Provided by: zsh-common_5.4.2-3ubuntu3.2_all bug

NAME

       zshmisc - everything and then some

SIMPLE COMMANDS & PIPELINES

       A  simple command is a sequence of optional parameter assignments followed by blank-separated words, with
       optional redirections interspersed.  For a description of assignment, see the beginning of zshparam(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 pipeline is preceded by `!'
       in which case the value is the logical inverse of the value of the last command.  For example,

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

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

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

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

              dmesg | grep panic && print yes

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

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

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

PRECOMMAND MODIFIERS

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

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

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

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

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

              The -c option clears the environment.

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

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

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

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

COMPLEX COMMANDS

       A complex command in zsh is one of the following:

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

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

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

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

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

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

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

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

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

              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 terminator of the following list ;;, ;& or ;| is applied unless the
              esac is reached.

              If the list that is executed is terminated with ;|  the  shell  continues  to  scan  the  patterns
              looking  for  the  next  match,  executing  the  corresponding list, and applying the rule for the
              corresponding terminator ;;, ;& or ;|.  Note that word is not re-expanded; all applicable patterns
              are tested with the same word.

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

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

       { list }
              Execute list.

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

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

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

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

              Regardless of TRY_BLOCK_ERROR, after the end of always-list the normal  shell  status  $?  is  the
              value   returned  from  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 protecting code by executing it in a subshell.

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

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

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

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

              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 parameter.  If pipeline is omitted,  print  statistics  about  the  shell
              process and its children.

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

ALTERNATE FORMS FOR COMPLEX COMMANDS

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

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

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

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

              works, but

                     if true {  # Does not work!
                       print yes
                     }

              does not, since the test is not suitably delimited.

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

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

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

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

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

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

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

       repeat word sublist
              This is a short form of repeat.

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

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

       function word ... [ () ] [ term ] sublist
              This is a short form of function.

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 behaviour can be recovered by
       setting the option CONTINUE_ON_ERROR.

       Fatal errors found in non-interactive shells include:

       •      Failure to parse shell options passed when invoking the shell

       •      Failure to change options with the set builtin

       •      Parse errors of all sorts, including failures to parse mathematical expressions

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

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

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

       •      Disallowed operations when the RESTRICTED options is set

       •      Failure to create a pipe needed for a pipeline

       •      Failure to create a multio

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

       •      Errors creating command or process substitutions

       •      Syntax errors in glob qualifiers

       •      File generation errors where not caught by the option BAD_PATTERN

       •      All bad patterns used for matching within case statements

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

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

       •      Memory errors where detected by the shell

       •      Invalid subscripts to shell variables

       •      Attempts to assign read-only variables

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

       •      Use of invalid variable names

       •      Errors in variable substitution syntax

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

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

COMMENTS

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

ALIASING

       Every  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 purposes 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:

       •      Any plain string or glob pattern

       •      Any  quoted  string,  using  any  quoting  method  (note that the quotes must be part of the alias
              definition for this to be eligible)

       •      Any parameter reference or command substitution

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

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

       •      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  followed  by  a  character  that  isn't
       special,  it  may  be  more  convenient  to  quote  the  word by starting with a single quote, i.e. 'foo;
       completion will automatically add the trailing single quote.

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

              alias echobar='echo bar'; echobar

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

       Note also the unhelpful interaction of aliases and function definitions:

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

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

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

       which defines noglob as well as func as functions with the body given.  To avoid this, either  quote  the
       name func or use the alternative function definition form `function func'.  Ensuring the alias is defined
       after the function works but is problematic if the code fragment might be re-executed.

QUOTING

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

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

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

              print ''''

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

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

REDIRECTION

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

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

       < word Open file word for reading as standard input.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              ... 1>fname 2>&1

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

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

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

OPENING FILE DESCRIPTORS USING PARAMETERS

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

              ... {myfd}>&1

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

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

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

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

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

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

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

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

MULTIOS

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

              date >foo >bar

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

              date >foo | cat

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

       Note  also that redirections are always expanded in order.  This happens regardless of the setting of the
       MULTIOS option, but with the option in effect there are additional consequences. For example, the meaning
       of the expression >&1 will change after a previous redirection:

              date >&1 >output

       In  the case above, the >&1 refers to the standard output at the start of the line; the result is similar
       to the tee command.  However, consider:

              date >output >&1

       As redirections are evaluated in order, when the >&1 is encountered the standard output  is  set  to  the
       file  output  and another copy of the output is therefore sent to that file.  This is unlikely to be what
       is intended.

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

              : > *

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

              echo exit 0 >> *.sh

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

              sort <foo <fubar

       or even

              sort <f{oo,ubar}

       is equivalent to `cat foo fubar | sort'.

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

       Note that a pipe is an implicit redirection; thus

              cat bar | sort <foo

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

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

              echo 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 command with the given redirections.
       This is the default when emulating sh or ksh.

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

              < file

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

COMMAND EXECUTION

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

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

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

       If  no  external command is found but a function command_not_found_handler exists the shell executes this
       function with all command line arguments.  The return status of the function becomes the  status  of  the
       command.   If  the  function wishes to mimic the behaviour of the shell when the command is not found, it
       should print the message `command not found: cmd' to standard error and return status 127.  Note that the
       handler  is  executed  in a subshell forked to execute an external command, hence changes to directories,
       shell parameters, etc. have no effect on the main shell.

FUNCTIONS

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

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

       The return builtin is used to return from function calls.

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

AUTOLOADING FUNCTIONS

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

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

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

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

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

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

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

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

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

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

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

       For example, suppose the autoload file func contains

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

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

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

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

       and

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

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

              eval "$(functions)"

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

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

              autoload +X myfunc

ANONYMOUS FUNCTIONS

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

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

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

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

       For example,

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

       outputs the following:

              I am inside with arguments this and that
              I am outside

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

SPECIAL FUNCTIONS

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

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

       chpwd  Executed whenever the current working directory is changed.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

              TRAPNAL() {
               # code
              }

       ('function traps') and

              trap '
               # code
              ' NAL

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

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

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

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

JOBS

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

              [1] 1234

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

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

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

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

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

       One  additional  side  effect  is  that use of disown with a job created by suspending shell code in this
       fashion is delayed: the job can only be disowned once any process  started  from  the  parent  shell  has
       terminated.  At that point, the disowned job disappears silently from the job list.

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

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

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

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

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

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

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

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

SIGNALS

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

       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 corresponding precision is provided
       by the compiler and the library.

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

       For example, the following statement

              (( val = 2 + 1 ))

       is equivalent to

              let "val = 2 + 1"

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

       Integers can be in bases other than 10.  A leading `0x' or `0X' denotes hexadecimal 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 arithmetical substitutions or when assigning to scalar parameters, but an
       explicitly defined integer or floating point parameter will not be affected.  If an integer  variable  is
       implicitly  defined  by  an  arithmetic  expression,  any  base  specified in this way will be set as the
       variable's output arithmetic base as if the option `-i base' to the typeset builtin had been  used.   The
       expression  has  no  precedence  and  if  it occurs more than once in a mathematical expression, the last
       encountered is used.  For clarity it is recommended that it appear at the beginning of an expression.  As
       an example:

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

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

       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
       numbers will be treated similarly and hence appear as `077' instead of `8#77'.  This option has no effect
       on the output of bases other than hexadecimal and octal, and  these  formats  are  always  understood  on
       input.

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

       Floating  point  constants are recognized by the presence of a decimal point or an exponent.  The decimal
       point may be the first character of the constant, but the exponent character e or E may not, as  it  will
       be  taken  for  a  parameter  name.   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}crement
       << >>  bitwise shift left, right
       &      bitwise AND
       ^      bitwise XOR
       |      bitwise OR
       **     exponentiation
       * / %  multiplication, division, modulus (remainder)
       + -    addition, subtraction
       < > <= >=
              comparison
       == !=  equality and inequality
       &&     logical AND
       || ^^  logical OR, XOR
       ? :    ternary operator
       = += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
              assignment
       ,      comma operator

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

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

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

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

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

       An expression of the form `##x' where x is any character sequence such as `a', `^A', or  `\M-\C-x'  gives
       the  value of this character and an expression of the form `#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 character 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  specified  with  the  integer  builtin.
       Arithmetic  evaluation is performed on the value of each assignment to a named parameter declared integer
       in this manner.  Assigning a floating point number to an integer results in rounding 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 necessary.  In addition, if any operator
       which requires an integer (`&', `|', `^', `<<', `>>' and their equivalents with assignment)  is  given  a
       floating point argument, it will be silently rounded towards zero except for `~' which rounds down.

       Users  should  beware that, in common with many other programming languages 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
       expressions:

       -a file
              true if file exists.

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

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

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

       -e file
              true if file exists.

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

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

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

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

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

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

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

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

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

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

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

       -v varname
              true if shell variable varname is 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 two forms are  exactly  equivalent.   The  `='  form  is  the
              traditional shell syntax (and hence the only one generally used with the test and [ builtins); the
              `==' form provides compatibility with other sorts of computer language.

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

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

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

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

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

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

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

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

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

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

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

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

       ( exp )
              true if exp is true.

       ! exp  true if exp is false.

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

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

       For compatibility, if there is a single argument that  is  not  syntactically  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  recommended  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 single word, similar to the effect of double quotes.

       Filename generation is not performed on any form of argument to conditions.  However, it can be forced in
       any case where normal shell expansion 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 multiple 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 qualifier N ensures that the expression is empty if there is no matching
       file.

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

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

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

       For example, the following:

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

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

EXPANSION OF PROMPT SEQUENCES

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

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

       Certain escape sequences may be recognised in the prompt string.

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

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

SIMPLE PROMPT ESCAPES

   Special characters
       %%     A `%'.

       %)     A `)'.

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

       %M     The full machine hostname.

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

       %n     $USERNAME.

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

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

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

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

       %^     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
              integer 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 directories 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  integer
              may  follow  the  `%' to specify a number of trailing path components to show; zero means the full
              path.  A negative integer specifies leading components.

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

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

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

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

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

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

       %w     The date in day-dd format.

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

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

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

              In addition, if the system supports the  POSIX  gettimeofday  system  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 character causes a leading zero or space
              to be stripped is handled directly by the shell for the format characters d, f, H, k, l, m,  M,  S
              and  y;  any other format characters are provided to the system's strftime(3) with any leading `-'
              present, so the handling is system dependent.  Further GNU (or other) extensions are  also  passed
              to strftime(3) and may work if the system supports 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 position  of  the  %G  is  unimportant.
              Negative integers are not handled.

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

CONDITIONAL SUBSTRINGS IN PROMPTS

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

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

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

              !      True if the shell is running with privileges.
              #      True if the effective uid of the current process is n.
              ?      True if the exit status of the last command was n.
              _      True if at least n shell constructs were started.
              C
              /      True  if  the current absolute path has at least n elements relative to the root directory,
                     hence / is counted as 0 elements.
              c
              .
              ~      True if the current path, with prefix replacement, has at least n elements relative to  the
                     root directory, hence / is counted as 0 elements.
              D      True if the month is equal to n (January = 0).
              d      True if the day of the month is equal to n.
              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  displayed  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 immediately 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  character
              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 margin for RPROMPT).

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

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

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