Provided by: zsh-common_5.1.1-1ubuntu2.3_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.

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.

       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 function should return status zero if it successfully
       handled the command, or non-zero status if it failed.  In  the  latter  case  the  standard  handling  is
       applied: `command not found' is printed to standard error and the shell exits with status 127.  Note that
       the handler is executed  in  a  subshell  forked  to  execute  an  external  command,  hence  changes  to
       directories, shell parameters, etc. have no effect on the main shell.

FUNCTIONS

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

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

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

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

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

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

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

SIGNALS

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

       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 down to the next
       integer.

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

       Promotion of integer to floating point values is performed where necessary.  In addition, if any operator
       which requires an integer (`~', `&', `|', `^', `%', `<<', `>>' and their equivalents with assignment)  is
       given a floating point argument, it will be silently rounded down to the next integer.

       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 down to 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.

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

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

       -z string
              true if length of string is zero.

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

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

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

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

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

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

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

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

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

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

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

              If the option BASH_REMATCH is not set the scalar parameter MATCH is  set  to  the  substring  that
              matched  the pattern and the integer parameters MBEGIN and MEND to the index of the start and end,
              respectively, of the match in string, such that  if  string  is  contained  in  variable  var  the
              expression `${var[$MBEGIN,$MEND]}' is identical to `$MATCH'.  The setting of the option KSH_ARRAYS
              is respected.  Likewise, the array match is set  to  the  substrings  that  matched  parenthesised
              subexpressions  and  the  arrays  mbegin  and  mend to the indices of the start and end positions,
              respectively, of the substrings  within  string.   The  arrays  are  not  set  if  there  were  no
              parenthesised 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.