func contains

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

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

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

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


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

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

	      eval "$(functions)"

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

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

	      autoload +X myfunc

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

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

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

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

       For example,

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

       outputs the following:

	      I am inside with arguments this and that
	      I am outside

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

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

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

       chpwd  Executed whenever the current working directory is changed.

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

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

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

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

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

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

	      The following example function first adds the history line to  the  normal  history
	      with  the  newline  stripped,   which  is  usually  the correct behaviour.  Then it
	      switches the history context so that the line will be written to a history file  in
	      the current directory.

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

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

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

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

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

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

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

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

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

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

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

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

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

	      TRAPNAL() {
	       # code

       ('function traps') and

	      trap '
	       # code
	      ' NAL

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

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

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

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

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

	      [1] 1234

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

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

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

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

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

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

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

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

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

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

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

       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 sec-
       ond time; the suspended jobs will be terminated, and the  running  jobs	will  be  sent	a
       SIGHUP signal, if the HUP option is set.

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

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

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

       The let builtin command takes arithmetic expressions as arguments; each is evaluated sepa-
       rately.	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  per-
       formed as for an argument of let.  More precisely, `((...))' is equivalent to `let "..."'.
       The return status is 0 if the arithmetic value of the expression is non-zero, 1 if  it  is
       zero, and 2 if an error occurred.

       For example, the following statement

	      (( val = 2 + 1 ))

       is equivalent to

	      let "val = 2 + 1"

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

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

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

       It  is  also  possible  to specify a base to be used for output in the form `[#base]', for
       example `[#16]'.  This is used when outputting arithmetical substitutions or when  assign-
       ing  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.	All  numeric  parts  (before  and
       after  the  decimal  point  and in the exponent) may contain underscores after the leading
       digit for visual guidance; these are ignored in computation.

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

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

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

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

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

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

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

       Mathematical functions can be called with the  syntax  `func(args)',  where  the  function
       decides	if  the  args is used as a string or a comma-separated list of arithmetic expres-
       sions. 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 han-
       dling 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 inte-
       ger results in rounding down to the next integer.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ( exp )
	      true if exp is true.

       ! exp  true if exp is false.

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

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

       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 dou-
       ble  quotes.   Filename generation is not performed on any form of argument to conditions.
       However, pattern metacharacters are active for the pattern arguments; the patterns are the
       same as those used for filename generation, see zshexpn(1), but there is no special behav-
       iour 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  inte-
       ger,  then  the	test  applied  to the open file whose descriptor number is n, even if the
       underlying system does not support the /dev/fd directory.

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

       For example, the following:

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

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

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

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

       Certain escape sequences may be recognised in the prompt string.

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

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

   Special characters
       %%     A `%'.

       %)     A `)'.

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

       %M     The full machine hostname.

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

       %n     $USERNAME.

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

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

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

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

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

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

       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

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

       %C     Trailing component of the current working directory.  An integer may follow the `%'
	      to  get  more  than  one component.  Unless `%C' is used, tilde contraction is per-
	      formed 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 lat-
	      ter two sequences.

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

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

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

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

       %w     The date in day-dd format.

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

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

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

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

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

       %E     Clear to end of line.

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

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

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

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

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

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

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

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

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

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

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

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

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

	      Specifies  truncation behaviour for the remainder of the prompt string.  The third,
	      deprecated, form is equivalent to `%xstringx', i.e. x  may  be  `<'  or  `>'.   The
	      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 `>' trun-
	      cate  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 back-
	      slashes 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 trunca-
	      tion 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 `#', fol-
	      lowed by a space.  Without the `%<<', those two characters would be included in the
	      string to be truncated.

zsh 5.0.2				December 21, 2012			       ZSHMISC(1)

All times are GMT -4. The time now is 04:37 AM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
Show Password

Not a Forum Member?
Forgot Password?