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NAME

       zshmisc - everything and then some

SIMPLE COMMANDS & PIPELINES

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

              echo foo

       is a simple command with arguments.

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

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

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

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

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

              dmesg | grep panic && print yes

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

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

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

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.

       builtin
              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.

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

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

COMPLEX COMMANDS

       A complex command in zsh is one of the following:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

ALTERNATE FORMS FOR COMPLEX COMMANDS

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

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

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

                     if [[ -o ignorebraces ]] {
                       print yes
                     }

              works, but

                     if true {  # Does not work!
                       print yes
                     }

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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

RESERVED WORDS

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

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

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

COMMENTS

       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.

ALIASING

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

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

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

              alias echobar='echo bar'; echobar

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

       Note also the unhelpful interaction of aliases and function 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.

QUOTING

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

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

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

              print ''''

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

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

REDIRECTION

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

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

       < word Open file word for reading as standard input.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              ... 1>fname 2>&1

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

       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).

OPENING FILE DESCRIPTORS USING PARAMETERS

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

              ... {myfd}>&1

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

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

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

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

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

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

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

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

MULTIOS

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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo foo > bar > baz

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

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

              cat file >file1 >file2
              cat file1 file2

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

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

              { cat file } >file >file2

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

REDIRECTIONS WITH NO COMMAND

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

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

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

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

              < file

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

COMMAND EXECUTION

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

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

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

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

FUNCTIONS

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

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

       The return builtin is used to return from function calls.

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

AUTOLOADING FUNCTIONS

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

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

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

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

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

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

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

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

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

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

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

       For example, suppose the autoload file func contains

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

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

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

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

       and

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

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

              eval "$(functions)"

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

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

              autoload +X myfunc

ANONYMOUS FUNCTIONS

       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
       `(anon)'.

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

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

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

       For example,

              variable=outside
              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.

SPECIAL FUNCTIONS

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

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

       chpwd  Executed whenever the current working directory is changed.

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

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

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

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

              If any of the hook functions 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
              history  is  saved  in  a  different  file  from  the  that  in the global HISTFILE
              parameter.  This  is  handled  specially:  the  history  context  is  automatically
              restored after the processing of the history line is finished.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              TRAPNAL() {
               # code
              }

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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

JOBS

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

              [1] 1234

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

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

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

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

       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:

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

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

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

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

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

SIGNALS

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

ARITHMETIC EVALUATION

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

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

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              ((val2 = val1 * 2))

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

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

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

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

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

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

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

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

CONDITIONAL EXPRESSIONS

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

       -a file
              true if file exists.

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

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

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

       -e file
              true if file exists.

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

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

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

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

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

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

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

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

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

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

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

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

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

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

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

       For example, the following:

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

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

EXPANSION OF PROMPT SEQUENCES

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

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

       Certain escape sequences may be recognised in the prompt string.

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

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

SIMPLE PROMPT ESCAPES

   Special characters
       %%     A `%'.

       %)     A `)'.

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

       %M     The full machine hostname.

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

       %n     $USERNAME.

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

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

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

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

       %d
       /      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 `~'.

       %h
       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

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

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

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

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

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

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

       %w     The date in day-dd format.

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

       %D{string}
              string is formatted using the strftime function.  See strftime(3) for more details.
              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
              leading zero or space to be stripped is handled  directly  by  the  shell  for  the
              format  characters  d,  f,  H, k, l, m, M, S and y; any other format characters are
              provided to strftime() with any leading `-', present, so  the  handling  is  system
              dependent.  Further GNU extensions are not supported at 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
              Character  Highlighting  in zshzle(1).  This means that numeric colours are allowed
              in the second format also.

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

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

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

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

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

CONDITIONAL SUBSTRINGS IN PROMPTS

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

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

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

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

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

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

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

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