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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 fol-
       lowed by  blank-separated  words,  with  optional  redirections  inter-
       spersed.   For  a  description of assignment, see the beginning of zsh-
       param(1).

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

              echo foo

       is a simple command with arguments.

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

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

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

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

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

              dmesg | grep panic && print yes

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

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

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


PRECOMMAND MODIFIERS

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

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

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

       command [ -pvV ]
              The command word is taken to be the name of an external command,
              rather than a shell function or builtin.   If the POSIX_BUILTINS
              option  is  set, builtins will also be executed but certain spe-
              cial 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 equiva-
              lent to whence -v.

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

              The -c option clears the environment.

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

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

       nocorrect
              Spelling  correction is not done on any of the words.  This must
              appear before any other precommand modifier,  as  it  is  inter-
              preted  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, exe-
              cuting list each time.  If the in word is omitted, use the posi-
              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 sec-
              tion `Arithmetic Evaluation').  The arithmetic expression  expr2
              is  repeatedly  evaluated  until  it  evaluates to zero and when
              non-zero, list is executed and the arithmetic  expression  expr3
              evaluated.   If any expression is omitted, then it behaves as if
              it evaluated to 1.

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

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

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

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

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

              Note further that, unless the SH_GLOB option is set,  the  whole
              pattern  with alternatives is treated by the shell as equivalent
              to a group of patterns within parentheses, although white  space
              may  appear  about the parentheses and the vertical bar and will
              be stripped from the pattern at those points.  White  space  may
              appear  elsewhere  in the pattern; this is not stripped.  If the
              SH_GLOB option is set, so that an  opening  parenthesis  can  be
              unambiguously treated as part of the case syntax, the expression
              is parsed into separate words and these are  treated  as  strict
              alternatives (as in other shells).

              If  the  list that is executed is terminated with ;& rather than
              ;;, the following list is also executed.  The rule for the  ter-
              minator 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, exe-
              cuting the corresponding list, and applying  the  rule  for  the
              corresponding  terminator  ;;,  ;& or ;|.  Note that word is not
              re-expanded; all applicable patterns are tested  with  the  same
              word.

       select name [ in word ... term ] do list done
              where  term  is one or more newline or ; to terminate the words.
              Print the set of words, each preceded by a number.   If  the  in
              word  is  omitted,  use  the positional parameters.  The PROMPT3
              prompt is printed and a line is read from the line editor if the
              shell is interactive and that is active, or else standard input.
              If this line consists of the number of one of the listed  words,
              then the parameter name is set to the word corresponding to this
              number.  If this line is empty, the selection  list  is  printed
              again.   Otherwise,  the  value  of the parameter name is set to
              null.  The contents of the line  read  from  standard  input  is
              saved  in the parameter REPLY.  list is executed for each selec-
              tion 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, con-
              tinue, or return commands encountered within  try-list,  execute
              always-list.   Execution  then  continues from the result of the
              execution of try-list; in other words, any error, or break, con-
              tinue,  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  func-
              tion,  script,  or  list.   Syntax  errors encountered while the
              shell is parsing the code do not cause  the  always-list  to  be
              executed.   For  example, an erroneously constructed if block in
              try-list would cause the shell to abort during parsing, so  that
              always-list  would not be executed, while an erroneous substitu-
              tion 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 use-
              ful (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  try-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 pro-
              tecting code by executing it in a subshell.

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

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

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

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

              In  any of the forms above, a redirection may appear outside the
              function body, for example

                     func() { ... } 2>&1

              The redirection is stored with the function and applied whenever
              the  function is executed.  Any variables in the redirection are
              expanded at the point the function is executed, but outside  the
              function scope.

       time [ pipeline ]
              The  pipeline is executed, and timing statistics are reported on
              the standard error in the form specified by the TIMEFMT  parame-
              ter.   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  com-
       mands, in both these cases the test part of the loop must also be suit-
       ably 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 ! [[ { } declare export float
       integer local readonly typeset

       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 functions or  shell
       constructs  such as loops or conditions; this somewhat illogical behav-
       iour can be recovered by setting the option CONTINUE_ON_ERROR.

       Fatal errors found in non-interactive shells include:

       o      Failure to parse shell options passed when invoking the shell

       o      Failure to change options with the set builtin

       o      Parse errors of all sorts, including failures to parse mathemat-
              ical expressions

       o      Failures  to  set  or  modify  variable  behaviour with typeset,
              local, declare, export, integer, float

       o      Execution of  incorrectly  positioned  loop  control  structures
              (continue, break)

       o      Attempts  to  use  regular expression with no regular expression
              module available

       o      Disallowed operations when the RESTRICTED options is set

       o      Failure to create a pipe needed for a pipeline

       o      Failure to create a multio

       o      Failure to autoload a module needed for a declared shell feature

       o      Errors creating command or process substitutions

       o      Syntax errors in glob qualifiers

       o      File  generation  errors where not caught by the option BAD_PAT-
              TERN

       o      All bad patterns used for matching within case statements

       o      File generation failures where not caused by NO_MATCH or similar
              options

       o      All  file generation errors where the pattern was used to create
              a multio

       o      Memory errors where detected by the shell

       o      Invalid subscripts to shell variables

       o      Attempts to assign read-only variables

       o      Logical errors with variables such as assignment  to  the  wrong
              type

       o      Use of invalid variable names

       o      Errors in variable substitution syntax

       o      Failure to convert characters in $'...' expressions

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



COMMENTS

       In  non-interactive  shells, or in interactive shells with the INTERAC-
       TIVE_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 eligible word 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 replacement text ends with
       a space, the next word in the shell input is always eligible  for  pur-
       poses of alias expansion.  An alias is defined using the alias builtin;
       global aliases may be defined using the -g option to that builtin.

       A word is defined as:

       o      Any plain string or glob pattern

       o      Any quoted string, using  any  quoting  method  (note  that  the
              quotes  must be part of the alias definition for this to be eli-
              gible)

       o      Any parameter reference or command substitution

       o      Any series of the foregoing, concatenated without whitespace  or
              other tokens between them

       o      Any reserved word (case, do, else, etc.)

       o      With  global  aliasing,  any  command separator, any redirection
              operator, and `(' or `)' when not part of a glob pattern

       It is not presently possible to alias the `(('  token  that  introduces
       arithmetic expressions, because until a full statement has been parsed,
       it cannot be distinguished from two consecutive `(' tokens  introducing
       nested subshells.

       When POSIX_ALIASES is set, only plain unquoted strings are eligible for
       aliasing.  The alias builtin does not reject  ineligible  aliases,  but
       they are not expanded.

       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.  Also, if a separator such as && is aliased, \&& turns  into  the
       two  tokens  \&  and &, each of which may have been aliased separately.
       Similarly for \<<, \>|, etc.

       For use with completion, which would remove an initial  backslash  fol-
       lowed  by  a character that isn't special, it may be more convenient to
       quote the word by starting with a single quote, i.e.  'foo;  completion
       will automatically add the trailing single quote.

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

              alias echobar='echo bar'; echobar

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

       Note also the unhelpful interaction of  aliases  and  function  defini-
       tions:

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

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

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

       which defines noglob as well as func as functions with the body  given.
       To  avoid this, either quote the name func or use the alternative func-
       tion 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  pre-
       ceding it with a `\'.  `\' followed by a newline is ignored.

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

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

              print ''''

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

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


REDIRECTION

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

       The following may appear anywhere in a simple command or may precede or
       follow a complex command.  Expansion occurs before  word  or  digit  is
       used except as noted below.  If the result of substitution on word pro-
       duces 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 CLOB-
              BER 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 substitu-
              tion 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.  Back-
              quotes in word do not have  their  usual  effect;  instead  they
              behave  similarly  to  double quotes, except that the backquotes
              themselves are passed through unchanged.  (This  information  is
              given for completeness and it is not recommended that backquotes
              be used.)  Quotes in the form $'...' have their standard  effect
              of expanding backslashed references to special characters.

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

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

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

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

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

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

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

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

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

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

              ... 1>fname 2>&1

       first associates file descriptor 1 with file fname.  It then associates
       file descriptor 2 with the file associated with file descriptor 1 (that
       is,  fname).  If the order of redirections were reversed, file descrip-
       tor 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  redirect-
       ion.   For  example,  if  word  in an output redirection is of the form
       `>(list)' then the output is piped to the command represented by  list.
       See Process Substitution in zshexpn(1).


OPENING FILE DESCRIPTORS USING PARAMETERS

       When  the shell is parsing arguments to a command, and the shell option
       IGNORE_BRACES is not set, a different form of redirection  is  allowed:
       instead  of  a digit before the operator there is a valid shell identi-
       fier 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  read-
       only.

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

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

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

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

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


MULTIOS

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

              date >foo >bar

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

              date >foo | cat

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

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

       Expansion of the redirection argument occurs at the point the redirect-
       ion  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 Hello > bar > baz

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

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

              cat file >file1 >file2
              cat file1 file2

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

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

              { cat file } >file >file2

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



REDIRECTIONS WITH NO COMMAND

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

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

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

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

              < file

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



COMMAND EXECUTION

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

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

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

       If no external command is found but a  function  command_not_found_han-
       dler  exists  the  shell  executes  this function with all command line
       arguments.  The function should return status zero if  it  successfully
       handled  the  command,  or non-zero status if it failed.  In the latter
       case the standard handling is applied: `command not found'  is  printed
       to  standard  error and the shell exits with status 127.  Note that the
       handler is executed in a subshell forked to execute  an  external  com-
       mand,  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 spe-
       cial  syntax  `funcname  ()'.   Shell  functions are read in and stored
       internally.  Alias names are resolved when the function is read.  Func-
       tions  are  executed  like  commands with the arguments passed as posi-
       tional 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 envi-
       ronment of the caller.

       The return builtin is used to return from function calls.

       Function  identifiers  can be listed with the functions builtin.  Func-
       tions 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 rec-
       ommended for the use of functions supplied with the  zsh  distribution.
       Note  that  for functions precompiled with the zcompile builtin command
       the flag -U must be provided when the .zwc file is created, as the cor-
       responding information is compiled into the latter.

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

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

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

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

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

       In  summary, the order of searching is, first, in the parents of direc-
       tories in fpath for the newer of  either  a  compiled  directory  or  a
       directory  in fpath; second, if more than one of these contains a defi-
       nition 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 execu-
       tion, 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 initializa-
       tion and then call the function defined, the file should  contain  ini-
       tialization code (which will be executed then discarded) in addition to
       a complete function definition (which will be retained  for  subsequent
       calls to the function), and a call to the shell function, including any
       arguments, at the end.

       For example, suppose the autoload file func contains

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

       then `func; func' with KSH_AUTOLOAD set will produce both  messages  on
       the  first  call, but only the message `This is func' on the second and
       subsequent calls.  Without KSH_AUTOLOAD set, it will produce  the  ini-
       tialization  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  follow-
       ing 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  iden-
       tified  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 execut-
       ing myfunc, use:

              autoload +X myfunc



ANONYMOUS FUNCTIONS

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

       Arguments to the function may be specified as words following the clos-
       ing  brace  defining the function, hence if there are none no arguments
       (other than $0) are set.  This is a difference from the way other func-
       tions  are  parsed: normal function definitions may be followed by cer-
       tain keywords such as `else' or `fi', which will be  treated  as  argu-
       ments  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  man-
       ner  as  to a current-shell structure enclosed in braces.  The main use
       of anonymous functions is to provide a scope for local variables.  This
       is  particularly  convenient  in start-up files as these do not provide
       their own local variable scope.

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

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



SPECIAL FUNCTIONS

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


   Hook Functions
       For the functions below, it is possible to define an array that has the
       same name as the function with `_functions' appended.  Any  element  in
       such an array is taken as the name of a function to execute; it is exe-
       cuted 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 immedi-
       ately following periodic function not to run (though it may run at  the
       next opportunity).

       chpwd  Executed whenever the current working directory is changed.

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

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

       preexec
              Executed  just  after a command has been read and is about to be
              executed.  If the history mechanism  is  active  (regardless  of
              whether  the  line  was  discarded from the history buffer), the
              string that the user typed is passed as the first argument, oth-
              erwise  it  is an empty string.  The actual command that will be
              executed (including expanded aliases) is passed in two different
              forms:  the  second argument is a single-line, size-limited ver-
              sion of the command (with things like function  bodies  elided);
              the  third  argument  contains  the full text that is being exe-
              cuted.

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

              If  any  of the hook functions returns status 1 (or any non-zero
              value other than 2, though this is  not  guaranteed  for  future
              versions  of  the  shell)  the  history  line will not be saved,
              although it lingers in the history until the next line  is  exe-
              cuted, allowing you to reuse or edit it immediately.

              If  any  of the hook functions returns status 2 the history line
              will be saved on the internal history list, but not  written  to
              the  history  file.   In  case of a conflict, the first non-zero
              status value is taken.

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

              The following example function works with  one  of  the  options
              INC_APPEND_HISTORY  or SHARE_HISTORY set, in order that the line
              is written out immediately after the history entry is added.  It
              first  adds the history line to the normal history with the new-
              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 nor-
              mally.   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 execu-
              tion continues normally.  Otherwise, the shell  will  behave  as
              interrupted  except  that  the  return  status  of  the  trap is
              retained.

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

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

              The  functions  TRAPZERR,  TRAPDEBUG and TRAPEXIT are never exe-
              cuted 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 com-
              mand.  See the description of the trap builtin in zshbuiltins(1)
              for details of additional features provided in debug traps.

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

       TRAPZERR
              Executed whenever a command has a non-zero  exit  status.   How-
              ever,  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 func-
              tion TRAPERR acts the same as TRAPZERR on systems where there is
              no SIGERR (this is the usual case).

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

              TRAPNAL() {
               # code
              }

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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


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 `sus-
       pended', and print another prompt.  You can then manipulate  the  state
       of  this  job, putting it in the background with the bg command, or run
       some other commands and then eventually bring the  job  back  into  the
       foreground  with  the foreground command fg.  A ^Z takes effect immedi-
       ately 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  con-
       tinue  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 func-
       tion was never suspended.  Zsh is different from many other  shells  in
       this regard.

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

       When  a  command  is  suspended and continued later with the fg or wait
       builtins, zsh restores tty modes that were in effect when it  was  sus-
       pended.   This (intentionally) does not apply if the command is contin-
       ued 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 nor-
       mally  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 notifi-
       cations 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 trig-
       gers 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  immedi-
       ately 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 com-
       mand  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').

       Certain jobs are run asynchronously  by  the  shell  other  than  those
       explicitly put into the background; even in cases where the shell would
       usually wait for such jobs, an explicit exit command or exit due to the
       option ERR_EXIT will cause the shell to exit without waiting.  Examples
       of such asynchronous jobs are process  substitution,  see  the  section
       PROCESS  SUBSTITUTION  in  the  zshexpn(1) manual page, and the handler
       processes for multios, see the section MULTIOS in the zshmisc(1) manual
       page.


ARITHMETIC EVALUATION

       The  shell  can  perform  integer and floating point arithmetic, either
       using the builtin let, or via a substitution of the form $((...)).  For
       integers,  the  shell is usually compiled to use 8-byte precision where
       this is available, otherwise precision is 4 bytes.  This can be tested,
       for example, by giving the command `print - $(( 12345678901 ))'; if the
       number appears unchanged, the precision is at least 8 bytes.   Floating
       point  arithmetic  always  uses  the `double' type with whatever corre-
       sponding 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 match-
       ing `))' 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 and a leading `0b' or `0B' binary.  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 arith-
       metical substitutions or when assigning to scalar  parameters,  but  an
       explicitly  defined  integer  or  floating  point parameter will not be
       affected.  If an integer variable is implicitly defined  by  an  arith-
       metic  expression,  any  base  specified in this way will be set as the
       variable's output arithmetic base as if the option  `-i  base'  to  the
       typeset builtin had been used.  The expression has no precedence and if
       it occurs more than once in a mathematical expression, the last encoun-
       tered  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 out-
       put base 16, while x (assuming it does not already exist) is implicitly
       typed  by  the arithmetic evaluation, where it acquires the output base
       8.

       The base may be replaced or followed by an underscore, which may itself
       be  followed  by  a  positive  integer (if it is missing the value 3 is
       used).  This indicates that underscores should  be  inserted  into  the
       output  string,  grouping the number for visual clarity.  The following
       integer specifies the number of digits to group together.  For example:

              setopt cbases
              print $(( [#16_4] 65536 ** 2 ))

       outputs `0x1_0000_0000'.

       The  feature can be used with floating point numbers, in which case the
       base must be omitted; grouping is away from  the  decimal  point.   For
       example,

              zmodload zsh/mathfunc
              print $(( [#_] sqrt(1e7) ))

       outputs  `3_162.277_660_168_379_5'  (the number of decimal places shown
       may vary).

       If the C_BASES option is set, hexadecimal numbers  are  output  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  num-
       bers  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  appro-
       priate  base prefix will be output if necessary, so that the value out-
       put is valid syntax for input.   If  the  #  is  doubled,  for  example
       `[##16]', then no base prefix is output.

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

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

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

       + - ! ~ ++ --
              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre-
              ment
       << >>  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  evalu-
       ated.  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 lan-
       guages that support the relevant operators:

       + - ! ~ ++ --
              unary plus/minus, logical NOT, complement, {pre,post}{in,de}cre-
              ment
       **     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 paren-
       theses 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/math-
       func may be loaded with the zmodload builtin to provide standard float-
       ing 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 `#name' gives the value of the  first  character
       of  the contents of the parameter name.  Character values are according
       to the character set used in the current locale; for multibyte  charac-
       ter  handling the option MULTIBYTE must be set.  Note that this form is
       different from `$#name', a standard parameter substitution which  gives
       the  length  of  the parameter name.  `#\' 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  speci-
       fied  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 towards zero.

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

       Promotion of integer to floating point values is performed where neces-
       sary.  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  towards  zero
       except for `~' which rounds down.

       Users  should  beware  that, in common with many other programming lan-
       guages but not software designed for calculation, the evaluation of  an
       expression  in  zsh is taken a term at a time and promotion of integers
       to floating point does not occur in terms only containing integers.   A
       typical  result of this is that a division such as 6/8 is truncated, in
       this being rounded towards 0.  The FORCE_FLOAT shell option can be used
       in  scripts  or  functions  where floating point evaluation is required
       throughout.

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

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

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

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


CONDITIONAL EXPRESSIONS

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

       -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 char-
              acter, in which case it is a single letter  option  name.   (See
              the section `Specifying Options'.)

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

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

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

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

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

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

       string =~ regexp
              true  if  string  matches the regular expression regexp.  If the
              option RE_MATCH_PCRE is set regexp is tested as a  PCRE  regular
              expression  using  the  zsh/pcre  module, else it is tested as a
              POSIX extended regular expression using  the  zsh/regex  module.
              Upon  successful match, some variables will be updated; no vari-
              ables 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  sub-
              strings 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 sub-
              strings 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 condi-
              tional 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.

       For compatibility, if there is a single argument that is not  syntacti-
       cally  significant, typically a variable, the condition is treated as a
       test for whether the expression expands as a string of non-zero length.
       In  other words, [[ $var ]] is the same as [[ -n $var ]].  It is recom-
       mended that the second, explicit, form be used where possible.

       Normal shell expansion is performed on the  file,  string  and  pattern
       arguments, but the result of each expansion is constrained to be a sin-
       gle word, similar to the effect of double quotes.

       Filename generation is not performed on any form of argument to  condi-
       tions.  However, it can be forced in any case where normal shell expan-
       sion is valid and when the option EXTENDED_GLOB is in effect  by  using
       an  explicit  glob qualifier of the form (#q) at the end of the string.
       A normal glob qualifier expression may appear between the `q'  and  the
       closing  parenthesis;  if  none  appears  the  expression has no effect
       beyond causing filename generation.  The results of filename generation
       are joined together to form a single word, as with the results of other
       forms of expansion.

       This special use of filename generation is only available with  the  [[
       syntax.   If the condition occurs within the [ or test builtin commands
       then globbing occurs instead as part of normal command  line  expansion
       before the condition is evaluated.  In this case it may generate multi-
       ple words which are likely to confuse the syntax of the test command.

       For example,

              [[ -n file*(#qN) ]]

       produces status zero if and only if there is at least one file  in  the
       current directory beginning with the string `file'.  The globbing qual-
       ifier N ensures that the expression is empty if there  is  no  matching
       file.

       Pattern  metacharacters  are active for the pattern arguments; the pat-
       terns are the same as those used  for  filename  generation,  see  zsh-
       expn(1), but there is no special behaviour of `/' nor initial dots, and
       no glob qualifiers are allowed.

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

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

       For example, the following:

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

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


EXPANSION OF PROMPT SEQUENCES

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

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

       Certain escape sequences may be recognised in the prompt string.

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

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



SIMPLE PROMPT ESCAPES

   Special characters
       %%     A `%'.

       %)     A `)'.


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

       %M     The full machine hostname.

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

       %n     $USERNAME.

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


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

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

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

       %^     The  status  of  the parser in reverse. This is the same as `%_'
              other than the order of strings.  It is often used in RPS2.

       %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  inte-
              ger  specifies leading components, i.e. %-1d specifies the first
              component.

       %~     As %d and %/, but if the current working directory  starts  with
              $HOME,  that part is replaced by a `~'. Furthermore, if it has a
              named directory as its prefix, that part is replaced  by  a  `~'
              followed by the name of the directory, but only if the result is
              shorter than the full path; see Dynamic and Static named  direc-
              tories in zshexpn(1).

       %e     Evaluation depth of the current sourced file, shell function, or
              eval.  This is incremented or decremented every time  the  value
              of  %N  is  set  or  reverted to a previous value, respectively.
              This is most useful for debugging as part of $PS4.

       %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 inte-
              ger may follow the `%' to specify a number of trailing path com-
              ponents  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 com-
              mand 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 depre-
              cated as %c and %C are equivalent to %1~ and %1/,  respectively,
              while explicit positive integers have the same effect as for the
              latter two sequences.


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

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

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

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

       %w     The date in day-dd format.

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

       %D{string}
              string is formatted using  the  strftime  function.   See  strf-
              time(3)  for  more details.  Various zsh extensions provide num-
              bers 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

              In  addition, if the system supports the POSIX gettimeofday sys-
              tem call, %. provides decimal fractions of a  second  since  the
              epoch  with leading zeroes.  By default three decimal places are
              provided, but a number of digits up to 6 may be given  following
              the  %;  hence  %6.  outputs microseconds.  A typical example of
              this is the format `%D{%H:%M:%S.%.}'.

              The GNU extension that a `-' between the % and the format  char-
              acter  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 the
              system's strftime(3) with any leading `-' present, so  the  han-
              dling  is  system  dependent.  Further GNU (or other) extensions
              are also passed to strftime(3) and may work if the  system  sup-
              ports them.


   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 posi-
              tion  of  the %G is unimportant.  Negative integers are not han-
              dled.

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



CONDITIONAL SUBSTRINGS IN PROMPTS

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

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

              The left parenthesis may be preceded or followed by  a  positive
              integer  n,  which defaults to zero.  A negative integer will be
              multiplied by -1, except as noted below for `l'.  The test char-
              acter x may be any of the following:

              !      True if the shell is running with privileges.
              #      True if the effective uid of the current process is n.
              ?      True if the exit status of the last command was n.
              _      True if at least n shell constructs were started.
              C
              /      True if the current absolute path has at least n elements
                     relative to the root directory, hence / is counted  as  0
                     elements.
              c
              .
              ~      True if the current path, with prefix replacement, has at
                     least n elements relative to the root directory, hence  /
                     is counted as 0 elements.
              D      True if the month is equal to n (January = 0).
              d      True if the day of the month is equal to n.
              e      True if the evaluation depth is at least 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.  When n  is  negative,  true  if  at
                     least abs(n) characters remain before the opposite margin
                     (thus the left margin for RPROMPT).
              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 string will be dis-
              played in place of the truncated portion  of  any  string;  note
              this does not undergo prompt expansion.

              The numeric argument, which in the third form may appear immedi-
              ately after the `[', specifies the maximum permitted  length  of
              the various strings that can be displayed in the prompt.  In the
              first two forms, this numeric argument may be negative, in which
              case  the  truncation  length  is  determined by subtracting the
              absolute value of the numeric argument from the number of  char-
              acter  positions  remaining on the current prompt line.  If this
              results in a zero or negative length, a length of 1 is used.  In
              other  words, a negative argument arranges that after truncation
              at least n characters remain before the right margin (left  mar-
              gin for RPROMPT).

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

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

              The part of the prompt string to be truncated runs to the end of
              the  string,  or  to  the end of the next enclosing group of the
              `%(' construct, or to the next  truncation  encountered  at  the
              same  grouping  level  (i.e. truncations inside a `%(' are sepa-
              rate), 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.
              Note  that `%-0<<' is not equivalent to `%<<' but specifies that
              the prompt is truncated at the right margin.

              Truncation applies only  within  each  individual  line  of  the
              prompt,  as  delimited  by  embedded  newlines (if any).  If the
              total length of any line  of  the  prompt  after  truncation  is
              greater  than the terminal width, or if the part to be truncated
              contains embedded newlines, truncation behavior is undefined and
              may   change   in   a   future   version   of  the  shell.   Use
              `%-n(l.true-text.false-text)' to remove parts of the prompt when
              the available space is less than n.



zsh 5.2                        December 2, 2015                     zshmisc(1)

Mac OS X 10.12.3 - Generated Sat Feb 4 15:33:16 CST 2017
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