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спецификации, руководства, описания, API
Spec-Zone .ru
спецификации, руководства, описания, API
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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 environment of the command when it is executed.  The value of a simple command
       is its exit status, or 128 plus the signal number if terminated by a signal.  For example,

              echo foo

       is a simple command with arguments.

       A  pipeline  is either a simple command, or a sequence of two or more simple commands where each com-mand command
       mand 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  stan-dard standard
       dard  input  of the next.  The value of a pipeline is the value of the last command, unless the pipe-line pipeline
       line is preceded by `!' in which case the value is the logical inverse of the value of the last  com-mand. command.
       mand.  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  pre-
       ceded 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 suc-ceeds succeeds
       ceeds (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 ter-minated terminated
       minated 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 inter-preted. interpreted.
       preted.   These  modifiers  are  shell  builtin  commands  with the exception of nocorrect which is a
       reserved word.

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

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

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

       exec [ -cl ] [ -a argv_ ]
              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  pre-command precommand
              command  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 posi-tional positional
              tional 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 Genera-tion'. Generation'.
              tion'.

              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 pat-terns patterns
              terns are tested with the same word.

       select name [ in word ... term ] do list done
              where  term  is one or more newline or ; to terminate the words.  Print the set of words, each
              preceded by a number.  If the in word is omitted, use the positional parameters.  The  PROMPT3
              prompt is printed and a line is read from the line editor if the shell is interactive and that
              is active, or else standard input.  If this line consists of the number of one of  the  listed
              words,  then the parameter name is set to the word corresponding to this number.  If this line
              is empty, the selection list is printed again.  Otherwise, the value of the parameter name  is
              set  to  null.   The  contents  of the line read from standard input is saved in the parameter
              REPLY.  list is executed for each selection until a break or end-of-file is encountered.

       ( list )
              Execute list in a subshell.  Traps set by the trap builtin are reset to their  default  values
              while executing list.

       { list }
              Execute list.

       { try-list } always { always-list }
              First  execute try-list.  Regardless of errors, or break, continue, or return commands encoun-tered encountered
              tered 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  erro-neously erroneously
              neously  constructed  if  block  in try-list would cause the shell to abort during parsing, so
              that always-list would not be executed, while an erroneous substitution such as ${*foo*} would
              cause a run-time error, after which always-list would be executed.

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

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

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

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

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

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

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

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

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

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

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

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

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

              works, but

                     if true {  # Does not work!
                       print yes
                     }

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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

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

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

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

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

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

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


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

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

       Alias  expansion  is  done  on  the  shell input before any other expansion except history expansion.
       Therefore, if an alias is defined for the word foo, alias expansion may be avoided by quoting part of
       the  word, e.g. \foo.  Any form of quoting works, although there is nothing to prevent an alias being
       defined for the quoted form such as \foo as well.  For use with completion,  which  would  remove  an
       initial  backslash followed by a character that isn't special, it may be more convenient to quote the
       word by starting with a single quote, i.e. 'foo; completion will automatically add the trailing  sin-gle single
       gle 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  exe-cuted executed
       cuted  it  is  too late to expand the newly defined alias.  This is often a problem in shell scripts,
       functions, and code executed with `source' or  `.'.   Consequently,  use  of  functions  rather  than
       aliases is recommended in non-interactive code.

       Note also the unhelpful interaction of aliases and function definitions:

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

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

              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 `\'.   `\'  fol-lowed followed
       lowed by a newline is ignored.

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

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

              print ''''

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

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

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

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

       < word Open file word for reading as standard input.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       If one of the above is preceded by a digit, then the file descriptor referred to is that specified by
       the  digit  instead of the default 0 or 1.  The order in which redirections are specified is signifi-cant. significant.
       cant.  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 Sub-stitution Substitution
       stitution in zshexpn(1).

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

              ... {myfd}>&1

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

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

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

       If the option CLOBBER is unset, it is an error to open a file descriptor using a  parameter  that  is
       already set to an open file descriptor previously allocated by this mechanism.  Unsetting the parame-ter parameter
       ter 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  redi-rections redirections
       rections  from  or  to it.  It is usually convenient to allocate a file descriptor prior to use as an
       argument to exec.  The syntax does not in any case work when used around  complex  commands  such  as
       parenthesised subshells or loops, where the opening brace is interpreted as part of a command list to
       be executed in the current shell.

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

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

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

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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

       will truncate all files in the current directory, assuming there's at least one.  (Without  the  MUL-TIOS MULTIOS
       TIOS 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 com-mand command
       mand  as shown can exit before file1 and file2 are completely written.  As a workaround, it is possi-ble possible
       ble 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  redirec-tions. redirections.
       tions.  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 redi-rections. redirections.
       rections.  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  READ-
       NULLCMD 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  begin-ning beginning
       ning  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 success-fully successfully
       fully handled the command, or non-zero status if it failed.  In the latter case the standard handling
       is applied: `command not found' is printed to standard error and the shell  exits  with  status  127.
       Note  that the handler is executed in a subshell forked to execute an external command, hence changes
       to directories, shell parameters, etc. have no effect on the main shell.

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

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

       The return builtin is used to return from function calls.

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

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

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

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

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

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

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

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

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

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

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

       Otherwise, the function body (with no surrounding `funcname() {...}') is taken  to  be  the  complete
       contents  of  the file.  This form allows the file to be used directly as an executable shell script.
       If processing of the file results in the function  being  re-defined,  the  function  itself  is  not
       re-executed.   To  force  the shell to perform initialization and then call the function defined, the
       file should contain initialization code (which will be executed then discarded) in addition to a com-plete complete
       plete  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 fol-lowing following
       lowing 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 func-tion function
       tion definition may be used: a `()' with no preceding name, or a `function' with an immediately  fol-lowing following
       lowing open brace.  The function is executed immediately at the point of definition and is not stored
       for future use.  The function name is set to `(anon)'.

       Arguments to the function may be specified as words following the closing brace  defining  the  func-tion, function,
       tion,  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 struc-ture structure
       ture enclosed in braces.  The main use of anonymous functions is to provide a scope for  local  vari-ables. variables.
       ables.   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 exe-cute; execute;
       cute; it is executed in the same context and with the same arguments  as  the  basic  function.   For
       example, if $chpwd_functions is an array containing the values `mychpwd', `chpwd_save_dirstack', then
       the shell attempts to execute the functions `chpwd', `mychpwd'  and  `chpwd_save_dirstack',  in  that
       order.   Any function that does not exist is silently ignored.  A function found by this mechanism is
       referred to elsewhere as a `hook function'.  An error in any function causes subsequent functions not
       to  be  run.   Note  further  that an error in a precmd hook causes an immediately following periodic
       function not to run (though it may run at the next opportunity).

       chpwd  Executed whenever the current working directory is changed.

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

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

       preexec
              Executed just after a command has been read and is about to be executed.  If the history mech-anism mechanism
              anism 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 com-mand command
              mand 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 func-tion function
              tion bodies elided); the third argument contains the full text that is being executed.

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

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

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

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

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

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


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

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

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

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

              Programs terminated by uncaught signals typically return the status 128 plus the  signal  num-ber. number.
              ber.   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 zsh-builtins(1) zshbuiltins(1)
              builtins(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  func-tion. function.
              tion.  The value of $? at the start of execution is the exit status of the shell or the return
              status of the function exiting.

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

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

              TRAPNAL() {
               # code
              }

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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

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

              [1] 1234

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

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

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

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

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

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

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

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

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

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

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

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

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

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

ARITHMETIC EVALUATION
       The shell can perform integer and floating point arithmetic, either using the builtin let, or  via  a
       substitution  of the form $((...)).  For integers, the shell is usually compiled to use 8-byte preci-sion precision
       sion 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.

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

       It is also possible to specify a base to be used for  output  in  the  form  `[#base]',  for  example
       `[#16]'.  This is used when outputting arithmetical substitutions or when assigning to scalar parame-ters, parameters,
       ters, 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 mathe-matical mathematical
       matical expression, the last encountered is used.  For clarity it is recommended that  it  appear  at
       the beginning of an expression.  As an example:

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

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

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

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

       Floating point constants are recognized by the presence of a decimal point or an exponent.  The deci-mal decimal
       mal point may be the first character of the constant, but the exponent character e or E may  not,  as
       it  will be taken for a parameter name.  All numeric parts (before and after the decimal point and in
       the exponent) may contain underscores after the leading digit for visual guidance; these are  ignored
       in computation.

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

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

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

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

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

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

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

              ((val2 = val1 * 2))

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

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

       Likewise, floating point numbers can be declared with the float builtin; there are two types, differ-ing differing
       ing 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 com-
       pare 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 reg-exp regexp
              exp is tested as a PCRE regular expression using the zsh/pcre module, else it is tested  as  a
              POSIX  extended  regular  expression  using the zsh/regex module.  Upon successful match, some
              variables will be updated; no variables are changed if the matching fails.

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

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

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

       Normal shell expansion is performed on the file, string and pattern arguments, but the result of each
       expansion  is constrained to be a single word, similar to the effect of double quotes.  Filename gen-eration generation
       eration 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,  com-mand command
       mand 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 num-ber. number.
       ber.  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  compo-nents components
              nents  of the hostname are desired.  With a negative integer, trailing components of the host-name hostname
              name are shown.

       %n     $USERNAME.

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


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

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

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

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

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

       %h
       %!     Current history event number.

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

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

       %j     The number of jobs.

       %L     The current value of $SHLVL.

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

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

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


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

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

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

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

       %w     The date in day-dd format.

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

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

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

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


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

       %E     Clear to end of line.

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

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

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

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

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

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

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

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

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


CONDITIONAL SUBSTRINGS IN PROMPTS
       %v     The value of the first element of the psvar array parameter.  Following the `%' with an  inte-ger integer
              ger 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 charac-ter character
              ter 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 arbitrarily-nested
              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 direc-tory, directory,
                     tory, 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, com-
              pletely replacing the truncated string.

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



zsh 5.0.2                                     December 21, 2012                                   ZSHMISC(1)

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