zshexpn



ZSHEXPN(1)                                                          ZSHEXPN(1)




NAME

       zshexpn - zsh expansion and substitution


DESCRIPTION

       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 one step in left-to-right fashion.
              After these expansions, all unquoted occurrences of the  charac-
              ters β€˜\’, β€˜β€β€™β€™ and β€˜"’ 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 expan-
              sion, preceding the set of five expansions mentioned above.

       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

       History  expansion  allows you to use words from previous command lines
       in the command line you are typing.  This simplifies  spelling  correc-
       tions and the repetition of complicated commands or arguments.  Immedi-
       ately 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 Prompt Expansion in zshmisc(1)) is
       the number that is to be assigned to the next command.


   Overview
       A history expansion begins with the first character  of  the  histchars
       parameter,  which is β€˜!’ by default, and may occur anywhere on the com-
       mand line; history expansions do not nest.  The β€˜!’ can be escaped with
       β€˜\’ or can be enclosed between a pair of single quotes (β€β€™β€β€™) to suppress
       its special meaning.  Double quotes will not work for this.   Following
       this history character is an optional event designator (see the section
       β€˜Event Designators’) and then an optional word designator (the  section
       β€˜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.

       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 previ-
       ous 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, β€˜!’ is the event designator for the previous  command,  so
       β€˜!!:1’  always  refers  to  the first word of the previous command, and
       β€˜!!$’ always refers to the last word of  the  previous  command.   With
       CSH_JUNKIE_HISTORY set, then β€˜!:1’ and β€˜!$’ function in the same manner
       as β€˜!!:1’ and β€˜!!$’, respectively.  Conversely,  if  CSH_JUNKIE_HISTORY
       is  unset,  then  β€˜!:1’  and  β€˜!$’  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 previ-
       ous command if there is no preceding reference.

       The character sequence β€˜^foo^bar’ (where β€˜^’  is  actually  the  second
       character of the histchars parameter) repeats the last command, replac-
       ing the string foo with bar.  More precisely, the sequence  β€˜^foo^bar^’
       is synonymous with β€˜!!:s^foo^bar^’, hence other modifiers (see the sec-
       tion β€˜Modifiers’) may follow the final β€˜^’.

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

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

   Event Designators
       An event designator is a reference to a command-line entry in the  his-
       tory  list.   In  the list below, remember that the initial β€β€˜!β€β€™ in each
       item may be changed to  another  character  by  setting  the  histchars
       parameter.

       !      Start a history expansion, except when followed by a blank, new-
              line, β€˜=’ or β€˜(’.  If followed immediately by a word  designator
              (see  the section β€˜Word Designators’), this forms a history ref-
              erence with no event designator (see the section β€˜Overview’).

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

       !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.

       !?str[?]
              Refer  to  the most recent command containing str.  The trailing
              β€˜?’ is necessary if this reference is to be followed by a  modi-
              fier  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 β€˜!#’ reference.

       !{...} Insulate a history reference from adjacent characters (if neces-
              sary).

   Word Designators
       A word designator indicates which word or words of a given command line
       are to be included in a history reference.  A β€˜:’ usually separates the
       event  specification  from the word designator.  It may be omitted only
       if the word designator begins with a β€˜^’, β€˜$’, β€˜*’, β€˜-’ or  β€˜%’.   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 β€˜x-$’.
       x-     Like β€˜x*’ but omitting word $.

       Note  that  a  β€˜%’ word designator works only when used in one of β€˜!%’,
       β€˜!:%’ or β€˜!?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.

   Modifiers
       After the optional word designator, you can add a sequence  of  one  or
       more  of  the following modifiers, each preceded by a β€˜:’.  These modi-
       fiers also work on the result  of  filename  generation  and  parameter
       expansion, except where noted.

       h      Remove  a  trailing  pathname component, leaving the head.  This
              works like β€˜dirname’.

       r      Remove a filename extension of the form β€˜.xxx’, leaving the root
              name.

       e      Remove all but the extension.

       t      Remove  all leading pathname components, leaving the tail.  This
              works like β€˜basename’.

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

       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.

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

       l      Convert the words to all lowercase.

       u      Convert the words to all uppercase.

       s/l/r[/]
              Substitute  r for l as described below.  Unless preceded immedi-
              ately by a g, with no colon between, 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.

       &      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.

       The s/l/r/ substitution works as follows.  The left-hand side  of  sub-
       stitutions  are  not  regular  expressions, but character strings.  Any
       character can be used as the delimiter in place of  β€˜/’.   A  backslash
       quotes   the   delimiter   character.    The   character  β€˜&’,  in  the
       right-hand-side r, is replaced by the text from the  left-hand-side  l.
       The  β€˜&’  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  β€˜!?s’.  You can omit the rightmost delimiter if a newline immedi-
       ately follows r; the rightmost β€˜?’ in a context scan can  similarly  be
       omitted.  Note the same record of the last l and r is maintained across
       all forms of expansion.

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

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

       F:expr:
              Like  f,  but repeats only n times if the expression expr evalu-
              ates to n.  Any character can be used instead  of  the  β€˜:’;  if
              β€˜(’,  β€˜[’,  or β€˜{’ is used as the opening delimiter, the closing
              delimiter should be ’)’, β€˜]’, or β€˜}’, 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 β€˜:’; opening parentheses are handled specially, see above.


PROCESS SUBSTITUTION

       Each  command argument of the form β€˜<(list)’, β€˜>(list)’ or β€˜=(list)’ is
       subject to process substitution.  In the case of the < or > forms,  the
       shell  runs  process  list  asynchronously.  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  pro-
       cess2.

       If  =(...)  is used instead of <(...), then the file passed as an argu-
       ment 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.

       The = form is useful as both the /dev/fd and the named pipe implementa-
       tion 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 sub-
       shell 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 effi-
       ciently 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  pro-
       cess 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  asyn-
       chronously.  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 completion.



PARAMETER EXPANSION

       The character β€˜$’ is used to introduce parameter expansions.  See  zsh-
       param(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  β€˜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  β€˜Modifiers’ in the section β€˜History Expansion’ can be
       applied:  for example, ${i:s/foo/bar/} performs string substitution  on
       the expansion of parameter $i.

       ${name}
              The  value,  if  any, of the parameter name is substituted.  The
              braces are required if the expansion is to be followed by a let-
              ter,  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  sub-
              script  or  any colon modifiers appearing after the name, or any
              of the characters β€˜^’, β€˜=’, β€˜~’, β€˜#’ or β€˜+’ 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.

       ${+name}
              If name is the name of a set parameter β€˜1’ is substituted,  oth-
              erwise β€˜0’ is substituted.

       ${name:-word}
              If name is set and is non-null then substitute its value; other-
              wise substitute word. If name is missing, substitute word.

       ${name:=word}
       ${name::=word}
              In the first form, if name is unset or is null then  set  it  to
              word;  in the second form, unconditionally set name to word.  In
              both forms, the value of the parameter is then substituted.

       ${name:?word}
              If name is set and is non-null then substitute its value; other-
              wise,  print  word  and exit from the shell.  Interactive shells
              instead return to the prompt.  If word is omitted, then a  stan-
              dard message is printed.

       ${name:+word}
              If  name  is set and is non-null then substitute word; otherwise
              substitute nothing.

       If the colon is omitted from one of the above expressions containing  a
       colon,  then the shell only checks whether name is set, not whether its
       value is null.

       In the following expressions, when name is an array and  the  substitu-
       tion is not quoted, or if the β€˜(@)’ flag or the name[@] syntax is used,
       matching and replacement is performed on each array element separately.

       ${name#pattern}
       ${name##pattern}
              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.

       ${name%pattern}
       ${name%%pattern}
              If  the  pattern matches the end of the value of name, then sub-
              stitute the value of name with the matched portion deleted; oth-
              erwise,  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.

       ${name:#pattern}
              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 β€˜(M)’ flag to remove the non-matched elements).

       ${name/pattern/repl}
       ${name//pattern/repl}
              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.   Both
              pattern  and  repl are subject to double-quoted substitution, so
              that expressions like ${name/$opat/$npat} will  work,  but  note
              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 β€˜#’, in which case the pattern must
              match at the start of the string, or β€˜%’, in which case it  must
              match  at  the  end  of  the  string.   The repl may be an empty
              string, in which case the final β€˜/’ may  also  be  omitted.   To
              quote  the  final  β€˜/’ in other cases it should be preceded by a
              single backslash; this is not necessary if the β€˜/’ occurs inside
              a substituted parameter.  Note also that the β€˜#’ and β€˜%’ are not
              active if they occur inside a substituted parameter, even at the
              start.

              The  first β€˜/’ may be preceded by a β€˜:’, in which case the match
              will only succeed if it matches the entire word.  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 β€˜~’ ensures that the text of $sub is treated as a pat-
              tern rather than a plain string.  In the first case, the longest
              match for t*e is substituted and the result is β€˜spy star’, while
              in  the  second  case,  the  shortest  matches are taken and the
              result is β€˜spy spy lispy star’.

       ${#spec}
              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.  Note that β€˜^’, β€˜=’, and β€˜~’, below, must appear
              to the left of β€˜#’ when these forms are combined.

       ${^spec}
              Turn on the RC_EXPAND_PARAM option for the evaluation  of  spec;
              if  the  β€˜^’  is doubled, turn it off.  When this option is set,
              array expansions of the form foo${xx}bar, where the parameter xx
              is  set  to  (a  b  c),  are  substituted  with β€˜fooabar foobbar
              foocbar’ instead of the default β€˜fooa b cbar’.

              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 sec-
              tion  β€˜Brace  Expansion’  below.   If  word splitting is also in
              effect the $var[N] may themselves be split into  different  list
              elements.

       ${=spec}
              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 β€˜=’ 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.

       ${~spec}
              Turn on the GLOB_SUBST option for the evaluation of spec; if the
              β€˜~’  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 β€˜=’ and β€˜!=’ operators in conditions.

       If  a ${...} type parameter expression or a $(...) type command substi-
       tution 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 β€˜head’ and β€˜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 $(foo), but the flag β€˜(f)’ (see
       below) is applied using the rules for unquoted expansions.   Note  fur-
       ther that quotes are themselves nested in this context; for example, in
       "${(@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 rep-
       etitions need not be consecutive; for example, β€˜(q%q%q)’ means the same
       thing as the more readable β€˜(%%qqq)’.  The  following  flags  are  sup-
       ported:

       %      Expand  all  % escapes in the resulting words in the same way as
              in in prompts (see the section β€˜Prompt Expansion’). If this flag
              is  given  twice, full prompt expansion is done on the resulting
              words,  depending  on  the  setting   of   the   PROMPT_PERCENT,
              PROMPT_SUBST and PROMPT_BANG options.

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

       A      Create  an  array  parameter with β€˜${...=...}’, β€˜${...:=...}’ or
              β€˜${...::=...}’.  If this flag is repeated (as in  β€˜AA’),  create
              an associative array parameter.  Assignment is made before sort-
              ing or padding.  The name part may be a  subscripted  range  for
              ordinary  arrays;  the  word part must be converted to an array,
              for example by using β€˜${(AA)=name=...}’ to activate field split-
              ting, when creating an associative array.

       a      With o or O, sort in array index order. Note that β€˜oa’ is there-
              fore equivalent to the default but β€˜Oa’ is useful for  obtaining
              an array’s elements in reverse order.

       c      With ${#name}, count the total number of characters in an array,
              as if the elements were concatenated with spaces between them.

       C      Capitalize the resulting words.  β€˜Words’ in this case refers  to
              sequences  of  alphanumeric characters separated by non-alphanu-
              merics, not to words that result from field splitting.

       e      Perform 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 to lines. This is a  shorthand
              for β€˜ps:\n:’.

       F      Join  the words of arrays together using newline as a separator.
              This is a shorthand for β€˜pj:\n:’.

       i      With o or O, sort case-independently.

       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 val-
              ues.  However, this flag may  not  be  combined  with  subscript
              ranges.

       L      Convert all letters in the result to lower case.

       n      With o or O, sort numerically.

       o      Sort the resulting words in ascending order.

       O      Sort the resulting words in descending order.

       P      This forces the value of the parameter name to be interpreted as
              a further parameter name, whose value will be used where  appro-
              priate. 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 β€˜foo=bar’ and β€˜bar=baz’, the
              strings ${(P)foo}, ${(P)${foo}}, and ${(P)$(echo bar)}  will  be
              expanded to β€˜baz’.

       q      Quote  the  resulting  words  with  backslashes. 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. If it is given four times, the words are quoted in  sin-
              gle quotes preceded by a $.

       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  con-
              sists  of keywords separated by hyphens (β€˜-’). The first keyword
              in the string  describes  the  main  type,  it  can  be  one  of
              β€˜scalar’,  β€˜array’,  β€˜integer’,  β€˜float’  or  β€˜association’. The
              other keywords describe the type in more detail:

              local  for local parameters

              left   for left justified parameters

              right_blanks
                     for right justified parameters with leading blanks

              right_zeros
                     for right justified parameters with leading zeros

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

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

              readonly
                     for readonly parameters

              tag    for tagged parameters

              export for exported parameters

              unique for arrays which keep only the first occurrence of dupli-
                     cated values

              hide   for parameters with the β€˜hide’ flag

              special
                     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 sub-
              scripts,  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 and  e  flags
              or  the  pattern  matching  forms  such as β€˜${name#pattern}’ are
              reported. Without the flag they 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.

              Note that this is done very late, as for the β€˜(s)’ flag.  So  to
              access  single words in the result, one has to use nested expan-
              sions as in β€˜${${(z)foo}[2]}’. Likewise, to remove the quotes in
              the resulting words one would do: β€˜${(Q)${(z)foo}}’.

       The following flags (except p) are followed by one or more arguments as
       shown.  Any character, or the matching pairs β€˜(...)’, β€˜{...}’, β€˜[...]’,
       or  β€˜<...>’,  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 delim-
       iters must surround each argument.

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

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

       l:expr::string1::string2:
              Pad the resulting words on the left.  Each word  will  be  trun-
              cated  if  required  and placed in a field expr characters wide.
              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,  this  string  is  inserted  once
              directly to the left of each word, before padding.

       r:expr::string1::string2:
              As  l,  but pad the words on the right and insert string2 on the
              right.

       s:string:
              Force field splitting (see the option SH_WORD_SPLIT) at the sep-
              arator  string.   Note  that  a string of two or more characters
              means all must all match in  sequence;  this  differs  from  the
              treatment of two or more characters in the IFS parameter.

       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.

       I:expr:
              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  substi-
              tuted)  or  ${...//...} (all matches from the exprth on are sub-
              stituted).  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  replace-
              ments  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 for-
              ward 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  β€˜which’, β€˜witch’, β€˜witch’ and
              β€˜wich’; the form using β€˜##’ will match and remove β€˜which  switch
              is the right switch for Ipswich’, β€˜witch is the right switch for
              Ipswich’, β€˜witch for Ipswich’ and β€˜wich’.  The  form  using  β€˜%’
              will  remove  the same matches as for β€˜#’, but in reverse order,
              and the form using β€˜%%’ will remove the same matches as for β€˜##’
              in reverse order.

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

       E      Include the index of the end of the match in the result.

       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).


   Rules
       Here  is  a  summary  of  the rules for substitution; this assumes that
       braces are present around the substitution, i.e. ${...}.  Some particu-
       lar  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  substi-
              tution 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 substitu-
              tion, 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 β€˜(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}.

       2. 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;  subse-
              quent  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.

       3. Parameter Name Replacement
              The effect of any (P) flag, which treats the value so far  as  a
              parameter  name and replaces it with the corresponding value, is
              applied.

       4. Double-Quoted Joining
              If the value after this process is an array, and  the  substitu-
              tion appears in double quotes, and no (@) flag is present at the
              current level, the 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.

       5. 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 2., 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).

       6. Modifiers
              Any  modifiers, as specified by a trailing β€˜#’, β€˜%’, β€˜/’ (possi-
              bly doubled) or by a set of modifiers of the form :... (see  the
              section  β€˜Modifiers’  in  the  section β€˜History Expansion’), are
              applied to the words of the value at this level.

       7. Forced Joining
              If the β€˜(j)’ flag is present, or no β€˜(j)’ flag  is  present  but
              the  string is to be split as given by rules 8. or 9., and join-
              ing did not take place at step 4., any words in  the  value  are
              joined together using the given string or the first character of
              $IFS if none.  Note that the β€˜(F)’ flag  implicitly  supplies  a
              string for joining in this manner.

       8. Forced Splitting
              If  one  of  the β€˜(s)’, β€˜(f)’ or β€˜(z)’ flags are present, or the
              β€˜=’ 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.

       9. Shell Word Splitting
              If no β€˜(s)’, β€˜(f)’ or β€˜=’ was given, but the word is not  quoted
              and the option SH_WORD_SPLIT is set, the word is split on occur-
              rences of any of the characters in $IFS.  Note this  step,  too,
              takes place at all levels of a nested substitution.

       10. Re-Evaluation
              Any  β€˜(e)’  flag  is  applied  to  the  value,  forcing it to be
              re-examined for new parameter substitutions, but also  for  com-
              mand and arithmetic substitutions.

       11. Padding
              Any padding of the value by the β€˜(l.fill.)’ or β€˜(r.fill.)’ flags
              is applied.

       12. 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 β€˜${(P)${(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.


   Examples
       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.   Com-
       pare  this with the effect of $(<file) alone, which divides the file up
       by words, or the same inside double quotes, which makes the entire con-
       tent of the file a single string.

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

       "${(@)${foo}[1]}"
              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 β€˜(@)’ flag) the sub-
              script picks the first character.

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

       As an example of the rules for word splitting and joining, suppose $foo
       contains the array β€˜(ax1 bx1)’.  Then

       ${(s/x/)foo}
              produces the words β€˜a’, β€˜1 b’ and β€˜1’.

       ${(j/x/s/x/)foo}
              produces β€˜a’, β€˜1’, β€˜b’ and β€˜1’.

       ${(s/x/)foo%%1*}
              produces  β€˜a’  and β€˜ 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 β€˜a’, β€˜ b’  and  β€˜β€™.   The  final
              empty string will then be elided, as it is not in double quotes.



COMMAND SUBSTITUTION

       A command enclosed in parentheses  preceded  by  a  dollar  sign,  like
       β€˜$(...)’,  or quoted with grave accents, like β€˜β€β€˜...β€β€˜β€™, is replaced with
       its standard output, with any trailing newlines deleted.  If  the  sub-
       stitution  is  not enclosed in double quotes, the output is broken into
       words using the IFS parameter.  The substitution β€˜$(cat  foo)’  may  be
       replaced  by  the  equivalent but faster β€˜$(<foo)’.  In either case, if
       the option GLOB_SUBST is set, the output is eligible for filename  gen-
       eration.


ARITHMETIC EXPANSION

       A  string  of  the  form β€˜$[exp]’ or β€˜$((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 β€˜Arithmetic Evaluation’.


BRACE EXPANSION

       A string of the form β€˜foo{xx,yy,zz}bar’ is expanded to  the  individual
       words  β€˜fooxxbar’,  β€˜fooyybar’  and β€˜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 β€˜{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 lead-
       ing zeroes to that minimum width.  If the  numbers  are  in  decreasing
       order the resulting sequence will also be in decreasing order.

       If  a  brace  expression  matches  none  of the above forms, it is left
       unchanged, unless the BRACE_CCL option is set.  In  that  case,  it  is
       expanded  to  a  sorted  list  of the individual characters between the
       braces, in the manner of a search set.  β€˜-’ is treated specially as  in
       a  search  set,  but  β€˜^’ or β€˜!’ as the first character is treated nor-
       mally.

       Note that brace expansion is not part  of  filename  generation  (glob-
       bing);  an  expression  such  as */{foo,bar} is split into two separate
       words */foo and */bar before filename generation takes place.  In  par-
       ticular,  note  that  this  is  liable to produce a β€˜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.


FILENAME EXPANSION

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

       A β€˜~’ by itself is replaced by the value of $HOME.  A β€˜~’ followed by a
       β€˜+’ or a β€˜-’ is replaced by the value of $PWD or $OLDPWD, respectively.

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

       A β€˜~’ followed by anything not already covered 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  sys-
       tem.  They may also be defined if the text after the β€˜~’ is the name of
       a string shell parameter whose value begins with a  β€˜/’.   It  is  also
       possible  to  define  directory  names  using the -d option to the hash
       builtin.

       In certain circumstances (in prompts, for  instance),  when  the  shell
       prints  a  path, 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  β€˜~’
       followed  by  the name of the directory.  The shortest way of referring
       to the directory is used, with ties broken in favour of using  a  named
       directory,  except when the directory is / itself.  The parameters $PWD
       and $OLDPWD are never abbreviated in this fashion.

       If a word begins with an unquoted β€˜=’ 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 β€˜~’
       or  an  β€˜=’  following  a  β€˜:’  is  eligible  for  expansion.  All such
       behaviour can be disabled by quoting the β€˜~’, the  β€˜=’,  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 β€˜identifier=expression’ becomes eligible for file expansion as
       described in the  previous  paragraph.   Quoting  the  first  β€˜=’  also
       inhibits this.


FILENAME GENERATION

       If  a  word contains an unquoted instance of one of the characters β€˜*’,
       β€˜(’, β€˜|’, β€˜<’, β€˜[’, or β€˜?’, it is regarded as a  pattern  for  filename
       generation,  unless  the  GLOB  option  is unset.  If the EXTENDED_GLOB
       option is set, the β€˜^’ and β€˜#’ characters also denote a pattern; other-
       wise 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 β€˜/’ must be matched explicitly;
       also, a β€˜.’ must be matched explicitly at the beginning of a pattern or
       after  a  β€˜/’, unless the GLOB_DOTS option is set.  No filename genera-
       tion pattern matches the files β€˜.’ or β€˜..’.  In other instances of pat-
       tern matching, the β€˜/’ and β€˜.’ 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 β€˜-’.   A  β€˜-’
              or  β€˜]’ may be matched by including it as the first character in
              the list.  There are also several named classes  of  characters,
              in the form β€˜[:name:]’ with the following meanings:  β€˜[:alnum:]’
              alphanumeric,   β€˜[:alpha:]’   alphabetic,   β€˜[:ascii:]’   7-bit,
              β€˜[:blank:]’   space   or  tab,  β€˜[:cntrl:]’  control  character,
              β€˜[:digit:]’  decimal  digit,  β€˜[:graph:]’  printable   character
              except  whitespace,  β€˜[:lower:]’  lowercase  letter, β€˜[:print:]’
              printable character,  β€˜[:punct:]’  printable  character  neither
              alphanumeric  nor  whitespace, β€˜[:space:]’ whitespace character,
              β€˜[:upper:]’ uppercase letter,  β€˜[:xdigit:]’  hexadecimal  digit.
              These  use  the  macros provided by the operating system to test
              for the given character combinations,  including  any  modifica-
              tions  due to local language settings:  see ctype(3).  Note that
              the square brackets are additional to those enclosing the  whole
              set  of characters, so to test for a single alphanumeric charac-
              ter you need β€˜[[:alnum:]]’.  Named character sets  can  be  used
              alongside other types, e.g. β€˜[[:alpha:]0-9]’.

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

       <[x]-[y]>
              Matches any number in the range x to y,  inclusive.   Either  of
              the  numbers  may be omitted to make the range open-ended; hence
              β€˜<->’ 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 β€˜<0-9>’ will
              match the first digit, and the β€˜*’ will match any others.   This
              is  a  trap  for the unwary, but is in fact an inevitable conse-
              quence of the rule that the longest possible match  always  suc-
              ceeds.   Expressions  such  as  β€˜<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 β€˜@’, β€˜*’, β€˜+’, β€˜?’ or β€˜!’
              immediately preceding the β€˜(’ 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 β€˜/’ 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  β€˜|’  character must be within parentheses, to
              avoid interpretation as a pipeline.

       ^x     (Requires EXTENDED_GLOB to be set.)  Matches anything except the
              pattern x.  This has a higher precedence than β€˜/’, so β€˜^foo/bar’
              will search directories in β€˜.’ except β€˜./foo’ for a  file  named
              β€˜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 β€˜|’, so β€˜*/*~foo/bar’ will search for
              all files in all directories in β€˜.’  and then exclude  β€˜foo/bar’
              if there was such a match.  Multiple patterns can be excluded by
              β€˜foo~bar~baz’.  In the exclusion pattern (y), β€˜/’  and  β€˜.’  are
              not treated specially the way they usually are in globbing.

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

       x##    (Requires EXTENDED_GLOB to be set.)  Matches one or more  occur-
              rences  of  the  pattern  x.  This operator has high precedence;
              β€˜12##’ is equivalent to β€˜1(2##)’, rather than β€˜(12)##’.  No more
              than two active β€˜#’ characters may appear together.

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

       @(...) Match the pattern in the parentheses.  (Like β€˜(...)’.)

       *(...) Match any number of occurrences.  (Like β€˜(...)#’.)

       +(...) Match at least one occurrence.  (Like β€˜(...)##’.)

       ?(...) Match zero or one occurrence.  (Like β€˜(|...)’.)

       !(...) Match   anything  but  the  expression  in  parentheses.   (Like
              β€˜(^(...))’.)

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

              For example,

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

              prints β€˜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 replace-
              ments 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 β€˜#’ or β€˜##’.  Only the
              last match of the parenthesis is remembered: for example, in β€˜[[
              abab =  (#b)([ab])#  ]]’,  only  the  final  β€˜b’  is  stored  in
              match[1].   Thus extra parentheses may be necessary to match the
              complete segment: for example, use  β€˜X((ab|cd)#)Y’  to  match  a
              whole  string  of either β€˜ab’ or β€˜cd’ between β€˜X’ and β€˜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.

       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  pat-
              tern, 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, print-
              ing β€˜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:  β€˜(#s)’ and β€˜(#e)’ are  the  only  valid
              forms.   The  β€˜(#s)’ flag succeeds only at the start of the test
              string, and the β€˜(#e)’ flag succeeds only at the end of the test
              string;  they  correspond  to  β€˜^’  and  β€˜$’ in standard regular
              expressions.  They are useful for matching path segments in pat-
              terns  other  than those in filename generation (where path seg-
              ments  are  in  any  case  treated  separately).   For  example,
              β€˜*((#s)|/)test((#e)|/)*’ matches a path segment β€˜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
              β€˜${array/(#s)A*Z(#e)}’ will remove only  elements  of  an  array
              which match the complete pattern β€˜A*Z’.  There are other ways of
              performing many operations of this type, however the combination
              of  the substitution operations β€˜/’ and β€˜//’ with the β€˜(#s)’ and
              β€˜(#e)’ flags provides a single simple and memorable method.

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

       q      A β€˜q’ and everything up to the closing parenthesis of the  glob-
              bing  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 β€˜(#b)(*).c(#q.)’ can be used both for
              globbing and for matching against a string.  In the former case,
              the  β€˜(#q.)’  will be treated as a glob qualifier and the β€˜(#b)’
              will not be useful, while in the latter case the β€˜(#b)’ is  use-
              ful  for  backreferences  and the β€˜(#q.)’ will be ignored.  Note
              that colon modifiers in the glob qualifiers are also not applied
              in ordinary pattern matching.

       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  charac-
       ters  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 char-
       acter).   Similarly,  errors  are counted separately for non-contiguous
       strings in the pattern, so that (ab|cd)ef is two errors from aebf.

       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 β€˜x’,  where  approximation  is
       turned off.

       Entire   path   segments   may   be   matched  approximately,  so  that
       β€˜(#a1)/foo/d/is/available/at/the/bar’ allows one error in any path seg-
       ment.   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 seg-
       ments which are known to be correct.


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

       As  a  shorthand, β€˜**/’ is equivalent to β€˜(*/)#’; note that this there-
       fore matches files in the current directory as well as  subdirectories.
       Thus:

              ls (*/)#bar

       or

              ls **/bar

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

   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 β€˜|’ or β€˜(’ characters (or β€˜~’ 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 β€˜(^x)’, can be  forced  to  be
       treated  as  part  of  the glob pattern by doubling the parentheses, in
       this case producing β€˜((^x))’.

       If the option EXTENDED_GLOB is set, a different syntax for glob  quali-
       fiers  is  available,  namely  β€˜(#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 β€˜|’, β€˜(’ or
       β€˜~’ does not negate the effect.  Note that qualifiers  will  be  recog-
       nised  in  this form even if a bare glob qualifier exists at the end of
       the pattern, for example β€˜*(#q*)(.)’ will recognise executable  regular
       files if both options are set; however, mixed syntax should probably be
       avoided for the sake of clarity.

       A qualifier may be any one of the following:

       /      directories

       F      β€˜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)

       %      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 β€˜=’, a β€˜+’, or a β€˜-’. If none of
              these characters is given, the behavior is the same as for  β€˜=’.
              The octal number describes the mode bits to be expected, if com-
              bined with a β€˜=’, the value  given  must  match  the  file-modes
              exactly,  with a β€˜+’, at least the bits in the given number must
              be set in the file-modes, and with a β€˜-’, the bits in the number
              must  not be set. Giving a β€˜?’ 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 β€˜=’.

              If the qualifier β€˜f’ is followed by any other character anything
              up  to the next matching character (β€˜[’, β€˜{’, and β€˜<’ match β€˜]’,
              β€˜}’, and β€˜>’ 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 β€˜u’, β€˜g’, β€˜o’, and β€˜a’, followed by a β€˜=’,
              a β€˜+’, or a β€˜-’, followed by a list of  any  of  the  characters
              β€˜r’,  β€˜w’,  β€˜x’, β€˜s’, and β€˜t’, or an octal digit. The first list
              of characters specify which access rights are to be checked.  If
              a  β€˜u’  is given, those for the owner of the file are used, if a
              β€˜g’ is given, those of the group are checked,  a  β€˜o’  means  to
              test  those  of  other users, and the β€˜a’ says to test all three
              groups. The β€˜=’, β€˜+’, and β€˜-’ 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: β€˜r’ for read access, β€˜w’ for
              write access, β€˜x’ for the right  to  execute  the  file  (or  to
              search a directory), β€˜s’ for the setuid and setgid bits, and β€˜t’
              for the sticky bit.

              Thus, β€˜*(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 β€˜*(f-100)’ gives all files for which the owner does
              not have execute permission,  and  β€˜*(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.

       estring
              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 sta-
              tus (usually the status of the last command).  The first charac-
              ter after the β€˜e’ will be used as a separator and anything up to
              the  next  matching separator will be taken  as the string; β€˜[’,
              β€˜{’, and β€˜<’ match β€˜]’, β€˜}’, and β€˜>’,  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.

              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
              β€˜lonely’.  Then the  expression  β€˜*(e:β€β€™reply=(${REPLY}{1,2})β€β€™:)’
              will  cause  the words β€˜lonely1 lonely2’ to be inserted into the
              command line.  Note the quotation marks.

       ddev   files on the device dev

       l[-|+]ct
              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 it is a number, if not, than the
              character after the β€˜u’ will be used  as  a  separator  and  the
              string between it and the next matching separator (β€˜[’, β€˜{’, and
              β€˜<’ match β€˜]’, β€˜}’, and β€˜>’ respectively,  any  other  character
              matches itself) will be taken as a user name, and the user ID of
              this user will be taken (e.g.  β€˜u:foo:’  or  β€˜u[foo]’  for  user
              β€˜foo’)

       gid    like uid but with group IDs or names

       a[Mwhms][-|+]n
              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 β€˜M’, β€˜w’, β€˜h’, β€˜m’ or  β€˜s’
              (e.g.  β€˜ah5’) cause the check to be performed with months (of 30
              days), weeks, hours, minutes or seconds instead of days, respec-
              tively.   For instance, β€˜echo *(ah-5)’ would echo files accessed
              within the last five hours.

       m[Mwhms][-|+]n
              like the file access qualifier, except that  it  uses  the  file
              modification time.

       c[Mwhms][-|+]n
              like  the  file  access  qualifier, except that it uses the file
              inode change time.

       L[+|-]n
              files less than n bytes (-), more than n bytes (+), or exactly n
              bytes  in  length.  If  this  flag is directly followed by a β€˜k’
              (β€˜K’), β€˜m’ (β€˜M’), or β€˜p’ (β€˜P’) (e.g. β€˜Lk-50’) the check is  per-
              formed  with  kilobytes,  megabytes,  or  blocks  (of 512 bytes)
              instead.

       ^      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

       oc     specifies how the names of the files should be sorted. If c is n
              they  are  sorted  by  name  (the  default); 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 β€˜odon’ to sort on
              names for files within the same directory.  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 β€˜*(^-oL)’ gives a list of all files sorted by
              file size in descending order, following any symbolic links.

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

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

       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
       β€˜or’ed, the qualifiers in the sublists are β€˜and’ed).  Some  qualifiers,
       however,  affect  all  matches generated, independent of the sublist in
       which they are given.  These are the qualifiers  β€˜M’,  β€˜T’,  β€˜N’,  β€˜D’,
       β€˜n’, β€˜o’, β€˜O’ and the subscripts given in brackets (β€˜[...]’).

       If  a  β€˜:’ appears in a qualifier list, the remainder of the expression
       in parenthesis is interpreted as a modifier  (see  the  section  β€˜Modi-
       fiers’  in  the  section β€˜History Expansion’).  Note that each modifier
       must be introduced by a separate β€˜:’.  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 β€˜(:..)’ even if
       no actual filename generation is performed.  Thus:

              ls *(-/)

       lists all directories and symbolic links that point to directories, 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
       β€˜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 β€˜.’ 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 builtin.pro, the shell will
       print β€˜shmiltin.shmo’.



zsh 4.2.1                       August 13, 2004                     ZSHEXPN(1)

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