zshexpn

ZSHEXPN(1)                  General Commands Manual                 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 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 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
       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.

   Overview
       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
       backslash).

       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
              `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
              `?' 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.

   Modifiers
       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 [ digits ]
              Remove a trailing pathname component, shortening the path by one
              directory level: this is the `head' of the pathname.  This works
              like `dirname'.  If the h is followed immediately (with no
              spaces or other separator) by any number of decimal digits, and
              the value of the resulting number is non-zero, that number of
              leading components is preserved instead of the final component
              being removed.  In an absolute path the leading `/' is the first
              component, so, for example, if var=/my/path/to/something, then
              ${var:h3} substitutes /my/path.  Consecutive `/'s are treated
              the same as a single `/'.  In parameter substitution, digits may
              only be used if the expression is in braces, so for example the
              short form substitution $var:h2 is treated as ${var:h}2, not as
              ${var:h2}.  No restriction applies to the use of digits in
              history substitution or globbing qualifiers.  If more components
              are requested than are present, the entire path is substituted
              (so this does not trigger a `failed modifier' error in history
              expansion).

       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.

       s/l/r[/]
              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 [ digits ]
              Remove all leading pathname components, leaving the final
              component (tail).  This works like `basename'.  Any trailing
              slashes are first removed.  Decimal digits are handled as
              described above for (h), but in this case that number of
              trailing components is preserved instead of the default 1; 0 is
              treated the same as 1.

       u      Convert the words to all uppercase.

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

       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 expansion.

       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 option:

              print -r -- *.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 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
              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.

PROCESS SUBSTITUTION
       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 completion.

       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 example,

              (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 exits.

PARAMETER EXPANSION
       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.  However, as in other shells,
       null words are elided from unquoted parameters' expansions.

       With default options, after the assignments:

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

       then $array substitutes two words, `first word' and `third word', and
       $scalar substitutes a single word `only word'.  Note that second
       element of array was elided.  Scalar parameters can be elided too if
       their value is null (empty).  To avoid elision, use quoting as follows:
       "$scalar" for scalars and "${array[@]}" or "${(@)array}" for arrays.
       (The last two forms are equivalent.)

       Parameter expansions can involve flags, as in `${(@kv)aliases}', and
       other operators, such as `${PREFIX:-"/usr/local"}'.  Parameter
       expansions can also be nested.  These topics will be introduced below.
       The full rules are complicated and are noted at the end.

       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.

       ${name}
              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:.

       ${+name}
              If name is the name of a set parameter `1' is substituted,
              otherwise `0' is substituted.

       ${name-word}
       ${name:-word}
              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.

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

       ${name=word}
       ${name:=word}
       ${name::=word}
              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.

       ${name?word}
       ${name:?word}
              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.

       ${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
              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}
              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).

       ${name:|arrayname}
              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 expression.

       ${name:*arrayname}
              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.

       ${name:^arrayname}
       ${name:^^arrayname}
              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}}"

       ${name:offset}
       ${name:offset:length}
              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.

       ${name/pattern/repl}
       ${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, 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'.

       ${#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.  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
              fashion.

       ${^spec}
              Turn on the RC_EXPAND_PARAM option for the evaluation of spec;
              if the `^' is doubled, turn it off.  When this option is set,
              array expansions of the form foo${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 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 `=' 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
              `~' 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
              expanded.

       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 PROMPT_PERCENT,
              PROMPT_SUBST and PROMPT_BANG options.

       @      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
              splitting.

              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,

                     pattern=${(q)str}
                     [[ $str = ${~pattern} ]]

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

                     pattern=${(b)str}
                     [[ $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:'.

       g:opts:
              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' interpreted.

       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 minimal 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

              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
                     duplicated values

              hide   for parameters with the `hide' flag

              hideval
                     for parameters with the `hideval' 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
              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 options)

              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,

                     sep=:
                     val=a:b:c
                     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.

       j:string:
              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.

       l:expr::string1::string2:
              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).

       r:expr::string1::string2:
              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.

       s:string:
              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 following:

                     line="one::three"
                     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}".

       Z:opts:
              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+).

       _:flags:
              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      With # or ##, search for the match that starts closest to the
              start of the string (a `substring match'). Of all matches at a
              particular position, # selects the shortest and ## the longest:

                     % str="aXbXc"
                     % echo ${(S)str#X*}
                     abXc
                     % echo ${(S)str##X*}
                     a
                     %

              With % or %%, search for the match that starts closest to the
              end of the string:

                     % str="aXbXc"
                     % echo ${(S)str%X*}
                     aXbc
                     % echo ${(S)str%%X*}
                     aXb
                     %

              (Note that % and %% don't search for the match that ends closest
              to the end of the string, as one might expect.)

              With substitution via ${.../...} or ${...//...}, specifies
              non-greedy matching, i.e. that the shortest instead of the
              longest match should be replaced:

                     % str="abab"
                     % echo ${str/*b/_}
                     _
                     % echo ${(S)str/*b/_}
                     _ab
                     %

       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
              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).

   Rules
       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
              path.)

       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 manner.

       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 value.

   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.
       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):

       "${(@)${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 `(@)' flag) the
              subscript picks the first character.

       "${${(@)foo}[1]}"
              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
              "${foo[1]}".

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

       ${(s/x/)foo}
              produces the words `a', `1 b' and `1'.

       ${(j/x/s/x/)foo}
              produces `a', `1', `b' and `1'.

       ${(s/x/)foo%%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.

COMMAND SUBSTITUTION
       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.

ARITHMETIC EXPANSION
       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'.

BRACE EXPANSION
       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.

FILENAME EXPANSION
       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 results.

       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 returned.

       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]} )) )
                  else
                    return 1
                  fi
                elif [[ $1 = n ]]; then
                  # turn the name into a directory
                  [[ $2 != (#b)p:(?*) ]] && return 1
                  typeset -ga reply
                  reply=(/home/pws/perforce/$match[1])
                elif [[ $1 = c ]]; then
                  # complete names
                  local expl
                  local -a dirs
                  dirs=(/home/pws/perforce/*(/:t))
                  dirs=(p:${^dirs})
                  _wanted dynamic-dirs expl 'dynamic directory' compadd -S\] -a dirs
                  return
                else
                  return 1
                fi
                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.

   Notes
       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.

FILENAME GENERATION
       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 ctype(3):

              [:alnum:]
                     The character is alphanumeric

              [:alpha:]
                     The character is alphabetic

              [:ascii:]
                     The character is 7-bit, i.e. is a single-byte character
                     without the top bit set.

              [:blank:]
                     The character is a blank character

              [:cntrl:]
                     The character is a control character

              [:digit:]
                     The character is a decimal digit

              [:graph:]
                     The character is a printable character other than
                     whitespace

              [:lower:]
                     The character is a lowercase letter

              [:print:]
                     The character is printable

              [:punct:]
                     The character is printable but neither alphanumeric nor
                     whitespace

              [:space:]
                     The character is whitespace

              [:upper:]
                     The character is an uppercase letter

              [:xdigit:]
                     The character is a hexadecimal digit

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

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

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

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

              [:INCOMPLETE:]
                     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.

              [:INVALID:]
                     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.

              [:WORD:]
                     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.

       <[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
              `<->' 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
              `(^(...))'.)

   Precedence
       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 referenced.

              For example,

                     foo="a_string_with_a_message"
                     if [[ $foo = (a|an)_(#b)(*) ]]; then
                       print ${foo[$mbegin[1],$mend[1]]}
                     fi

              prints `string_with_a_message'.  Note that the first set of
              parentheses 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 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 `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 -ld -- (*/)#bar

       or

              ls -ld -- **/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 -ld -- **.c

       is equivalent to

              ls -ld -- **/*.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
       significance.

       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 bit.

              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.

       estring
       +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 command).

              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 ]] }
                     NTREF=reffile
                     ls -ld -- *(+nt)

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

       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 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 `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 `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.

       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 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.

       [beg[,end]]
              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.

       Pstring
              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 -ld -- *(-/)

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

              ls -ld -- *(-@)

       lists all broken symbolic links, and

              ls -ld -- *(%W)

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

              ls -ld -- *(W,X)

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

              print -rC1 /tmp/foo*(u0^@:t)

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

              ls -ld -- *.*~(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 -rC1 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 builtin.pro, the shell will
       print `shmiltin.shmo'.



zsh 5.8                        February 14, 2020                    ZSHEXPN(1)