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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 sepa-
       rated from the next by '|' or '|&'.  Where commands are separated by '|', the standard output of the first com-
       mand  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'  redi-
       rection  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 dif-
       ference 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 prop-
              erties  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 modi-
              fier, 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 exe-
              cuting 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 execu-
              tion 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.  Nor-
              mally, 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  con-
       cern.

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

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

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

              works, but

                     if true {  # Does not work!
                       print yes
                     }

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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

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

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

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

COMMENTS
       In 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;  comple-
       tion 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 defintions, 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 sin-
       gle 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 descrip-
       tors 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  cre-
              ated.

       > 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 CLOB-
              BER 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  char-
              acter 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 ref-
              erences 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 ambigu-
              ity.)   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  sec-
              tion 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 evalu-
       ates each redirection in terms of the (file descriptor, file) association at the time of evaluation.  For exam-
       ple:

              ... 1>fname 2>&1

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

       If  instead  of  a  digit  one of the operators above is preceded by a valid identifier enclosed in braces, the
       shell will open a new file descriptor that is guaranteed to be at least 10 and set the parameter named  by  the
       identifier  to the file descriptor opened.  No whitespace is allowed between the closing brace and the redirec-
       tion character.  The option IGNORE_BRACES must not be set.  For example:

              ... {myfd}>&1

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

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

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

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

       Note that this mechanism merely allocates or closes a file descriptor; it does  not  perform  any  redirections
       from  or  to  it.   It is usually convenient to allocate a file descriptor prior to use as an argument to exec.
       The following shows a typical sequence of allocation, use, and closing of a file descriptor:

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

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

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

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

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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to 'cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo foo > bar > baz

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

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

              cat file >file1 >file2
              cat file1 file2

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

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

              { cat file } >file >file2

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


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

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

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

       Otherwise, if the parameter NULLCMD is set, its value will be used as a command with  the  given  redirections.
       If  both NULLCMD and READNULLCMD are set, then the value of the latter will be used instead of that of the for-
       mer 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 func-
       tion 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  func-
       tions  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  Execu-
       tion'.)

       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 cre-
       ated, 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 con-
              taining 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), ele-
              ment 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 ele-
              ment such as '/usr/local/funcs.zwc' in fpath will speed up the search for functions, with the  disadvan-
              tage 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  initial-
       ization, 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 sub-
       sequent 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  initializa-
       tion 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 defi-
       nition 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)' and the parameter list passed to the function is empty.  Note that this means the argu-
       ment list of any enclosing script or function is hidden.  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 pro-
       vide their own local variable scope.

       For example,

              variable=outside
              function {
                local variable=inside
                print "I am $variable"
              }
              print "I am $variable"

       outputs the following:

              I am inside
              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  '_func-
       tions' 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 com-
              mand 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 con-
              tains 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  SIG-
              NAL.

              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  sig-
              nal.

                     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  func-
              tion exiting.

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

       The functions beginning 'TRAP' may alternatively be defined with the trap builtin:  this may be preferable  for
       some  uses,  as  they are then run in the environment of the calling process, rather than in their own function
       environment.  Apart from the difference in calling procedure and the fact that the  function  form  appears  in
       lists of functions, the forms

              TRAPNAL() {
               # code
              }

       and

              trap '
               # code
              ' NAL

       are equivalent.

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

              [1] 1234

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

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

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

       A job being run in the background will suspend if it tries to read from the terminal.  Background jobs are nor-
       mally 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 pro-
       cess 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 sus-
       pended (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 run-
       ning 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 substitu-
       tion 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 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 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 nec-
       essary, 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 prece-
       dence):

       + - ! ~ ++ --
              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 mathemati-
       cal  functions by default, but the module zsh/mathfunc may be loaded with the zmodload builtin to provide stan-
       dard 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 con-
       tents 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 arith-
       metic 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  conse-
       quently  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  let-
              ter option name.  (See the section 'Specifying Options'.)

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

       -r file
              true if file exists and is readable by current 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 com-
              patibility 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 '${var[$MBE-
              GIN,$MEND]}' is identical to '$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  pat-
              tern 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.  File 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 substi-
       tution 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 lit-
       eral '!' 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 capa-
              bilities 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 inte-
              ger 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 lead-
              ing 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 exten-
              sions 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 spec-
              ified 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 cur-
              sor 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 replac-
              ing 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 representa-
              tion of the current directory, followed by a '%' or '#', followed by a space.  Without the '%<<',  those
              two characters would be included in the string to be truncated.



zsh 4.3.11                     December 20, 2010                    ZSHMISC(1)