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ZSHMISC(1)                                                          ZSHMISC(1)



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 environ-
       ment 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 sepa-
       rated 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 termi-
       nated 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 excep-
       tion 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 environ-
              ment 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 'Arith-
              metic 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 evalu-
              ate 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 genera-
              tion.  See the section 'Filename Generation'.

              If the list that is executed is terminated with ;& rather than ;;, the  fol-
              lowing  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 num-
              ber.  If this line is empty, the selection list is  printed  again.   Other-
              wise,  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 exe-
              cuted 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  con-
              structed 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  refer-
              enced  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 form-
              ing 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 omit-
              ted, 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  neces-
       sary,  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 men-
              tioned above.

       until list { list }
              An alternative form of until.  Note the limitations on the form of list men-
              tioned above.

       repeat word sublist
              This is a short form of repeat.

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

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

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

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

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

COMMENTS
       In 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 his-
       tory expansion.  Therefore, if an alias is defined for the word foo,  alias  expan-
       sion  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 automat-
       ically 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 defintions, this causes the following com-
       mand 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 stan-
       dard 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;  oth-
              erwise, the file is created.

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

       <<[-] word
              The shell input is read up to a line that is the same  as  word,  or  to  an
              end-of-file.   No parameter expansion, command substitution or filename gen-
              eration is performed on word.  The resulting document, called  a  here-docu-
              ment, 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/out-
              put.

       >& word
       &> word
              (Except  where  '>& word' matches one of the above syntaxes; '&>' can always
              be used to avoid this ambiguity.)  Redirects both standard output and  stan-
              dard  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  descrip-
       tor 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  parame-
       ter  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 exe-
       cuted 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 sub-
       jected 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  exe-
       cuted 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 exe-
       cuted, the shell searches for its definition using the elements of the fpath  vari-
       able.  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  func-
       tions 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  con-
              tain  the definitions for all functions in the directory named element.  The
              file is treated in the same manner as a directory containing files for func-
              tions  and  is searched for the definition of the function.   If the defini-
              tion 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 explic-
              itly given by the user), element is searched for the definition of the func-
              tion  without  comparing its age to that of other files; in fact, there does
              not need to be any directory named element without the suffix.  Thus includ-
              ing  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  dis-
       carded 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 func-
       tion 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 sec-
              onds,  just  before  a  prompt.  Note that if multiple functions are defined
              using the array periodic_functions only one period is applied  to  the  com-
              plete  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-exe-
              cuted 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 argu-
              ment, otherwise it is an empty string.  The actual command that will be exe-
              cuted  (including  expanded  aliases)  is passed in two different forms: the
              second argument is a 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 ter-
              minating 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 exe-
              cuted 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 HIST-
              FILE parameter.  This is handled specially: the history context is automati-
              cally 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 nor-
              mally.  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  pro-
              vided 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 func-
              tion 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 (con-
       trol-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  indi-
       cate  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 fore-
       ground 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  termi-
       nal.   Background jobs are normally allowed to produce output, but this can be dis-
       abled by giving the command 'stty tostop'.  If you set this tty option, then  back-
       ground 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 contin-
       ued 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  fol-
       lowed 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 pre-
       cision 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  cor-
       responding 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 hexadeci-
       mal.  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 recom-
       mended 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  evalua-
       tion, 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 expres-
       sions 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 opera-
       tors, 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 func-
       tion decides if the args is used as a string or a comma-separated  list  of  arith-
       metic  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  arith-
       metic 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  assign-
       ment  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 subex-
              presssions.  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  sub-
              string  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  charac-
              ters.

       string1 > string2
              true  if  string1  comes after string2 based on ASCII value of their charac-
              ters.

       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 argu-
       ment  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 parame-
       ter 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  parame-
       ter 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  sup-
              ported,  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  cur-
              rently  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 contrac-
              tion 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 charac-
              ters  are  provided to strftime() with any leading '-', present, so the han-
              dling 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 termi-
              nal.  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_high-
              light  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 alter-
              nate 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 out-
              put 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 arbitrar-
              ily-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 ele-
                     ments.
              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 cur-
                     rent 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 direc-
              tory 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,  how-
              ever,  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 trun-
              cation 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 exam-
              ple, the prompt '%10<...<%~%<<%# ' will print a truncated representation  of
              the current directory, followed by a '%' or '#', followed by a space.  With-
              out the '%<<', those two characters would be included in the  string  to  be
              truncated.



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