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       zshexpn - zsh expansion and substitution


       The following types of expansions are performed in the indicated order in five steps:

       History Expansion
              This is performed only in interactive shells.

       Alias Expansion
              Aliases  are  expanded  immediately  before the command line is parsed as explained
              under Aliasing in zshmisc(1).

       Process Substitution
       Parameter Expansion
       Command Substitution
       Arithmetic Expansion
       Brace Expansion
              These five are performed in left-to-right fashion.  On each argument,  any  of  the
              five  steps that are needed are performed one after the other.  Hence, for example,
              all the parts of parameter expansion are completed before command  substitution  is
              started.   After  these  expansions,  all  unquoted  occurrences  of the characters
              `\',`'' and `"' are removed.

       Filename Expansion
              If the SH_FILE_EXPANSION option is set, the order  of  expansion  is  modified  for
              compatibility  with  sh  and  ksh.   In  that  case filename expansion is performed
              immediately after alias expansion, preceding the set of five  expansions  mentioned

       Filename Generation
              This expansion, commonly referred to as globbing, is always done last.

       The following sections explain the types of expansion in detail.


       History  expansion allows you to use words from previous command lines in the command line
       you are typing.  This simplifies spelling corrections and the  repetition  of  complicated
       commands or arguments.

       Immediately before execution, each command is saved in the history list, the size of which
       is controlled by the HISTSIZE parameter.  The one most recent command is  always  retained
       in  any  case.   Each  saved  command in the history list is called a history event and is
       assigned a number, beginning with 1 (one) when the shell starts up.   The  history  number
       that  you  may see in your prompt (see EXPANSION OF PROMPT SEQUENCES in zshmisc(1)) is the
       number that is to be assigned to the next command.

       A history expansion begins with the first character of the histchars parameter,  which  is
       `!' by default, and may occur anywhere on the command line, including inside double quotes
       (but not inside single quotes '...' or C-style quotes  $'...'  nor  when  escaped  with  a

       The  first  character  is followed by an optional event designator (see the section `Event
       Designators') and then an optional word designator (the section  `Word  Designators');  if
       neither of these designators is present, no history expansion occurs.

       Input  lines containing history expansions are echoed after being expanded, but before any
       other expansions take place and before the command is executed.  It is this expanded  form
       that is recorded as the history event for later references.

       History expansions do not nest.

       By  default,  a history reference with no event designator refers to the same event as any
       preceding history reference on that command line; if it is the only history reference in a
       command,  it refers to the previous command.  However, if the option CSH_JUNKIE_HISTORY is
       set, then every history reference  with  no  event  specification  always  refers  to  the
       previous command.

       For example, `!' is the event designator for the previous command, so `!!:1' always refers
       to the first word of the previous command, and `!!$' always refers to the last word of the
       previous  command.   With CSH_JUNKIE_HISTORY set, then `!:1' and `!$' function in the same
       manner as `!!:1' and `!!$', respectively.  Conversely,  if  CSH_JUNKIE_HISTORY  is  unset,
       then  `!:1'  and  `!$'  refer to the first and last words, respectively, of the same event
       referenced by the nearest other history reference preceding them on  the  current  command
       line, or to the previous command if there is no preceding reference.

       The  character  sequence  `^foo^bar'  (where  `^'  is actually the second character of the
       histchars parameter) repeats the last command, replacing the string foo  with  bar.   More
       precisely,  the  sequence  `^foo^bar^'  is  synonymous  with  `!!:s^foo^bar^', hence other
       modifiers (see the  section  `Modifiers')  may  follow  the  final  `^'.   In  particular,
       `^foo^bar^:G' performs a global substitution.

       If the shell encounters the character sequence `!"' in the input, the history mechanism is
       temporarily disabled until the current list (see zshmisc(1)) is fully parsed.  The `!"' is
       removed from the input, and any subsequent `!' characters have no special significance.

       A  less  convenient but more comprehensible form of command history support is provided by
       the fc builtin.

   Event Designators
       An event designator is a reference to a command-line entry in the history  list.   In  the
       list below, remember that the initial `!' in each item may be changed to another character
       by setting the histchars parameter.

       !      Start a history expansion, except when followed by a blank, newline,  `='  or  `('.
              If  followed immediately by a word designator (see the section `Word Designators'),
              this  forms  a  history  reference  with  no  event  designator  (see  the  section

       !!     Refer  to  the  previous  command.   By itself, this expansion repeats the previous

       !n     Refer to command-line n.

       !-n    Refer to the current command-line minus n.

       !str   Refer to the most recent command starting with str.

              Refer to the most recent command containing str.  The trailing `?' is necessary  if
              this  reference is to be followed by a modifier or followed by any text that is not
              to be considered part of str.

       !#     Refer to the current command line typed in so far.  The line is treated  as  if  it
              were complete up to and including the word before the one with the `!#' reference.

       !{...} Insulate a history reference from adjacent characters (if necessary).

   Word Designators
       A word designator indicates which word or words of a given command line are to be included
       in a history reference.  A `:' usually separates the event  specification  from  the  word
       designator.   It  may  be omitted only if the word designator begins with a `^', `$', `*',
       `-' or `%'.  Word designators include:

       0      The first input word (command).
       n      The nth argument.
       ^      The first argument.  That is, 1.
       $      The last argument.
       %      The word matched by (the most recent) ?str search.
       x-y    A range of words; x defaults to 0.
       *      All the arguments, or a null value if there are none.
       x*     Abbreviates `x-$'.
       x-     Like `x*' but omitting word $.

       Note that a `%' word designator works only when used in one of `!%', `!:%' or  `!?str?:%',
       and  only  when used after a !? expansion (possibly in an earlier command).  Anything else
       results in an error, although the error may not be the most obvious one.

       After the optional word designator, you can add a sequence of one or more of the following
       modifiers,  each  preceded  by a `:'.  These modifiers also work on the result of filename
       generation and parameter expansion, except where noted.

       a      Turn a file name into  an  absolute  path:   prepends  the  current  directory,  if
              necessary; remove `.' path segments; and remove `..' path segments and the segments
              that immediately precede them.

              This transformation is agnostic about what is in the filesystem,  i.e.  is  on  the
              logical,  not  the  physical  directory.  It takes place in the same manner as when
              changing directories when neither of the options CHASE_DOTS or CHASE_LINKS is  set.
              For  example,  `/before/here/../after'  is  always  transformed to `/before/after',
              regardless of whether `/before/here' exists or what  kind  of  object  (dir,  file,
              symlink, etc.) it is.

       A      Turn  a file name into an absolute path as the `a' modifier does, and then pass the
              result through the realpath(3) library function to resolve symbolic links.

              Note: on systems that do not have a realpath(3) library  function,  symbolic  links
              are not resolved, so on those systems `a' and `A' are equivalent.

              Note:  foo:A  and  realpath(foo)  are  different on some inputs.  For realpath(foo)
              semantics, see the `P` modifier.

       c      Resolve a command name into an absolute path by searching the command path given by
              the  PATH  variable.   This  does not work for commands containing directory parts.
              Note also that this does not usually work as a glob qualifier unless a file of  the
              same name is found in the current directory.

       e      Remove  all  but  the  part  of  the  filename extension following the `.'; see the
              definition of the filename extension in the description of the  r  modifier  below.
              Note  that according to that definition the result will be empty if the string ends
              with a `.'.

       h      Remove a trailing pathname component, leaving the head.  This works like `dirname'.

       l      Convert the words to all lowercase.

       p      Print the new command but do not execute it.  Only works with history expansion.

       P      Turn a file name into an absolute path, like realpath(3).  The resulting path  will
              be  absolute, have neither `.' nor `..' components, and refer to the same directory
              entry as the input filename.

              Unlike realpath(3), non-existent trailing components are permitted and preserved.

       q      Quote the substituted words, escaping further substitutions.   Works  with  history
              expansion  and  parameter expansion, though for parameters it is only useful if the
              resulting text is to be re-evaluated such as by eval.

       Q      Remove one level of quotes from the substituted words.

       r      Remove a filename extension leaving  the  root  name.   Strings  with  no  filename
              extension are not altered.  A filename extension is a `.' followed by any number of
              characters (including zero) that are neither `.' nor `/' and that continue  to  the
              end  of  the  string.   For  example,  the  extension  of `foo.orig.c' is `.c', and
              `dir.c/foo' has no extension.

              Substitute r for l as described below.  The substitution is done only for the first
              string  that  matches  l.   For arrays and for filename generation, this applies to
              each word of the expanded text.  See below for further notes on substitutions.

              The forms `gs/l/r' and `s/l/r/:G'  perform  global  substitution,  i.e.  substitute
              every  occurrence  of  r  for  l.  Note that the g or :G must appear in exactly the
              position shown.

              See further notes on this form of substitution below.

       &      Repeat the previous s substitution.  Like s, may be preceded immediately  by  a  g.
              In  parameter expansion the & must appear inside braces, and in filename generation
              it must be quoted with a backslash.

       t      Remove all  leading  pathname  components,  leaving  the  tail.   This  works  like

       u      Convert the words to all uppercase.

       x      Like  q,  but  break  into  words  at  whitespace.   Does  not  work with parameter

       The s/l/r/ substitution works as follows.  By default the left-hand side of  substitutions
       are  not  patterns,  but character strings.  Any character can be used as the delimiter in
       place of `/'.  A backslash quotes the delimiter character.   The  character  `&',  in  the
       right-hand-side  r,  is  replaced  by  the text from the left-hand-side l.  The `&' can be
       quoted with a backslash.  A null l uses the previous string either from the previous l  or
       from  the  contextual scan string s from `!?s'.  You can omit the rightmost delimiter if a
       newline immediately follows r; the rightmost `?'  in  a  context  scan  can  similarly  be
       omitted.   Note  the  same  record  of  the last l and r is maintained across all forms of

       Note that if a `&' is used within glob qualifiers an extra backslash is needed as a & is a
       special character in this case.

       Also  note  that the order of expansions affects the interpretation of l and r.  When used
       in a history expansion, which occurs before any other expansions, l and r are  treated  as
       literal  strings  (except  as  explained  for  HIST_SUBST_PATTERN  below).   When  used in
       parameter expansion, the replacement of r into the parameter's value is  done  first,  and
       then  any  additional  process,  parameter,  command,  arithmetic, or brace references are
       applied, which may evaluate those substitutions and expansions more than once if l appears
       more than once in the starting value.  When used in a glob qualifier, any substitutions or
       expansions are performed once at the time the qualifier is parsed, even  before  the  `:s'
       expression itself is divided into l and r sides.

       If  the  option  HIST_SUBST_PATTERN  is  set,  l is treated as a pattern of the usual form
       described in the section FILENAME GENERATION below.  This can be used in  all  the  places
       where  modifiers  are  available;  note,  however,  that  in globbing qualifiers parameter
       substitution has already taken place, so parameters in the replacement  string  should  be
       quoted  to  ensure  they  are  replaced  at  the correct time.  Note also that complicated
       patterns used in globbing  qualifiers  may  need  the  extended  glob  qualifier  notation
       (#q:s/.../.../)  in  order  for the shell to recognize the expression as a glob qualifier.
       Further, note that bad patterns in the substitution are not subject to the  NO_BAD_PATTERN
       option so will cause an error.

       When  HIST_SUBST_PATTERN  is  set,  l may start with a # to indicate that the pattern must
       match at the start of the string to be substituted, and a % may appear  at  the  start  or
       after  an  #  to  indicate  that  the  pattern  must  match at the end of the string to be
       substituted.  The % or # may be quoted with two backslashes.

       For example, the following piece  of  filename  generation  code  with  the  EXTENDED_GLOB

              print *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/)

       takes  the  expansion  of  *.c  and applies the glob qualifiers in the (#q...) expression,
       which consists of a substitution modifier anchored to the start and end of each word (#%).
       This  turns on backreferences ((#b)), so that the parenthesised subexpression is available
       in the replacement string as ${match[1]}.  The replacement string is quoted  so  that  the
       parameter is not substituted before the start of filename generation.

       The  following  f,  F,  w  and W modifiers work only with parameter expansion and filename
       generation.  They are listed  here  to  provide  a  single  point  of  reference  for  all

       f      Repeats  the  immediately  (without a colon) following modifier until the resulting
              word doesn't change any more.

              Like f, but repeats only n times if  the  expression  expr  evaluates  to  n.   Any
              character  can  be  used  instead  of  the  `:'; if `(', `[', or `{' is used as the
              opening delimiter, the closing delimiter should be ')', `]', or `}', respectively.

       w      Makes the immediately following modifier work on each word in the string.

       W:sep: Like w but words are considered to be the parts of the string that are separated by
              sep.  Any character can be used instead of the `:'; opening parentheses are handled
              specially, see above.


       Each part of a command argument that takes the form `<(list)', `>(list)' or  `=(list)'  is
       subject  to  process  substitution.   The  expression may be preceded or followed by other
       strings except that, to prevent clashes with commonly occurring strings and patterns,  the
       last  form  must occur at the start of a command argument, and the forms are only expanded
       when first parsing command or assignment arguments.  Process  substitutions  may  be  used
       following  redirection  operators;  in  this  case,  the  substitution must appear with no
       trailing string.

       Note that `<<(list)' is not a special syntax; it is equivalent to `< <(list)', redirecting
       standard  input  from  the  result  of  process  substitution.   Hence  all  the following
       documentation applies.  The second form (with the space) is recommended for clarity.

       In the case of the < or > forms, the shell runs the commands in list as  a  subprocess  of
       the  job  executing the shell command line.  If the system supports the /dev/fd mechanism,
       the command argument is the name of the device file corresponding to  a  file  descriptor;
       otherwise,  if  the  system  supports  named pipes (FIFOs), the command argument will be a
       named pipe.  If the form with > is selected then writing on this special file will provide
       input  for  list.   If < is used, then the file passed as an argument will be connected to
       the output of the list process.  For example,

              paste <(cut -f1 file1) <(cut -f3 file2) |
              tee >(process1) >(process2) >/dev/null

       cuts fields 1 and 3 from the files  file1  and  file2  respectively,  pastes  the  results
       together, and sends it to the processes process1 and process2.

       If  =(...) is used instead of <(...), then the file passed as an argument will be the name
       of a temporary file containing the output of the list process.  This may be  used  instead
       of the < form for a program that expects to lseek (see lseek(2)) on the input file.

       There  is  an  optimisation  for  substitutions  of  the  form  =(<<<arg),  where arg is a
       single-word argument to the here-string redirection <<<.  This form produces a  file  name
       containing  the value of arg after any substitutions have been performed.  This is handled
       entirely within the current shell.  This is effectively the reverse of  the  special  form
       $(<arg) which treats arg as a file name and replaces it with the file's contents.

       The  = form is useful as both the /dev/fd and the named pipe implementation of <(...) have
       drawbacks.  In  the  former  case,  some  programmes  may  automatically  close  the  file
       descriptor in question before examining the file on the command line, particularly if this
       is necessary for security reasons such as when the programme is running  setuid.   In  the
       second  case, if the programme does not actually open the file, the subshell attempting to
       read from or write to the pipe will (in  a  typical  implementation,  different  operating
       systems may have different behaviour) block for ever and have to be killed explicitly.  In
       both cases, the shell actually supplies the information using a pipe, so  that  programmes
       that expect to lseek (see lseek(2)) on the file will not work.

       Also  note  that  the  previous  example  can  be  more  compactly and efficiently written
       (provided the MULTIOS option is set) as:

              paste <(cut -f1 file1) <(cut -f3 file2) \
              > >(process1) > >(process2)

       The shell uses pipes instead of FIFOs to implement the latter two process substitutions in
       the above example.

       There  is  an  additional  problem  with  >(process); when this is attached to an external
       command, the parent shell does not wait for process to finish  and  hence  an  immediately
       following command cannot rely on the results being complete.  The problem and solution are
       the same as described in the section MULTIOS in zshmisc(1).  Hence in a simplified version
       of the example above:

              paste <(cut -f1 file1) <(cut -f3 file2) > >(process)

       (note  that  no  MULTIOS  are  involved), process will be run asynchronously as far as the
       parent shell is concerned.  The workaround is:

              { paste <(cut -f1 file1) <(cut -f3 file2) } > >(process)

       The extra processes here are spawned from the parent  shell  which  will  wait  for  their

       Another  problem  arises any time a job with a substitution that requires a temporary file
       is disowned by the shell, including the case where `&!' or `&|' appears at the  end  of  a
       command containing a substitution.  In that case the temporary file will not be cleaned up
       as the shell no longer has any memory of the job.  A workaround is to use a subshell,  for

              (mycmd =(myoutput)) &!

       as the forked subshell will wait for the command to finish then remove the temporary file.

       A general workaround to ensure a process substitution endures for an appropriate length of
       time is to pass it as a parameter to an anonymous shell function (a piece  of  shell  code
       that is run immediately with function scope).  For example, this code:

              () {
                 print File $1:
                 cat $1
              } =(print This be the verse)

       outputs something resembling the following

              File /tmp/zsh6nU0kS:
              This be the verse

       The  temporary  file created by the process substitution will be deleted when the function


       The character `$' is used to  introduce  parameter  expansions.   See  zshparam(1)  for  a
       description of parameters, including arrays, associative arrays, and subscript notation to
       access individual array elements.

       Note in particular the fact that words of unquoted parameters are not automatically  split
       on  whitespace unless the option SH_WORD_SPLIT is set; see references to this option below
       for more details.  This is an important difference from other shells.

       In the expansions discussed below that require a pattern, the form of the pattern  is  the
       same  as  that  used for filename generation; see the section `Filename Generation'.  Note
       that these patterns, along with the replacement text of any substitutions, are  themselves
       subject  to  parameter  expansion,  command  substitution,  and  arithmetic expansion.  In
       addition to the following  operations,  the  colon  modifiers  described  in  the  section
       `Modifiers'   in   the   section   `History  Expansion'  can  be  applied:   for  example,
       ${i:s/foo/bar/} performs string substitution on the expansion of parameter $i.

       In the following descriptions, `word' refers to a single word substituted on  the  command
       line,   not  necessarily  a  space  delimited  word.   With  default  options,  after  the

              array=("first word" "second word")
              scalar="only word"

       then $array substitutes two words, `first word' and `second word', and $scalar substitutes
       a  single  word `only word'.  This may be modified by explicit or implicit word-splitting,
       however.  The full rules are complicated and are noted at the end.

              The value, if any, of the parameter name is substituted.  The braces  are  required
              if the expansion is to be followed by a letter, digit, or underscore that is not to
              be  interpreted  as  part  of  name.   In  addition,  more  complicated  forms   of
              substitution usually require the braces to be present; exceptions, which only apply
              if the option KSH_ARRAYS is not set, are a single subscript or any colon  modifiers
              appearing  after  the  name,  or  any  of  the characters `^', `=', `~', `#' or `+'
              appearing before the name, all of which work with or without braces.

              If name is an array parameter, and the KSH_ARRAYS option is not set, then the value
              of  each  element  of  name  is  substituted, one element per word.  Otherwise, the
              expansion results in one word only; with KSH_ARRAYS, this is the first  element  of
              an array.  No field splitting is done on the result unless the SH_WORD_SPLIT option
              is set.  See also the flags = and s:string:.

              If name is the name of a  set  parameter  `1'  is  substituted,  otherwise  `0'  is

              If  name  is  set,  or  in  the second form is non-null, then substitute its value;
              otherwise substitute word.  In the second form name may be omitted, in  which  case
              word is always substituted.

              If  name is set, or in the second form is non-null, then substitute word; otherwise
              substitute nothing.

              In the first form, if name is unset then set it to word; in  the  second  form,  if
              name  is  unset or null then set it to word; and in the third form, unconditionally
              set name to word.  In all forms, the value of the parameter is then substituted.

              In the first form, if name is set, or in the second form if name is  both  set  and
              non-null, then substitute its value; otherwise, print word and exit from the shell.
              Interactive shells instead return to the  prompt.   If  word  is  omitted,  then  a
              standard message is printed.

       In  any  of  the  above expressions that test a variable and substitute an alternate word,
       note that you can use standard shell quoting in the word value to selectively override the
       splitting  done  by  the  SH_WORD_SPLIT  option  and  the = flag, but not splitting by the
       s:string: flag.

       In the following expressions, when name is an array and the substitution is not quoted, or
       if  the `(@)' flag or the name[@] syntax is used, matching and replacement is performed on
       each array element separately.

              If the pattern matches the beginning of the value  of  name,  then  substitute  the
              value  of  name  with  the  matched portion deleted; otherwise, just substitute the
              value of name.  In the first form, the smallest matching pattern is  preferred;  in
              the second form, the largest matching pattern is preferred.

              If  the  pattern matches the end of the value of name, then substitute the value of
              name with the matched portion deleted; otherwise,  just  substitute  the  value  of
              name.  In the first form, the smallest matching pattern is preferred; in the second
              form, the largest matching pattern is preferred.

              If the pattern matches the  value  of  name,  then  substitute  the  empty  string;
              otherwise,  just  substitute  the  value of name.  If name is an array the matching
              array elements are removed (use the `(M)' flag to remove the non-matched elements).

              If arrayname is the name (N.B., not  contents)  of  an  array  variable,  then  any
              elements  contained in arrayname are removed from the substitution of name.  If the
              substitution is scalar, either because name is a scalar variable or the  expression
              is  quoted,  the  elements  of  arrayname  are  instead  tested  against the entire

              Similar to the preceding substitution, but in the opposite sense, so  that  entries
              present in both the original substitution and as elements of arrayname are retained
              and others removed.

              Zips two arrays, such that the output array  is  twice  as  long  as  the  shortest
              (longest  for  `:^^')  of name and arrayname, with the elements alternatingly being
              picked from them. For `:^', if one of the input arrays is longer, the  output  will
              stop when the end of the shorter array is reached.  Thus,

                     a=(1 2 3 4); b=(a b); print ${a:^b}

              will  output  `1  a  2  b'.  For `:^^', then the input is repeated until all of the
              longer array has been used up and the above will output `1 a 2 b 3 a 4 b'.

              Either or both inputs may be a scalar, they will be treated as an array of length 1
              with  the  scalar as the only element. If either array is empty, the other array is
              output with no extra elements inserted.

              Currently the following code will output `a b' and `1' as  two  separate  elements,
              which  can  be  unexpected.  The  second  print  provides a workaround which should
              continue to work if this is changed.

                     a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}"

              This  syntax  gives  effects  similar  to  parameter  subscripting  in   the   form
              $name[start,end],  but  is  compatible with other shells; note that both offset and
              length are interpreted differently from the components of a subscript.

              If offset is non-negative, then if the variable name is  a  scalar  substitute  the
              contents  starting offset characters from the first character of the string, and if
              name is an array substitute  elements  starting  offset  elements  from  the  first
              element.   If  length  is  given,  substitute  that  many  characters  or elements,
              otherwise the entire rest of the scalar or array.

              A positive offset is always treated as the offset of a character or element in name
              from the first character or element of the array (this is different from native zsh
              subscript notation).  Hence 0 refers to the first character or  element  regardless
              of the setting of the option KSH_ARRAYS.

              A  negative offset counts backwards from the end of the scalar or array, so that -1
              corresponds to the last character or element, and so on.

              When positive, length counts from the offset position toward the end of the  scalar
              or  array.   When  negative, length counts back from the end.  If this results in a
              position smaller than offset, a diagnostic is printed and nothing is substituted.

              The option MULTIBYTE  is  obeyed,  i.e.  the  offset  and  length  count  multibyte
              characters where appropriate.

              offset  and  length  undergo  the  same  set  of  shell substitutions as for scalar
              assignment; in addition, they are then subject to  arithmetic  evaluation.   Hence,
              for example

                     print ${foo:3}
                     print ${foo: 1 + 2}
                     print ${foo:$(( 1 + 2))}
                     print ${foo:$(echo 1 + 2)}

              all have the same effect, extracting the string starting at the fourth character of
              $foo if the substitution would otherwise return a scalar, or the array starting  at
              the  fourth  element  if  $foo  would  return  an array.  Note that with the option
              KSH_ARRAYS $foo always returns a scalar  (regardless  of  the  use  of  the  offset
              syntax)  and a form such as ${foo[*]:3} is required to extract elements of an array
              named foo.

              If offset is negative, the - may  not  appear  immediately  after  the  :  as  this
              indicates the ${name:-word} form of substitution.  Instead, a space may be inserted
              before the -.  Furthermore, neither offset nor length may begin with an  alphabetic
              character  or  &  as  these  are  used  to  indicate  history-style  modifiers.  To
              substitute a value from a variable, the recommended approach is to precede it  with
              a  $ as this signifies the intention (parameter substitution can easily be rendered
              unreadable); however, as  arithmetic  substitution  is  performed,  the  expression
              ${var: offs} does work, retrieving the offset from $offs.

              For  further  compatibility  with  other  shells  there is a special case for array
              offset 0.  This usually accesses the first element of the array.  However,  if  the
              substitution refers to the positional parameter array, e.g. $@ or $*, then offset 0
              instead refers to $0, offset 1 refers to $1,  and  so  on.   In  other  words,  the
              positional  parameter  array  is  effectively  extended  by  prepending  $0.  Hence
              ${*:0:1} substitutes $0 and ${*:1:1} substitutes $1.

              Replace the longest possible match of pattern in the expansion of parameter name by
              string  repl.   The  first form replaces just the first occurrence, the second form
              all occurrences, and the third form replaces only if  pattern  matches  the  entire
              string.   Both  pattern and repl are subject to double-quoted substitution, so that
              expressions like ${name/$opat/$npat} will  work,  but  obey  the  usual  rule  that
              pattern  characters  in  $opat  are  not treated specially unless either the option
              GLOB_SUBST is set, or $opat is instead substituted as ${~opat}.

              The pattern may begin with a `#', in which case the pattern must match at the start
              of  the  string,  or  `%', in which case it must match at the end of the string, or
              `#%' in which case the pattern must match the entire string.  The repl  may  be  an
              empty  string, in which case the final `/' may also be omitted.  To quote the final
              `/' in other cases it should be  preceded  by  a  single  backslash;  this  is  not
              necessary  if  the  `/'  occurs inside a substituted parameter.  Note also that the
              `#', `%' and `#% are not active if they occur inside a substituted parameter,  even
              at the start.

              If, after quoting rules apply, ${name} expands to an array, the replacements act on
              each element individually.  Note also the effect of the I and S parameter expansion
              flags below; however, the flags M, R, B, E and N are not useful.

              For example,

                     foo="twinkle twinkle little star" sub="t*e" rep="spy"
                     print ${foo//${~sub}/$rep}
                     print ${(S)foo//${~sub}/$rep}

              Here,  the  `~' ensures that the text of $sub is treated as a pattern rather than a
              plain string.  In the first case, the longest match for t*e is substituted and  the
              result  is `spy star', while in the second case, the shortest matches are taken and
              the result is `spy spy lispy star'.

              If spec is one of the above substitutions, substitute the length in  characters  of
              the  result  instead  of  the  result  itself.   If  spec  is  an array expression,
              substitute the number of elements of the result.  This  has  the  side-effect  that
              joining  is skipped even in quoted forms, which may affect other sub-expressions in
              spec.  Note that `^', `=', and `~', below, must appear to  the  left  of  `#'  when
              these forms are combined.

              If  the  option  POSIX_IDENTIFIERS  is not set, and spec is a simple name, then the
              braces are optional; this is true even for special parameters so e.g. $#-  and  $#*
              take   the   length   of   the  string  $-  and  the  array  $*  respectively.   If
              POSIX_IDENTIFIERS is set, then braces are required for the # to be treated in  this

              Turn  on  the  RC_EXPAND_PARAM  option  for  the  evaluation of spec; if the `^' is
              doubled, turn it off.  When this option  is  set,  array  expansions  of  the  form
              foo${xx}bar,  where  the  parameter  xx  is  set  to  (a b c), are substituted with
              `fooabar foobbar foocbar' instead of the default `fooa b cbar'.  Note that an empty
              array will therefore cause all arguments to be removed.

              Internally,  each  such  expansion  is converted into the equivalent list for brace
              expansion.  E.g.,  ${^var}  becomes  {$var[1],$var[2],...},  and  is  processed  as
              described  in  the  section  `Brace  Expansion' below: note, however, the expansion
              happens immediately, with any explicit brace expansion happening  later.   If  word
              splitting is also in effect the $var[N] may themselves be split into different list

              Perform word splitting using the rules for SH_WORD_SPLIT during the  evaluation  of
              spec,  but regardless of whether the parameter appears in double quotes; if the `='
              is doubled, turn it off.   This  forces  parameter  expansions  to  be  split  into
              separate  words  before  substitution,  using  IFS as a delimiter.  This is done by
              default in most other shells.

              Note that splitting is applied to word in the assignment forms of spec  before  the
              assignment to name is performed.  This affects the result of array assignments with
              the A flag.

              Turn on the GLOB_SUBST option for the evaluation of spec; if the  `~'  is  doubled,
              turn it off.  When this option is set, the string resulting from the expansion will
              be interpreted as a  pattern  anywhere  that  is  possible,  such  as  in  filename
              expansion and filename generation and pattern-matching contexts like the right hand
              side of the `=' and `!=' operators in conditions.

              In nested substitutions, note that the effect of the ~ applies to the result of the
              current  level  of substitution.  A surrounding pattern operation on the result may
              cancel it.  Hence, for example, if the parameter foo is set to  *,  ${~foo//\*/*.c}
              is  substituted  by  the pattern *.c, which may be expanded by filename generation,
              but ${${~foo}//\*/*.c} substitutes to the string *.c, which  will  not  be  further

       If  a  ${...}  type  parameter expression or a $(...) type command substitution is used in
       place of name above, it is expanded first and the result is used as if it were  the  value
       of  name.   Thus  it  is  possible  to  perform  nested  operations:   ${${foo#head}%tail}
       substitutes the value of $foo with both `head' and `tail' deleted.  The form  with  $(...)
       is  often  useful  in  combination  with the flags described next; see the examples below.
       Each name or nested ${...} in a parameter expansion may also be followed  by  a  subscript
       expression as described in Array Parameters in zshparam(1).

       Note  that double quotes may appear around nested expressions, in which case only the part
       inside is treated as quoted; for example, ${(f)"$(foo)"} quotes the result of $(foo),  but
       the  flag  `(f)'  (see  below)  is  applied using the rules for unquoted expansions.  Note
       further  that  quotes  are  themselves  nested  in   this   context;   for   example,   in
       "${(@f)"$(foo)"}", there are two sets of quotes, one surrounding the whole expression, the
       other (redundant) surrounding the $(foo) as before.

   Parameter Expansion Flags
       If the opening brace is directly followed by an opening parenthesis, the string up to  the
       matching closing parenthesis will be taken as a list of flags.  In cases where repeating a
       flag is meaningful, the repetitions need not be consecutive; for example, `(q%q%q)'  means
       the same thing as the more readable `(%%qqq)'.  The following flags are supported:

       #      Evaluate  the  resulting  words  as  numeric  expressions and output the characters
              corresponding to the resulting integer.  Note that this form is  entirely  distinct
              from use of the # without parentheses.

              If  the  MULTIBYTE  option  is  set and the number is greater than 127 (i.e. not an
              ASCII character) it is treated as a Unicode character.

       %      Expand all % escapes in the resulting words in the same  way  as  in  prompts  (see
              EXPANSION  OF  PROMPT  SEQUENCES  in zshmisc(1)). If this flag is given twice, full
              prompt expansion is done on the resulting words, depending on the  setting  of  the

       @      In  double quotes, array elements are put into separate words.  E.g., `"${(@)foo}"'
              is equivalent to `"${foo[@]}"' and `"${(@)foo[1,2]}"' is  the  same  as  `"$foo[1]"
              "$foo[2]"'.   This  is  distinct from field splitting by the f, s or z flags, which
              still applies within each array element.

       A      Convert the substitution into an array expression, even if it  otherwise  would  be
              scalar.   This  has  lower  precedence  than  subscripting,  so one level of nested
              expansion is required in order that  subscripts  apply  to  array  elements.   Thus
              ${${(A)name}[1]} yields the full value of name when name is scalar.

              This assigns an array parameter with `${...=...}', `${...:=...}' or `${...::=...}'.
              If this flag is repeated (as in `AA'),  assigns  an  associative  array  parameter.
              Assignment  is  made  before  sorting or padding; if field splitting is active, the
              word part is split before assignment.  The name part may be a subscripted range for
              ordinary  arrays;  when  assigning  an  associative  array,  the  word part must be
              converted to an array, for example by using `${(AA)=name=...}'  to  activate  field

              Surrounding  context  such  as  additional  nesting or use of the value in a scalar
              assignment may cause the array to be joined back into a single string again.

       a      Sort in array index order; when combined with  `O'  sort  in  reverse  array  index
              order.  Note that `a' is therefore equivalent to the default but `Oa' is useful for
              obtaining an array's elements in reverse order.

       b      Quote with backslashes only characters that are special to pattern  matching.  This
              is  useful  when  the  contents  of the variable are to be tested using GLOB_SUBST,
              including the ${~...} switch.

              Quoting using one of the q family of flags does not work  for  this  purpose  since
              quotes are not stripped from non-pattern characters by GLOB_SUBST.  In other words,

                     [[ $str = ${~pattern} ]]

              works if $str is `a*b' but not if it is `a b', whereas

                     [[ $str = ${~pattern} ]]

              is always true for any possible value of $str.

       c      With ${#name}, count the total number of characters in an array, as if the elements
              were concatenated with spaces between them.  This is not a true join of the  array,
              so  other expressions used with this flag may have an effect on the elements of the
              array before it is counted.

       C      Capitalize the resulting words.  `Words'  in  this  case  refers  to  sequences  of
              alphanumeric  characters  separated  by non-alphanumerics, not to words that result
              from field splitting.

       D      Assume the string or array elements contain directories and attempt  to  substitute
              the  leading part of these by names.  The remainder of the path (the whole of it if
              the leading part was not substituted) is then quoted so that the whole  string  can
              be  used  as  a  shell argument.  This is the reverse of `~' substitution:  see the
              section FILENAME EXPANSION below.

       e      Perform  single  word  shell  expansions,  namely  parameter   expansion,   command
              substitution and arithmetic expansion, on the result. Such expansions can be nested
              but too deep recursion may have unpredictable effects.

       f      Split the result of the expansion at newlines. This is a shorthand for `ps:\n:'.

       F      Join the words of arrays  together  using  newline  as  a  separator.   This  is  a
              shorthand for `pj:\n:'.

              Process  escape  sequences  like  the echo builtin when no options are given (g::).
              With the o option, octal escapes don't take a leading zero.   With  the  c  option,
              sequences  like  `^X'  are also processed.  With the e option, processes `\M-t' and
              similar sequences like the print builtin.  With  both  of  the  o  and  e  options,
              behaves  like  the  print  builtin  except  that  in  none  of  these modes is `\c'

       i      Sort case-insensitively.  May be combined with `n' or `O'.

       k      If name refers to an associative array, substitute the keys (element names)  rather
              than the values of the elements.  Used with subscripts (including ordinary arrays),
              force indices or keys to be substituted  even  if  the  subscript  form  refers  to
              values.   However,  this  flag may not be combined with subscript ranges.  With the
              KSH_ARRAYS option a subscript `[*]' or `[@]' is needed  to  operate  on  the  whole
              array, as usual.

       L      Convert all letters in the result to lower case.

       n      Sort  decimal  integers  numerically; if the first differing characters of two test
              strings are not digits, sorting is lexical.   Integers with more initial zeroes are
              sorted  before  those  with  fewer  or none.  Hence the array `foo1 foo02 foo2 foo3
              foo20 foo23' is sorted into the order shown.  May be combined with `i' or `O'.

       o      Sort the resulting words in ascending order; if this appears on its own the sorting
              is  lexical  and  case-sensitive  (unless  the locale renders it case-insensitive).
              Sorting in ascending order is the default for other forms of sorting,  so  this  is
              ignored if combined with `a', `i' or `n'.

       O      Sort  the resulting words in descending order; `O' without `a', `i' or `n' sorts in
              reverse lexical order.  May be combined with `a', `i' or `n' to reverse  the  order
              of sorting.

       P      This  forces  the  value  of  the  parameter  name  to  be interpreted as a further
              parameter name, whose value will be used where appropriate.  Note  that  flags  set
              with one of the typeset family of commands (in particular case transformations) are
              not applied to the value of name used in this fashion.

              If used with a nested parameter or command substitution, the result of that will be
              taken  as a parameter name in the same way.  For example, if you have `foo=bar' and
              `bar=baz', the strings ${(P)foo},  ${(P)${foo}},  and  ${(P)$(echo  bar)}  will  be
              expanded to `baz'.

              Likewise,  if  the  reference  is  itself  nested,  the expression with the flag is
              treated as if it were directly replaced by the parameter name.  It is an  error  if
              this  nested  substitution produces an array with more than one word.  For example,
              if  `name=assoc'  where  the  parameter  assoc  is  an  associative   array,   then
              `${${(P)name}[elt]}' refers to the element of the associative subscripted `elt'.

       q      Quote  characters  that  are  special  to  the  shell  in  the resulting words with
              backslashes; unprintable or invalid characters are quoted using the  $'\NNN'  form,
              with separate quotes for each octet.

              If this flag is given twice, the resulting words are quoted in single quotes and if
              it is given three times, the words are quoted in double quotes; in these  forms  no
              special handling of unprintable or invalid characters is attempted.  If the flag is
              given four times, the words are quoted in single quotes preceded by a $.  Note that
              in  all three of these forms quoting is done unconditionally, even if this does not
              change the way the resulting string would be interpreted by the shell.

              If a q- is given (only a single q may appear), a minimal form of single quoting  is
              used  that  only  quotes  the  string  if  needed  to  protect  special characters.
              Typically this form gives the most readable output.

              If a q+ is  given,  an  extended  form  of  minmal  quoting  is  used  that  causes
              unprintable  characters  to  be  rendered using $'...'.  This quoting is similar to
              that used by the output of values by the typeset family of commands.

       Q      Remove one level of quotes from the resulting words.

       t      Use a string describing the type of the parameter where the value of the  parameter
              would  usually appear. This string consists of keywords separated by hyphens (`-').
              The first keyword in the string describes the main type, it can be one of `scalar',
              `array',  `integer', `float' or `association'. The other keywords describe the type
              in more detail:

              local  for local parameters

              left   for left justified parameters

                     for right justified parameters with leading blanks

                     for right justified parameters with leading zeros

              lower  for parameters whose value is  converted  to  all  lower  case  when  it  is

              upper  for  parameters  whose  value  is  converted  to  all  upper case when it is

                     for readonly parameters

              tag    for tagged parameters

              export for exported parameters

              unique for arrays which keep only the first occurrence of duplicated values

              hide   for parameters with the `hide' flag

                     for parameters with the `hideval' flag

                     for special parameters defined by the shell

       u      Expand only the first occurrence of each unique word.

       U      Convert all letters in the result to upper case.

       v      Used with k, substitute (as two consecutive words) both the key and  the  value  of
              each  associative  array  element.   Used  with  subscripts,  force  values  to  be
              substituted even if the subscript form refers to indices or keys.

       V      Make any special characters in the resulting words visible.

       w      With ${#name}, count words in arrays or strings; the s flag may be used  to  set  a
              word delimiter.

       W      Similar  to  w with the difference that empty words between repeated delimiters are
              also counted.

       X      With this flag, parsing errors occurring with the Q, e and # flags or  the  pattern
              matching  forms  such  as `${name#pattern}' are reported.  Without the flag, errors
              are silently ignored.

       z      Split the result of the expansion into words using shell parsing to find the words,
              i.e.  taking  into  account  any  quoting  in  the value.  Comments are not treated
              specially  but  as  ordinary  strings,  similar  to  interactive  shells  with  the
              INTERACTIVE_COMMENTS  option  unset  (however,  see  the  Z  flag below for related

              Note that this is done very late, even later than the  `(s)'  flag.  So  to  access
              single words in the result use nested expansions as in `${${(z)foo}[2]}'. Likewise,
              to remove the quotes in the resulting words use `${(Q)${(z)foo}}'.

       0      Split the result of the expansion on null bytes.  This is a shorthand for `ps:\0:'.

       The following flags (except p) are followed by  one  or  more  arguments  as  shown.   Any
       character,  or  the  matching  pairs `(...)', `{...}', `[...]', or `<...>', may be used in
       place of a colon as delimiters, but note that when a flag takes more than one argument,  a
       matched pair of delimiters must surround each argument.

       p      Recognize the same escape sequences as the print builtin in string arguments to any
              of the flags described below that follow this argument.

              Alternatively, with this option string arguments may be in the form $var  in  which
              case  the  value  of  the  variable  is substituted.  Note this form is strict; the
              string argument does not undergo general parameter expansion.

              For example,

                     print ${(ps.$sep.)val}

              splits the variable on a :.

       ~      Strings inserted into the expansion by any of the flags below are to be treated  as
              patterns.   This  applies to the string arguments of flags that follow ~ within the
              same set of parentheses.  Compare with ~  outside  parentheses,  which  forces  the
              entire substituted string to be treated as a pattern.  Hence, for example,

                     [[ "?" = ${(~j.|.)array} ]]

              treats  `|' as a pattern and succeeds if and only if $array contains the string `?'
              as an element.  The ~ may be repeated to toggle  the  behaviour;  its  effect  only
              lasts to the end of the parenthesised group.

              Join  the  words  of  arrays  together using string as a separator.  Note that this
              occurs before field splitting by the s:string: flag or the SH_WORD_SPLIT option.

              Pad the resulting words on the left.  Each word will be truncated if  required  and
              placed in a field expr characters wide.

              The arguments :string1: and :string2: are optional; neither, the first, or both may
              be given.  Note that the same pairs of delimiters must be  used  for  each  of  the
              three  arguments.   The space to the left will be filled with string1 (concatenated
              as often as needed) or spaces if string1 is not given.  If both string1 and string2
              are given, string2 is inserted once directly to the left of each word, truncated if
              necessary, before string1 is used to produce any remaining padding.

              If either of string1 or string2 is present but empty, i.e. there are two delimiters
              together at that point, the first character of $IFS is used instead.

              If  the  MULTIBYTE option is in effect, the flag m may also be given, in which case
              widths will be used for the calculation of padding; otherwise individual  multibyte
              characters are treated as occupying one unit of width.

              If  the  MULTIBYTE  option  is not in effect, each byte in the string is treated as
              occupying one unit of width.

              Control characters are always  assumed  to  be  one  unit  wide;  this  allows  the
              mechanism to be used for generating repetitions of control characters.

       m      Only  useful  together  with  one of the flags l or r or with the # length operator
              when the MULTIBYTE option is in effect.  Use the character width  reported  by  the
              system  in  calculating how much of the string it occupies or the overall length of
              the string.  Most printable characters have a width of one  unit,  however  certain
              Asian  character  sets  and certain special effects use wider characters; combining
              characters have zero width.  Non-printable characters are  arbitrarily  counted  as
              zero width; how they would actually be displayed will vary.

              If the m is repeated, the character either counts zero (if it has zero width), else
              one.  For printable character strings this has the effect of counting the number of
              glyphs   (visibly  separate  characters),  except  for  the  case  where  combining
              characters themselves have non-zero width (true in certain alphabets).

              As l, but pad the words on the right and insert string2 immediately to the right of
              the string to be padded.

              Left and right padding may be used together.  In this case the strategy is to apply
              left padding to the first half width of each of  the  resulting  words,  and  right
              padding  to  the  second  half.  If the string to be padded has odd width the extra
              padding is applied on the left.

              Force field splitting at the separator string.  Note that a string of two  or  more
              characters  means  that  all  of them must match in sequence; this differs from the
              treatment of two or more characters in the IFS parameter.  See also the = flag  and
              the  SH_WORD_SPLIT  option.   An empty string may also be given in which case every
              character will be a separate element.

              For historical reasons, the usual behaviour that empty array elements are  retained
              inside  double  quotes  is  disabled  for  arrays generated by splitting; hence the

                     print -l "${(s.:.)line}"

              produces two lines of output for one and three and  elides  the  empty  field.   To
              override this behaviour, supply the `(@)' flag as well, i.e.  "${(@s.:.)line}".

              As  z  but  takes  a  combination  of  option  letters  between a following pair of
              delimiter characters.  With no options the effect is identical to z.  (Z+c+) causes
              comments  to  be  parsed as a string and retained; any field in the resulting array
              beginning with an unquoted comment character is a comment.  (Z+C+) causes  comments
              to  be  parsed  and removed.  The rule for comments is standard: anything between a
              word starting with the third character of $HISTCHARS, default #,  up  to  the  next
              newline  is  a  comment.  (Z+n+) causes unquoted newlines to be treated as ordinary
              whitespace, else they are  treated  as  if  they  are  shell  code  delimiters  and
              converted  to  semicolons.  Options are combined within the same set of delimiters,
              e.g. (Z+Cn+).

              The underscore (_) flag is reserved for future use.  As of this  revision  of  zsh,
              there  are  no  valid  flags; anything following an underscore, other than an empty
              pair of delimiters, is treated as an error, and the flag itself has no effect.

       The following flags are meaningful with the ${...#...} or ${...%...} forms.  The S  and  I
       flags may also be used with the ${.../...} forms.

       S      Search  substrings  as  well as beginnings or ends; with # start from the beginning
              and with % start from the end of the string.  With substitution via  ${.../...}  or
              ${...//...},  specifies  non-greedy matching, i.e. that the shortest instead of the
              longest match should be replaced.

              Search the exprth match (where expr evaluates to a number).  This only applies when
              searching  for  substrings,  either  with  the S flag, or with ${.../...} (only the
              exprth match is substituted) or ${...//...} (all matches from  the  exprth  on  are
              substituted).  The default is to take the first match.

              The exprth match is counted such that there is either one or zero matches from each
              starting  position  in  the  string,  although  for  global  substitution   matches
              overlapping previous replacements are ignored.  With the ${...%...} and ${...%%...}
              forms, the starting position for the match moves backwards  from  the  end  as  the
              index increases, while with the other forms it moves forward from the start.

              Hence with the string
                     which switch is the right switch for Ipswich?
              substitutions  of  the  form ${(SI:N:)string#w*ch} as N increases from 1 will match
              and remove `which', `witch', `witch' and `wich'; the form using `##' will match and
              remove  `which  switch is the right switch for Ipswich', `witch is the right switch
              for Ipswich', `witch for Ipswich' and `wich'. The form using `%'  will  remove  the
              same  matches as for `#', but in reverse order, and the form using `%%' will remove
              the same matches as for `##' in reverse order.

       B      Include the index of the beginning of the match in the result.

       E      Include the index one character past the end of the match in the result (note  this
              is inconsistent with other uses of parameter index).

       M      Include the matched portion in the result.

       N      Include the length of the match in the result.

       R      Include the unmatched portion in the result (the Rest).

       Here  is  a  summary  of  the rules for substitution; this assumes that braces are present
       around the substitution, i.e. ${...}.  Some particular examples  are  given  below.   Note
       that  the  Zsh  Development Group accepts no responsibility for any brain damage which may
       occur during the reading of the following rules.

       1. Nested substitution
              If multiple nested ${...} forms are present, substitution  is  performed  from  the
              inside  outwards.   At  each  level,  the substitution takes account of whether the
              current value is a scalar or an array, whether the whole substitution is in  double
              quotes,  and  what flags are supplied to the current level of substitution, just as
              if the nested substitution were the outermost.  The flags are not propagated up  to
              enclosing  substitutions; the nested substitution will return either a scalar or an
              array as determined by the flags, possibly adjusted for quoting.  All the following
              steps take place where applicable at all levels of substitution.

              Note  that,  unless  the  `(P)' flag is present, the flags and any subscripts apply
              directly to the value of  the  nested  substitution;  for  example,  the  expansion
              ${${foo}}  behaves exactly the same as ${foo}.  When the `(P)' flag is present in a
              nested substitution, the other substitution rules are applied to the  value  before
              it is interpreted as a name, so ${${(P)foo}} may differ from ${(P)foo}.

              At  each  nested  level of substitution, the substituted words undergo all forms of
              single-word  substitution  (i.e.  not  filename  generation),   including   command
              substitution,  arithmetic  expansion and filename expansion (i.e. leading ~ and =).
              Thus, for example, ${${:-=cat}:h} expands to the directory where  the  cat  program
              resides.   (Explanation:  the  internal substitution has no parameter but a default
              value =cat, which is expanded by filename expansion  to  a  full  path;  the  outer
              substitution  then  applies  the  modifier  :h  and takes the directory part of the

       2. Internal parameter flags
              Any parameter flags set by one of the typeset family of commands, in particular the
              -L,  -R, -Z, -u and -l options for padding and capitalization, are applied directly
              to the parameter value.  Note these flags are options to the command, e.g. `typeset
              -Z'; they are not the same as the flags used within parameter substitutions.

              At  the  outermost  level  of substitution, the `(P)' flag (rule 4.)  ignores these
              transformations and uses the unmodified value of the parameter as the  name  to  be
              replaced.   This is usually the desired behavior because padding may make the value
              syntactically illegal as a  parameter  name,  but  if  capitalization  changes  are
              desired, use the ${${(P)foo}} form (rule 25.).

       3. Parameter subscripting
              If  the value is a raw parameter reference with a subscript, such as ${var[3]}, the
              effect of subscripting is  applied  directly  to  the  parameter.   Subscripts  are
              evaluated  left  to right; subsequent subscripts apply to the scalar or array value
              yielded by the previous subscript.  Thus if var is an array,  ${var[1][2]}  is  the
              second  character  of  the  first word, but ${var[2,4][2]} is the entire third word
              (the second word of the range of words two through four  of  the  original  array).
              Any number of subscripts may appear.  Flags such as `(k)' and `(v)' which alter the
              result of subscripting are applied.

       4. Parameter name replacement
              At the outermost level of nesting only, the `(P)' flag is applied.  This treats the
              value  so  far  as  a parameter name (which may include a subscript expression) and
              replaces that with the corresponding value.  This replacement occurs later  if  the
              `(P)' flag appears in a nested substitution.

              If  the  value  so  far  names a parameter that has internal flags (rule 2.), those
              internal flags are applied to the new value after replacement.

       5. Double-quoted joining
              If the value after this process is an array, and the substitution appears in double
              quotes,  and  neither  an  `(@)'  flag  nor a `#' length operator is present at the
              current level, then words of the value are joined with the first character  of  the
              parameter  $IFS,  by default a space, between each word (single word arrays are not
              modified).  If the `(j)' flag is present, that is used for joining instead of $IFS.

       6. Nested subscripting
              Any remaining subscripts (i.e. of a nested  substitution)  are  evaluated  at  this
              point,  based  on  whether the value is an array or a scalar.  As with 3., multiple
              subscripts  can  appear.   Note  that  ${foo[2,4][2]}   is   thus   equivalent   to
              ${${foo[2,4]}[2]}  and  also  to  "${${(@)foo[2,4]}[2]}"  (the  nested substitution
              returns an array in  both  cases),  but  not  to  "${${foo[2,4]}[2]}"  (the  nested
              substitution returns a scalar because of the quotes).

       7. Modifiers
              Any  modifiers, as specified by a trailing `#', `%', `/' (possibly doubled) or by a
              set of modifiers of the form `:...' (see the section  `Modifiers'  in  the  section
              `History Expansion'), are applied to the words of the value at this level.

       8. Character evaluation
              Any `(#)' flag is applied, evaluating the result so far numerically as a character.

       9. Length
              Any  initial `#' modifier, i.e. in the form ${#var}, is used to evaluate the length
              of the expression so far.

       10. Forced joining
              If the `(j)' flag is present, or no `(j)' flag is present but the string is  to  be
              split as given by rule 11., and joining did not take place at rule 5., any words in
              the value are joined together using the given string or the first character of $IFS
              if none.  Note that the `(F)' flag implicitly supplies a string for joining in this

       11. Simple word splitting
              If one of the `(s)' or `(f)' flags are present, or the `='  specifier  was  present
              (e.g. ${=var}), the word is split on occurrences of the specified string, or (for =
              with neither of the two flags present) any of the characters in $IFS.

              If no `(s)', `(f)' or `=' was given, but the word is  not  quoted  and  the  option
              SH_WORD_SPLIT  is set, the word is split on occurrences of any of the characters in
              $IFS.  Note this step, too, takes place at all levels of a nested substitution.

       12. Case modification
              Any case modification from one of the flags `(L)', `(U)' or `(C)' is applied.

       13. Escape sequence replacement
              First any replacements from the `(g)' flag are  performed,  then  any  prompt-style
              formatting from the `(%)' family of flags is applied.

       14. Quote application
              Any quoting or unquoting using `(q)' and `(Q)' and related flags is applied.

       15. Directory naming
              Any directory name substitution using `(D)' flag is applied.

       16. Visibility enhancement
              Any modifications to make characters visible using the `(V)' flag are applied.

       17. Lexical word splitting
              If  the  '(z)'  flag  or one of the forms of the '(Z)' flag is present, the word is
              split as if it were a shell  command  line,  so  that  quotation  marks  and  other
              metacharacters  are  used  to  decide  what  constitutes a word.  Note this form of
              splitting is entirely distinct from that described by rule 11.:  it  does  not  use
              $IFS, and does not cause forced joining.

       18. Uniqueness
              If  the  result  is an array and the `(u)' flag was present, duplicate elements are
              removed from the array.

       19. Ordering
              If the result is still an array and one of the `(o)' or `(O)'  flags  was  present,
              the array is reordered.

       20. RC_EXPAND_PARAM
              At  this  point the decision is made whether any resulting array elements are to be
              combined element  by  element  with  surrounding  text,  as  given  by  either  the
              RC_EXPAND_PARAM option or the `^' flag.

       21. Re-evaluation
              Any  `(e)'  flag  is  applied  to  the  value, forcing it to be re-examined for new
              parameter substitutions, but also for command and arithmetic substitutions.

       22. Padding
              Any padding of the value by the `(l.fill.)' or `(r.fill.)' flags is applied.

       23. Semantic joining
              In contexts where expansion semantics requires a single word to result,  all  words
              are  rejoined  with  the first character of IFS between.  So in `${(P)${(f)lines}}'
              the value of ${lines} is split at newlines, but then must be  joined  again  before
              the `(P)' flag can be applied.

              If a single word is not required, this rule is skipped.

       24. Empty argument removal
              If  the  substitution  does  not appear in double quotes, any resulting zero-length
              argument, whether from a scalar or an element of an array, is elided from the  list
              of arguments inserted into the command line.

              Strictly  speaking,  the removal happens later as the same happens with other forms
              of substitution; the point to note here is simply that it occurs after any  of  the
              above parameter operations.

       25. Nested parameter name replacement
              If  the  `(P)'  flag  is  present  and rule 4. has not applied, the value so far is
              treated as a parameter name (which may include a subscript expression) and replaced
              with  the  corresponding  value,  with  internal flags (rule 2.) applied to the new

       The flag f is useful to split a double-quoted substitution line  by  line.   For  example,
       ${(f)"$(<file)"}  substitutes the contents of file divided so that each line is an element
       of the resulting array.  Compare this with the effect of $(<file) alone, which divides the
       file  up by words, or the same inside double quotes, which makes the entire content of the
       file a single string.

       The following illustrates the rules for nested parameter expansions.   Suppose  that  $foo
       contains the array (bar baz):

              This  produces  the result b.  First, the inner substitution "${foo}", which has no
              array (@) flag, produces a single word result "bar baz".   The  outer  substitution
              "${(@)...[1]}"  detects that this is a scalar, so that (despite the `(@)' flag) the
              subscript picks the first character.

              This produces the result `bar'.  In this case, the inner  substitution  "${(@)foo}"
              produces  the  array  `(bar baz)'.  The outer substitution "${...[1]}" detects that
              this is an array and picks the first word.  This is  similar  to  the  simple  case

       As an example of the rules for word splitting and joining, suppose $foo contains the array
       `(ax1 bx1)'.  Then

              produces the words `a', `1 b' and `1'.

              produces `a', `1', `b' and `1'.

              produces `a' and ` b' (note the extra space).  As substitution occurs before either
              joining  or  splitting,  the operation  first generates the modified array (ax bx),
              which is joined to give "ax bx", and then split to give `a',  `  b'  and  `'.   The
              final empty string will then be elided, as it is not in double quotes.


       A command enclosed in parentheses preceded by a dollar sign, like `$(...)', or quoted with
       grave accents, like ``...`', is replaced with  its  standard  output,  with  any  trailing
       newlines  deleted.   If  the  substitution is not enclosed in double quotes, the output is
       broken into words using the IFS parameter.

       The substitution `$(cat foo)' may be replaced by the faster `$(<foo)'.  In this  case  foo
       undergoes  single  word  shell  expansions  (parameter expansion, command substitution and
       arithmetic expansion), but not filename generation.

       If the option GLOB_SUBST  is  set,  the  result  of  any  unquoted  command  substitution,
       including the special form just mentioned, is eligible for filename generation.


       A  string  of  the  form  `$[exp]'  or  `$((exp))'  is  substituted  with the value of the
       arithmetic expression exp.  exp is subjected to parameter expansion, command  substitution
       and arithmetic expansion before it is evaluated.  See the section `Arithmetic Evaluation'.


       A  string  of  the form `foo{xx,yy,zz}bar' is expanded to the individual words `fooxxbar',
       `fooyybar' and `foozzbar'.  Left-to-right order  is  preserved.   This  construct  may  be
       nested.  Commas may be quoted in order to include them literally in a word.

       An  expression  of the form `{n1..n2}', where n1 and n2 are integers, is expanded to every
       number between n1 and n2 inclusive.   If  either  number  begins  with  a  zero,  all  the
       resulting  numbers  will  be  padded  with  leading  zeroes to that minimum width, but for
       negative numbers the - character is also included in the width.  If  the  numbers  are  in
       decreasing order the resulting sequence will also be in decreasing order.

       An  expression  of the form `{n1..n2..n3}', where n1, n2, and n3 are integers, is expanded
       as above, but only every n3th number starting from n1 is output.  If n3  is  negative  the
       numbers  are  output  in reverse order, this is slightly different from simply swapping n1
       and n2 in the case that the step n3 doesn't evenly divide the range.  Zero padding can  be
       specified in any of the three numbers, specifying it in the third can be useful to pad for
       example `{-99..100..01}' which is not possible to specify by putting a 0 on either of  the
       first two numbers (i.e. pad to two characters).

       An  expression of the form `{c1..c2}', where c1 and c2 are single characters (which may be
       multibyte characters), is expanded to every character in  the  range  from  c1  to  c2  in
       whatever character sequence is used internally.  For characters with code points below 128
       this is US ASCII (this is the only  case  most  users  will  need).   If  any  intervening
       character  is not printable, appropriate quotation is used to render it printable.  If the
       character sequence is  reversed,  the  output  is  in  reverse  order,  e.g.  `{d..a}'  is
       substituted as `d c b a'.

       If  a  brace  expression matches none of the above forms, it is left unchanged, unless the
       option BRACE_CCL (an abbreviation for `brace character class') is set.  In that  case,  it
       is  expanded  to  a  list  of the individual characters between the braces sorted into the
       order of the characters in the ASCII character set (multibyte characters are not currently
       handled).   The  syntax  is  similar  to a [...] expression in filename generation: `-' is
       treated specially to denote a range of characters, but `^' or `!' as the  first  character
       is treated normally.  For example, `{abcdef0-9}' expands to 16 words 0 1 2 3 4 5 6 7 8 9 a
       b c d e f.

       Note that brace expansion is not part of filename  generation  (globbing);  an  expression
       such  as  */{foo,bar}  is  split  into  two separate words */foo and */bar before filename
       generation takes place.  In particular, note that this is liable to produce a  `no  match'
       error  if  either  of  the  two  expressions does not match; this is to be contrasted with
       */(foo|bar), which is treated as a single pattern but otherwise has similar effects.

       To combine brace expansion with array expansion, see the ${^spec} form  described  in  the
       section Parameter Expansion above.


       Each  word is checked to see if it begins with an unquoted `~'.  If it does, then the word
       up to a `/', or the end of the word if there is no `/', is checked to see  if  it  can  be
       substituted  in  one  of  the  ways  described  here.  If so, then the `~' and the checked
       portion are replaced with the appropriate substitute value.

       A `~' by itself is replaced by the value of $HOME.  A `~' followed by a `+' or  a  `-'  is
       replaced by current or previous working directory, respectively.

       A  `~' followed by a number is replaced by the directory at that position in the directory
       stack.  `~0' is equivalent to `~+', and `~1' is the top of the stack.  `~+' followed by  a
       number  is  replaced  by  the directory at that position in the directory stack.  `~+0' is
       equivalent to `~+', and `~+1' is the top of the stack.   `~-'  followed  by  a  number  is
       replaced  by the directory that many positions from the bottom of the stack.  `~-0' is the
       bottom of the stack.  The PUSHD_MINUS option exchanges the effects of `~+' and `~-'  where
       they are followed by a number.

   Dynamic named directories
       If     the     function    zsh_directory_name    exists,    or    the    shell    variable
       zsh_directory_name_functions exists and contains an array  of  function  names,  then  the
       functions  are  used  to  implement  dynamic directory naming.  The functions are tried in
       order until one returns status zero, so it is important that functions test  whether  they
       can handle the case in question and return an appropriate status.

       A  `~'  followed  by a string namstr in unquoted square brackets is treated specially as a
       dynamic directory name.  Note that  the  first  unquoted  closing  square  bracket  always
       terminates  namstr.   The  shell function is passed two arguments: the string n (for name)
       and namstr.  It should either set the array  reply  to  a  single  element  which  is  the
       directory corresponding to the name and return status zero (executing an assignment as the
       last statement is usually sufficient), or it should return status non-zero.  In the former
       case the element of reply is used as the directory; in the latter case the substitution is
       deemed to have failed.  If all functions fail and the option  NOMATCH  is  set,  an  error

       The  functions  defined  as above are also used to see if a directory can be turned into a
       name, for example when printing the directory stack or when expanding %~ in  prompts.   In
       this  case  each  function  is  passed two arguments: the string d (for directory) and the
       candidate for dynamic naming.  The function should either return non-zero status,  if  the
       directory  cannot be named by the function, or it should set the array reply to consist of
       two elements: the first is the dynamic name for the  directory  (as  would  appear  within
       `~[...]'),  and  the  second  is  the  prefix length of the directory to be replaced.  For
       example, if  the  trial  directory  is  /home/myname/src/zsh  and  the  dynamic  name  for
       /home/myname/src (which has 16 characters) is s, then the function sets

              reply=(s 16)

       The  directory  name  so  returned is compared with possible static names for parts of the
       directory path, as described below; it is used if the prefix length  matched  (16  in  the
       example) is longer than that matched by any static name.

       It  is  not  a  requirement that a function implements both n and d calls; for example, it
       might be appropriate for certain dynamic forms of expansion not to be contracted to names.
       In  that  case  any  call  with  the first argument d should cause a non-zero status to be

       The completion system  calls  `zsh_directory_name  c'  followed  by  equivalent  calls  to
       elements  of  the  array  zsh_directory_name_functions, if it exists, in order to complete
       dynamic names for directories.  The code for this should be as for  any  other  completion
       function as described in zshcompsys(1).

       As a working example, here is a function that expands any dynamic names beginning with the
       string p: to directories below /home/pws/perforce.  In this simple case a static name  for
       the directory would be just as effective.

              zsh_directory_name() {
                emulate -L zsh
                setopt extendedglob
                local -a match mbegin mend
                if [[ $1 = d ]]; then
                  # turn the directory into a name
                  if [[ $2 = (#b)(/home/pws/perforce/)([^/]##)* ]]; then
                    typeset -ga reply
                    reply=(p:$match[2] $(( ${#match[1]} + ${#match[2]} )) )
                    return 1
                elif [[ $1 = n ]]; then
                  # turn the name into a directory
                  [[ $2 != (#b)p:(?*) ]] && return 1
                  typeset -ga reply
                elif [[ $1 = c ]]; then
                  # complete names
                  local expl
                  local -a dirs
                  _wanted dynamic-dirs expl 'dynamic directory' compadd -S\] -a dirs
                  return 1
                return 0

   Static named directories
       A  `~'  followed  by anything not already covered consisting of any number of alphanumeric
       characters or underscore (`_'), hyphen (`-'), or  dot  (`.')  is  looked  up  as  a  named
       directory,  and replaced by the value of that named directory if found.  Named directories
       are typically home directories for users on the system.  They may also be defined  if  the
       text  after the `~' is the name of a string shell parameter whose value begins with a `/'.
       Note that trailing slashes will be removed from the path  to  the  directory  (though  the
       original parameter is not modified).

       It is also possible to define directory names using the -d option to the hash builtin.

       When  the  shell  prints  a  path  (e.g. when expanding %~ in prompts or when printing the
       directory stack), the path is checked to see if it has a named directory  as  its  prefix.
       If  so,  then  the  prefix  portion  is  replaced  with  a `~' followed by the name of the
       directory.  The shorter of the two ways of referring to the directory is used, i.e. either
       the  directory  name  or the full path; the name is used if they are the same length.  The
       parameters $PWD and $OLDPWD are never abbreviated in this fashion.

   `=' expansion
       If a word begins with an unquoted `=' and the EQUALS option is set, the remainder  of  the
       word  is  taken  as  the name of a command.  If a command exists by that name, the word is
       replaced by the full pathname of the command.

       Filename expansion is performed  on  the  right  hand  side  of  a  parameter  assignment,
       including  those  appearing after commands of the typeset family.  In this case, the right
       hand side will be treated as a colon-separated list in the manner of the  PATH  parameter,
       so that a `~' or an `=' following a `:' is eligible for expansion.  All such behaviour can
       be disabled by quoting the `~', the `=', or the  whole  expression  (but  not  simply  the
       colon); the EQUALS option is also respected.

       If  the  option  MAGIC_EQUAL_SUBST  is  set,  any  unquoted  shell  argument  in  the form
       `identifier=expression' becomes eligible for file expansion as described in  the  previous
       paragraph.  Quoting the first `=' also inhibits this.


       If  a word contains an unquoted instance of one of the characters `*', `(', `|', `<', `[',
       or `?', it is regarded as a pattern for filename generation, unless  the  GLOB  option  is
       unset.   If  the  EXTENDED_GLOB  option  is  set, the `^' and `#' characters also denote a
       pattern; otherwise they are not treated specially by the shell.

       The word is replaced with a list of sorted  filenames  that  match  the  pattern.   If  no
       matching  pattern  is found, the shell gives an error message, unless the NULL_GLOB option
       is set, in which case the word is deleted; or unless the NOMATCH option is unset, in which
       case the word is left unchanged.

       In  filename generation, the character `/' must be matched explicitly; also, a `.' must be
       matched explicitly at the beginning of a pattern or after  a  `/',  unless  the  GLOB_DOTS
       option  is  set.   No filename generation pattern matches the files `.' or `..'.  In other
       instances of pattern matching, the `/' and `.' are not treated specially.

   Glob Operators
       *      Matches any string, including the null string.

       ?      Matches any character.

       [...]  Matches any of the enclosed characters.  Ranges of characters can be  specified  by
              separating two characters by a `-'.  A `-' or `]' may be matched by including it as
              the first character  in  the  list.   There  are  also  several  named  classes  of
              characters,  in the form `[:name:]' with the following meanings.  The first set use
              the macros provided by the  operating  system  to  test  for  the  given  character
              combinations,  including  any  modifications  due  to  local language settings, see

                     The character is alphanumeric

                     The character is alphabetic

                     The character is 7-bit, i.e. is a single-byte character without the top  bit

                     The character is a blank character

                     The character is a control character

                     The character is a decimal digit

                     The character is a printable character other than whitespace

                     The character is a lowercase letter

                     The character is printable

                     The character is printable but neither alphanumeric nor whitespace

                     The character is whitespace

                     The character is an uppercase letter

                     The character is a hexadecimal digit

              Another  set  of  named  classes  is  handled  internally  by  the shell and is not
              sensitive to the locale:

                     The character is allowed to form part of  a  shell  identifier,  such  as  a
                     parameter name

                     The  character is used as an input field separator, i.e. is contained in the
                     IFS parameter

                     The character is an IFS white space character; see the documentation for IFS
                     in the zshparam(1) manual page.

                     Matches  a  byte  that  starts an incomplete multibyte character.  Note that
                     there may be a sequence of more than one bytes that taken together form  the
                     prefix  of a multibyte character.  To test for a potentially incomplete byte
                     sequence, use the pattern `[[:INCOMPLETE:]]*'.   This  will  never  match  a
                     sequence starting with a valid multibyte character.

                     Matches  a  byte that does not start a valid multibyte character.  Note this
                     may be a continuation byte of an incomplete multibyte character as any  part
                     of  a  multibyte  string  consisting  of  invalid  and  incomplete multibyte
                     characters is treated as single bytes.

                     The character is treated as part of a word; this test is  sensitive  to  the
                     value of the WORDCHARS parameter

              Note  that  the  square brackets are additional to those enclosing the whole set of
              characters, so to test for a single alphanumeric character you need  `[[:alnum:]]'.
              Named character sets can be used alongside other types, e.g. `[[:alpha:]0-9]'.

       [!...] Like [...], except that it matches any character which is not in the given set.

              Matches  any  number  in the range x to y, inclusive.  Either of the numbers may be
              omitted to make the range open-ended; hence `<->' matches  any  number.   To  match
              individual digits, the [...] form is more efficient.

              Be  careful  when  using  other  wildcards  adjacent  to patterns of this form; for
              example, <0-9>* will actually match any number  whatsoever  at  the  start  of  the
              string,  since  the  `<0-9>' will match the first digit, and the `*' will match any
              others.  This is a trap for the unwary, but is in fact an inevitable consequence of
              the  rule  that  the  longest  possible match always succeeds.  Expressions such as
              `<0-9>[^[:digit:]]*' can be used instead.

       (...)  Matches the enclosed pattern.  This is used for grouping.  If the  KSH_GLOB  option
              is  set,  then a `@', `*', `+', `?' or `!' immediately preceding the `(' is treated
              specially, as detailed below. The option SH_GLOB  prevents  bare  parentheses  from
              being used in this way, though the KSH_GLOB option is still available.

              Note  that grouping cannot extend over multiple directories: it is an error to have
              a `/' within a group (this only applies for patterns used in filename  generation).
              There  is  one exception:  a group of the form (pat/)# appearing as a complete path
              segment can match a sequence of directories.  For  example,  foo/(a*/)#bar  matches
              foo/bar, foo/any/bar, foo/any/anyother/bar, and so on.

       x|y    Matches either x or y.  This operator has lower precedence than any other.  The `|'
              character must be within parentheses, to avoid interpretation as a  pipeline.   The
              alternatives are tried in order from left to right.

       ^x     (Requires  EXTENDED_GLOB  to be set.)  Matches anything except the pattern x.  This
              has a higher precedence than `/', so `^foo/bar'  will  search  directories  in  `.'
              except `./foo' for a file named `bar'.

       x~y    (Requires  EXTENDED_GLOB to be set.)  Match anything that matches the pattern x but
              does not match y.  This has lower precedence  than  any  operator  except  `|',  so
              `*/*~foo/bar' will search for all files in all directories in `.'  and then exclude
              `foo/bar' if there was  such  a  match.   Multiple  patterns  can  be  excluded  by
              `foo~bar~baz'.  In the exclusion pattern (y), `/' and `.' are not treated specially
              the way they usually are in globbing.

       x#     (Requires EXTENDED_GLOB to be set.)   Matches  zero  or  more  occurrences  of  the
              pattern  x.   This  operator  has  high precedence; `12#' is equivalent to `1(2#)',
              rather than `(12)#'.  It is an error for an unquoted `#' to follow something  which
              cannot  be  repeated;  this includes an empty string, a pattern already followed by
              `##', or parentheses when part of a KSH_GLOB pattern  (for  example,  `!(foo)#'  is
              invalid and must be replaced by `*(!(foo))').

       x##    (Requires EXTENDED_GLOB to be set.)  Matches one or more occurrences of the pattern
              x.  This operator has high precedence; `12##' is  equivalent  to  `1(2##)',  rather
              than  `(12)##'.  No more than two active `#' characters may appear together.  (Note
              the potential clash  with  glob  qualifiers  in  the  form  `1(2##)'  which  should
              therefore be avoided.)

   ksh-like Glob Operators
       If  the  KSH_GLOB option is set, the effects of parentheses can be modified by a preceding
       `@', `*', `+', `?' or `!'.  This character need not be unquoted to have  special  effects,
       but the `(' must be.

       @(...) Match the pattern in the parentheses.  (Like `(...)'.)

       *(...) Match  any  number of occurrences.  (Like `(...)#', except that recursive directory
              searching is not supported.)

       +(...) Match at least one occurrence.  (Like `(...)##', except  that  recursive  directory
              searching is not supported.)

       ?(...) Match zero or one occurrence.  (Like `(|...)'.)

       !(...) Match anything but the expression in parentheses.  (Like `(^(...))'.)

       The  precedence of the operators given above is (highest) `^', `/', `~', `|' (lowest); the
       remaining operators are simply treated from left to right as part of a  string,  with  `#'
       and `##' applying to the shortest possible preceding unit (i.e. a character, `?', `[...]',
       `<...>', or a parenthesised expression).  As mentioned above, a `/' used  as  a  directory
       separator  may  not appear inside parentheses, while a `|' must do so; in patterns used in
       other contexts than filename generation (for example, in case statements and tests  within
       `[[...]]'),  a  `/'  is  not  special;  and  `/' is also not special after a `~' appearing
       outside parentheses in a filename pattern.

   Globbing Flags
       There are various flags which affect any text  to  their  right  up  to  the  end  of  the
       enclosing  group  or to the end of the pattern; they require the EXTENDED_GLOB option. All
       take the form (#X) where X may have one of the following forms:

       i      Case insensitive:  upper or lower case characters in the  pattern  match  upper  or
              lower case characters.

       l      Lower  case  characters  in the pattern match upper or lower case characters; upper
              case characters in the pattern still only match upper case characters.

       I      Case sensitive:  locally negates the effect of i or l from that point on.

       b      Activate backreferences for parenthesised groups in the pattern; this does not work
              in  filename  generation.   When  a  pattern  with  a  set of active parentheses is
              matched, the strings matched by the groups are stored  in  the  array  $match,  the
              indices  of  the beginning of the matched parentheses in the array $mbegin, and the
              indices of the end in the array  $mend,  with  the  first  element  of  each  array
              corresponding  to  the  first parenthesised group, and so on.  These arrays are not
              otherwise special to the shell.  The  indices  use  the  same  convention  as  does
              parameter  substitution,  so  that  elements  of  $mend  and $mbegin may be used in
              subscripts; the KSH_ARRAYS option is respected.  Sets of  globbing  flags  are  not
              considered  parenthesised  groups;  only  the  first nine active parentheses can be

              For example,

                     foo="a string with a message"
                     if [[ $foo = (a|an)' '(#b)(*)' '* ]]; then
                       print ${foo[$mbegin[1],$mend[1]]}

              prints `string with a'.  Note that the first parenthesis is  before  the  (#b)  and
              does not create a backreference.

              Backreferences  work  with  all  forms  of  pattern  matching  other  than filename
              generation, but note that when performing matches  on  an  entire  array,  such  as
              ${array#pattern},  or  a  global substitution, such as ${param//pat/repl}, only the
              data for the last match remains available.  In the case of global replacements this
              may still be useful.  See the example for the m flag below.

              The  numbering  of  backreferences  strictly  follows  the  order  of  the  opening
              parentheses from left to right in the pattern string, although sets of  parentheses
              may  be  nested.   There are special rules for parentheses followed by `#' or `##'.
              Only the last match of the parenthesis is remembered: for example, in  `[[  abab  =
              (#b)([ab])#  ]]', only the final `b' is stored in match[1].  Thus extra parentheses
              may be necessary to match the complete segment: for example, use `X((ab|cd)#)Y'  to
              match a whole string of either `ab' or `cd' between `X' and `Y', using the value of
              $match[1] rather than $match[2].

              If the match fails none of the parameters is altered, so in some cases  it  may  be
              necessary  to  initialise  them  beforehand.  If some of the backreferences fail to
              match -- which happens if they are in an alternate branch which fails to match,  or
              if  they are followed by # and matched zero times -- then the matched string is set
              to the empty string, and the start and end indices are set to -1.

              Pattern matching with backreferences is slightly slower than without.

       B      Deactivate backreferences, negating the effect of the b flag from that point on.

       cN,M   The flag (#cN,M) can be used anywhere that the # or ## operators can be used except
              in  the  expressions  `(*/)#'  and  `(*/)##'  in filename generation, where `/' has
              special meaning; it cannot be combined with other globbing flags and a bad  pattern
              error  occurs  if  it  is misplaced.  It is equivalent to the form {N,M} in regular
              expressions.  The previous character or group is required to match between N and  M
              times,  inclusive.  The form (#cN) requires exactly N matches; (#c,M) is equivalent
              to specifying N as 0; (#cN,) specifies that there is no maximum limit on the number
              of matches.

       m      Set  references to the match data for the entire string matched; this is similar to
              backreferencing and does not work in filename generation.   The  flag  must  be  in
              effect at the end of the pattern, i.e. not local to a group. The parameters $MATCH,
              $MBEGIN and $MEND will be set to the string matched  and  to  the  indices  of  the
              beginning  and  end  of the string, respectively.  This is most useful in parameter
              substitutions, as otherwise the string matched is obvious.

              For example,

                     arr=(veldt jynx grimps waqf zho buck)
                     print ${arr//(#m)[aeiou]/${(U)MATCH}}

              forces all the matches (i.e. all  vowels)  into  uppercase,  printing  `vEldt  jynx
              grImps wAqf zhO bUck'.

              Unlike  backreferences, there is no speed penalty for using match references, other
              than the extra substitutions required for the replacement strings in cases such  as
              the example shown.

       M      Deactivate the m flag, hence no references to match data will be created.

       anum   Approximate  matching: num errors are allowed in the string matched by the pattern.
              The rules for this are described in the next subsection.

       s, e   Unlike the other flags, these have only a local effect, and each must appear on its
              own:  `(#s)' and `(#e)' are the only valid forms.  The `(#s)' flag succeeds only at
              the start of the test string, and the `(#e)' flag succeeds only at the end  of  the
              test  string; they correspond to `^' and `$' in standard regular expressions.  They
              are useful for matching path segments in patterns  other  than  those  in  filename
              generation  (where path segments are in any case treated separately).  For example,
              `*((#s)|/)test((#e)|/)*' matches a path segment `test'  in  any  of  the  following
              strings: test, test/at/start, at/end/test, in/test/middle.

              Another  use  is in parameter substitution; for example `${array/(#s)A*Z(#e)}' will
              remove only elements of an array which match the complete pattern `A*Z'.  There are
              other  ways  of performing many operations of this type, however the combination of
              the substitution operations `/' and `//' with the `(#s)' and `(#e)' flags  provides
              a single simple and memorable method.

              Note that assertions of the form `(^(#s))' also work, i.e. match anywhere except at
              the  start  of  the  string,  although  this  actually  means  `anything  except  a
              zero-length  portion  at  the  start of the string'; you need to use `(""~(#s))' to
              match a zero-length portion of the string not at the start.

       q      A `q' and everything up to the  closing  parenthesis  of  the  globbing  flags  are
              ignored  by the pattern matching code.  This is intended to support the use of glob
              qualifiers, see below.  The result is that the pattern `(#b)(*).c(#q.)' can be used
              both  for  globbing  and  for  matching  against a string.  In the former case, the
              `(#q.)' will be treated as a glob qualifier and the  `(#b)'  will  not  be  useful,
              while  in  the  latter case the `(#b)' is useful for backreferences and the `(#q.)'
              will be ignored.  Note that colon modifiers in the glob  qualifiers  are  also  not
              applied in ordinary pattern matching.

       u      Respect the current locale in determining the presence of multibyte characters in a
              pattern, provided the shell was compiled with  MULTIBYTE_SUPPORT.   This  overrides
              the  MULTIBYTE  option; the default behaviour is taken from the option.  Compare U.
              (Mnemonic: typically multibyte characters are from Unicode in the  UTF-8  encoding,
              although any extension of ASCII supported by the system library may be used.)

       U      All  characters  are considered to be a single byte long.  The opposite of u.  This
              overrides the MULTIBYTE option.

       For example, the test string fooxx can be matched by the pattern  (#i)FOOXX,  but  not  by
       (#l)FOOXX,    (#i)FOO(#I)XX   or   ((#i)FOOX)X.    The   string   (#ia2)readme   specifies
       case-insensitive matching of readme with up to two errors.

       When using the ksh syntax for grouping both KSH_GLOB and EXTENDED_GLOB must be set and the
       left  parenthesis should be preceded by @.  Note also that the flags do not affect letters
       inside [...] groups, in other  words  (#i)[a-z]  still  matches  only  lowercase  letters.
       Finally,  note  that when examining whole paths case-insensitively every directory must be
       searched for all files which match, so that a pattern  of  the  form  (#i)/foo/bar/...  is
       potentially slow.

   Approximate Matching
       When  matching  approximately,  the  shell keeps a count of the errors found, which cannot
       exceed the number specified in the (#anum) flags.  Four types of error are recognised:

       1.     Different characters, as in fooxbar and fooybar.

       2.     Transposition of characters, as in banana and abnana.

       3.     A character missing in the target string, as  with  the  pattern  road  and  target
              string rod.

       4.     An extra character appearing in the target string, as with stove and strove.

       Thus,  the  pattern  (#a3)abcd  matches dcba, with the errors occurring by using the first
       rule twice and the second once, grouping the string as [d][cb][a] and [a][bc][d].

       Non-literal parts of the pattern must match exactly,  including  characters  in  character
       ranges:  hence  (#a1)???   matches  strings of length four, by applying rule 4 to an empty
       part of the pattern, but not strings of length two, since all the  ?  must  match.   Other
       characters  which  must  match exactly are initial dots in filenames (unless the GLOB_DOTS
       option is set), and all slashes in filenames, so that a/bc is two errors  from  ab/c  (the
       slash  cannot  be  transposed  with  another  character).   Similarly,  errors are counted
       separately for non-contiguous strings in the pattern, so that (ab|cd)ef is two errors from

       When  using  exclusion  via  the  ~  operator,  approximate  matching  is treated entirely
       separately  for  the  excluded   part   and   must   be   activated   separately.    Thus,
       (#a1)README~READ_ME  matches  READ.ME  but not READ_ME, as the trailing READ_ME is matched
       without approximation.  However, (#a1)README~(#a1)READ_ME does not match  any  pattern  of
       the form READ?ME as all such forms are now excluded.

       Apart  from exclusions, there is only one overall error count; however, the maximum errors
       allowed may be altered locally, and this can  be  delimited  by  grouping.   For  example,
       (#a1)cat((#a0)dog)fox  allows  one error in total, which may not occur in the dog section,
       and the pattern (#a1)cat(#a0)dog(#a1)fox is equivalent.  Note that the point at  which  an
       error is first found is the crucial one for establishing whether to use approximation; for
       example, (#a1)abc(#a0)xyz will not match abcdxyz, because the error  occurs  at  the  `x',
       where approximation is turned off.

       Entire     path     segments     may     be     matched     approximately,     so     that
       `(#a1)/foo/d/is/available/at/the/bar' allows one error in any path segment.  This is  much
       less  efficient than without the (#a1), however, since every directory in the path must be
       scanned for a possible approximate match.  It is best to place the (#a1)  after  any  path
       segments which are known to be correct.

   Recursive Globbing
       A  pathname  component  of  the  form  `(foo/)#' matches a path consisting of zero or more
       directories matching the pattern foo.

       As a shorthand, `**/' is equivalent to `(*/)#'; note that this therefore matches files  in
       the current directory as well as subdirectories.  Thus:

              ls (*/)#bar


              ls **/bar

       does  a  recursive  directory search for files named `bar' (potentially including the file
       `bar' in  the  current  directory).   This  form  does  not  follow  symbolic  links;  the
       alternative  form  `***/'  does,  but  is  otherwise  identical.   Neither of these can be
       combined with other forms of globbing within the same path segment; in that case, the  `*'
       operators revert to their usual effect.

       Even  shorter forms are available when the option GLOB_STAR_SHORT is set.  In that case if
       no / immediately follows a ** or *** they are treated as if both a / plus a further *  are
       present.  Hence:

              setopt GLOBSTARSHORT
              ls **.c

       is equivalent to

              ls **/*.c

   Glob Qualifiers
       Patterns  used  for  filename  generation  may  end  in  a  list of qualifiers enclosed in
       parentheses.  The qualifiers specify  which  filenames  that  otherwise  match  the  given
       pattern will be inserted in the argument list.

       If  the option BARE_GLOB_QUAL is set, then a trailing set of parentheses containing no `|'
       or `(' characters (or `~' if it is special) is taken as a set of glob qualifiers.  A  glob
       subexpression  that would normally be taken as glob qualifiers, for example `(^x)', can be
       forced to be treated as part of the glob pattern by doubling the parentheses, in this case
       producing `((^x))'.

       If  the  option EXTENDED_GLOB is set, a different syntax for glob qualifiers is available,
       namely `(#qx)' where x is any of the same glob qualifiers used in the other  format.   The
       qualifiers  must  still  appear  at  the  end  of  the pattern.  However, with this syntax
       multiple glob qualifiers may be chained together.  They are treated as a  logical  AND  of
       the  individual sets of flags.  Also, as the syntax is unambiguous, the expression will be
       treated as glob qualifiers just as long any parentheses contained within it are  balanced;
       appearance  of  `|',  `(' or `~' does not negate the effect.  Note that qualifiers will be
       recognised in this form even if a bare glob qualifier exists at the end  of  the  pattern,
       for  example  `*(#q*)(.)' will recognise executable regular files if both options are set;
       however, mixed syntax should probably be avoided for  the  sake  of  clarity.   Note  that
       within  conditions  using the `[[' form the presence of a parenthesised expression (#q...)
       at the end of a string indicates that globbing should be  performed;  the  expression  may
       include  glob  qualifiers, but it is also valid if it is simply (#q).  This does not apply
       to the right hand side of pattern match  operators  as  the  syntax  already  has  special

       A qualifier may be any one of the following:

       /      directories

       F      `full'  (i.e. non-empty) directories.  Note that the opposite sense (^F) expands to
              empty directories and all non-directories.  Use (/^F) for empty directories.

       .      plain files

       @      symbolic links

       =      sockets

       p      named pipes (FIFOs)

       *      executable plain files (0100 or 0010 or 0001)

       %      device files (character or block special)

       %b     block special files

       %c     character special files

       r      owner-readable files (0400)

       w      owner-writable files (0200)

       x      owner-executable files (0100)

       A      group-readable files (0040)

       I      group-writable files (0020)

       E      group-executable files (0010)

       R      world-readable files (0004)

       W      world-writable files (0002)

       X      world-executable files (0001)

       s      setuid files (04000)

       S      setgid files (02000)

       t      files with the sticky bit (01000)

       fspec  files with access rights matching spec. This spec may be a octal number  optionally
              preceded  by  a  `=',  a  `+',  or a `-'. If none of these characters is given, the
              behavior is the same as for `='. The octal number describes the  mode  bits  to  be
              expected,  if  combined  with  a  `=',  the  value  given must match the file-modes
              exactly, with a `+', at least the bits in the given  number  must  be  set  in  the
              file-modes,  and  with  a `-', the bits in the number must not be set. Giving a `?'
              instead of a octal digit anywhere in the number ensures that the corresponding bits
              in the file-modes are not checked, this is only useful in combination with `='.

              If  the  qualifier  `f'  is followed by any other character anything up to the next
              matching character (`[', `{', and `<' match `]', `}',  and  `>'  respectively,  any
              other  character  matches  itself) is taken as a list of comma-separated sub-specs.
              Each sub-spec may be either an octal number as described above or a list of any  of
              the characters `u', `g', `o', and `a', followed by a `=', a `+', or a `-', followed
              by a list of any of the characters `r', `w', `x', `s', and `t', or an octal  digit.
              The  first  list  of characters specify which access rights are to be checked. If a
              `u' is given, those for the owner of the file are used, if a `g' is given, those of
              the  group  are checked, a `o' means to test those of other users, and the `a' says
              to test all three groups. The `=', `+', and `-' again says how the modes are to  be
              checked and have the same meaning as described for the first form above. The second
              list of characters finally says which access rights are to  be  expected:  `r'  for
              read  access,  `w'  for  write access, `x' for the right to execute the file (or to
              search a directory), `s' for the setuid and setgid bits, and  `t'  for  the  sticky

              Thus,  `*(f70?)'  gives  the files for which the owner has read, write, and execute
              permission, and for which other group members have no rights,  independent  of  the
              permissions  for  other users. The pattern `*(f-100)' gives all files for which the
              owner does not have execute permission, and `*(f:gu+w,o-rx:)' gives the  files  for
              which  the owner and the other members of the group have at least write permission,
              and for which other users don't have read or execute permission.

       +cmd   The string will be executed as shell code.  The filename will be  included  in  the
              list  if and only if the code returns a zero status (usually the status of the last

              In the first form, the first character after the `e' will be used  as  a  separator
              and  anything  up to the next matching separator will be taken  as the string; `[',
              `{', and `<' match `]', `}', and  `>',  respectively,  while  any  other  character
              matches  itself.  Note that expansions must be quoted in the string to prevent them
              from being expanded before globbing is done.  string  is  then  executed  as  shell
              code.   The  string globqual is appended to the array zsh_eval_context the duration
              of execution.

              During the execution of string the filename currently being tested is available  in
              the  parameter  REPLY; the parameter may be altered to a string to be inserted into
              the list instead of the original filename.  In addition, the parameter reply may be
              set  to  an  array  or  a string, which overrides the value of REPLY.  If set to an
              array, the latter is inserted into the command line word by word.

              For example, suppose a  directory  contains  a  single  file  `lonely'.   Then  the
              expression  `*(e:'reply=(${REPLY}{1,2})':)'  will  cause  the  words  `lonely1' and
              `lonely2' to be inserted into the command line.  Note the quoting of string.

              The form +cmd has the same effect, but no delimiters appear around  cmd.   Instead,
              cmd  is  taken  as  the  longest  sequence  of  characters following the + that are
              alphanumeric or underscore.  Typically cmd will be the name  of  a  shell  function
              that contains the appropriate test.  For example,

                     nt() { [[ $REPLY -nt $NTREF ]] }
                     ls -l *(+nt)

              lists  all  files  in  the  directory  that  have  been modified more recently than

       ddev   files on the device dev

              files having a link count less than ct (-), greater than ct (+), or equal to ct

       U      files owned by the effective user ID

       G      files owned by the effective group ID

       uid    files owned by user ID id if that is a number.   Otherwise,  id  specifies  a  user
              name:  the  character  after  the  `u'  will be taken as a separator and the string
              between it and the next matching separator will be  taken  as  a  user  name.   The
              starting separators `[', `{', and `<' match the final separators `]', `}', and `>',
              respectively; any other character matches itself.  The  selected  files  are  those
              owned  by this user.  For example, `u:foo:' or `u[foo]' selects files owned by user

       gid    like uid but with group IDs or names

              files accessed exactly n days ago.  Files accessed  within  the  last  n  days  are
              selected  using  a  negative value for n (-n).  Files accessed more than n days ago
              are selected by a positive n value (+n).  Optional unit specifiers `M',  `w',  `h',
              `m'  or  `s' (e.g. `ah5') cause the check to be performed with months (of 30 days),
              weeks, hours, minutes or seconds instead of days, respectively.   An  explicit  `d'
              for days is also allowed.

              Any  fractional part of the difference between the access time and the current part
              in the appropriate units  is  ignored  in  the  comparison.   For  instance,  `echo
              *(ah-5)' would echo files accessed within the last five hours, while `echo *(ah+5)'
              would echo files accessed at least six hours ago, as times  strictly  between  five
              and six hours are treated as five hours.

              like the file access qualifier, except that it uses the file modification time.

              like the file access qualifier, except that it uses the file inode change time.

              files less than n bytes (-), more than n bytes (+), or exactly n bytes in length.

              If  this flag is directly followed by a size specifier `k' (`K'), `m' (`M'), or `p'
              (`P') (e.g. `Lk-50') the check is performed with kilobytes,  megabytes,  or  blocks
              (of  512  bytes) instead.  (On some systems additional specifiers are available for
              gigabytes, `g' or `G', and terabytes, `t' or `T'.) If a size specifier  is  used  a
              file is regarded as "exactly" the size if the file size rounded up to the next unit
              is equal to the test size.  Hence `*(Lm1)' matches  files  from  1  byte  up  to  1
              Megabyte inclusive.  Note also that the set of files "less than" the test size only
              includes files that would not match the equality test; hence `*(Lm-1)' only matches
              files of zero size.

       ^      negates all qualifiers following it

       -      toggles  between making the qualifiers work on symbolic links (the default) and the
              files they point to

       M      sets the MARK_DIRS option for the current pattern

       T      appends a trailing qualifier mark to the filenames,  analogous  to  the  LIST_TYPES
              option, for the current pattern (overrides M)

       N      sets the NULL_GLOB option for the current pattern

       D      sets the GLOB_DOTS option for the current pattern

       n      sets the NUMERIC_GLOB_SORT option for the current pattern

       Yn     enables  short-circuit  mode:  the  pattern will expand to at most n filenames.  If
              more than n matches exist, only the first n matches in  directory  traversal  order
              will be considered.

              Implies oN when no oc qualifier is used.

       oc     specifies how the names of the files should be sorted. If c is n they are sorted by
              name; if it is L they are sorted depending on the size (length) of the files; if  l
              they  are  sorted by the number of links; if a, m, or c they are sorted by the time
              of the last access, modification, or inode change  respectively;  if  d,  files  in
              subdirectories  appear  before  those in the current directory at each level of the
              search -- this is best combined with other criteria, for example `odon' to sort  on
              names  for  files  within  the same directory; if N, no sorting is performed.  Note
              that a, m, and c compare the age against the current time, hence the first name  in
              the  list  is  the youngest file. Also note that the modifiers ^ and - are used, so
              `*(^-oL)' gives a list of all files  sorted  by  file  size  in  descending  order,
              following  any  symbolic  links.   Unless oN is used, multiple order specifiers may
              occur to resolve ties.

              The default sorting is n (by name) unless the Y glob qualifier is  used,  in  which
              case it is N (unsorted).

              oe and o+ are special cases; they are each followed by shell code, delimited as for
              the e glob qualifier and the + glob qualifier respectively (see above).   The  code
              is  executed  for each matched file with the parameter REPLY set to the name of the
              file on entry and globsort appended to zsh_eval_context.  The  code  should  modify
              the parameter REPLY in some fashion.  On return, the value of the parameter is used
              instead of the file name as the  string  on  which  to  sort.   Unlike  other  sort
              operators,  oe  and  o+  may  be repeated, but note that the maximum number of sort
              operators of any kind that may appear in any glob expression is 12.

       Oc     like `o', but sorts in descending order; i.e. `*(^oc)' is the same as  `*(Oc)'  and
              `*(^Oc)'  is  the  same as `*(oc)'; `Od' puts files in the current directory before
              those in subdirectories at each level of the search.

              specifies which of the matched filenames should be included in the  returned  list.
              The  syntax  is  the  same as for array subscripts. beg and the optional end may be
              mathematical expressions. As in parameter subscripting they may be negative to make
              them  count  from  the last match backward. E.g.: `*(-OL[1,3])' gives a list of the
              names of the three largest files.

              The string will be prepended to each glob match as  a  separate  word.   string  is
              delimited  in  the  same  way as arguments to the e glob qualifier described above.
              The qualifier can be repeated; the words  are  prepended  separately  so  that  the
              resulting  command line contains the words in the same order they were given in the
              list of glob qualifiers.

              A typical use for this is to prepend an option before all  occurrences  of  a  file
              name;  for  example, the pattern `*(P:-f:)' produces the command line arguments `-f
              file1 -f file2 ...'

              If the modifier ^ is active, then string will be  appended  instead  of  prepended.
              Prepending and appending is done independently so both can be used on the same glob
              expression; for example by writing  `*(P:foo:^P:bar:^P:baz:)'  which  produces  the
              command line arguments `foo baz file1 bar ...'

       More  than one of these lists can be combined, separated by commas. The whole list matches
       if at least one of the sublists matches (they are `or'ed, the qualifiers in  the  sublists
       are  `and'ed).  Some qualifiers, however, affect all matches generated, independent of the
       sublist in which they are given.  These are the qualifiers `M', `T', `N', `D',  `n',  `o',
       `O' and the subscripts given in brackets (`[...]').

       If  a  `:'  appears in a qualifier list, the remainder of the expression in parenthesis is
       interpreted  as  a  modifier  (see  the  section  `Modifiers'  in  the  section   `History
       Expansion').   Each  modifier  must  be  introduced by a separate `:'.  Note also that the
       result after modification does not have to be an existing file.  The name of any  existing
       file  can  be  followed  by  a  modifier  of  the form `(:...)' even if no actual filename
       generation is performed, although note that the presence of  the  parentheses  causes  the
       entire  expression  to  be  subjected  to  any  global  pattern  matching  options such as
       NULL_GLOB. Thus:

              ls *(-/)

       lists all directories and symbolic links that point to directories, and

              ls *(-@)

       lists all broken symbolic links, and

              ls *(%W)

       lists all world-writable device files in the current directory, and

              ls *(W,X)

       lists all files in the current directory that are world-writable or world-executable, and

              echo /tmp/foo*(u0^@:t)

       outputs the basename of all root-owned files beginning with  the  string  `foo'  in  /tmp,
       ignoring symlinks, and

              ls *.*~(lex|parse).[ch](^D^l1)

       lists  all  files  having  a  link  count  of one whose names contain a dot (but not those
       starting with a dot, since GLOB_DOTS is explicitly switched off) except for lex.c,  lex.h,
       parse.c and parse.h.

              print b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/)

       demonstrates  how  colon  modifiers  and  other  qualifiers  may be chained together.  The
       ordinary qualifier `.' is applied first, then the colon modifiers in order  from  left  to
       right.   So  if  EXTENDED_GLOB  is  set  and  the  base  pattern  matches the regular file, the shell will print `shmiltin.shmo'.