path: root/Doc/Zsh/expn.yo

texinode(Expansion)(Parameters)(Restricted Shell)(Top)
chapter(Expansion)
cindex(expansion)
sect(Description)
The types of expansions performed are

startlist()
list(em(History Expansion))
list(em(Alias Expansion))
list(em(Process Substitution))
list(em(Parameter Expansion))
list(em(Command Substitution))
list(em(Arithmetic Expansion))
list(em(Brace Expansion))
list(em(Filename Expansion))
list(em(Filename Generation))
endlist()

Expansion is done in the above specified order in five steps.  The
first is em(history expansion), which is only performed in
interactive shells.  The next step is em(alias expansion), which is
done right before the command line is parsed.  They are followed by
em(process substitution), em(parameter expansion), em(command
substitution), em(arithmetic expansion) and em(brace expansion)
which are performed in one step in left-to-right fashion.  After
these expansions, all unquoted occurrences of the characters `tt(\)',
`tt(')' and `tt(")' are removed, and the result is subjected to
em(filename expansion) followed by em(filename generation).

If the tt(SH_FILE_EXPANSION) option is set, the order of expansion is modified
for compatibility with bf(sh) and bf(ksh).  em(Filename expansion)
is performed immediately after em(alias expansion),
preceding the set of five expansions mentioned above.
startmenu()
menu(History Expansion)
menu(Process Substitution)
menu(Parameter Expansion)
menu(Command Substitution)
menu(Arithmetic Expansion)
menu(Brace Expansion)
menu(Filename Expansion)
menu(Filename Generation)
endmenu()
texinode(History Expansion)(Process Substitution)()(Expansion)
sect(History Expansion)
cindex(history)
cindex(history expansion)
cindex(expansion, history)
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.
Command lines are saved in the history list, the size of which
is controlled by the tt(HISTSIZE)
vindex(HISTSIZE, use of)
parameter.  The most recent command is retained in any case.
A history expansion begins with the first character of the
tt(histchars) parameter which is `tt(!)'
by default and may occur anywhere on the command line; history
expansions do not nest.  The `tt(!)' can be escaped with `tt(\)'
or can be enclosed between a pair of single quotes (tt('')) to suppress
its special meaning. Double quotes will em(not) work for this.

Input lines containing history expansions are echoed on the
terminal after being expanded, but before any other
expansions take place or the command gets executed.
startmenu()
menu(Event Designators)
menu(Word Designators)
menu(Modifiers)
endmenu()
texinode(Event Designators)(Word Designators)()(History Expansion)
subsect(Event Designators)
cindex(history event designators)
cindex(event designators, history)
An event designator is a reference to a command-line entry in
the history list.

startitem()
item(tt(!))(
Start a history expansion, except when followed by a blank, newline,
`tt(=)' or `tt(LPAR())'.
)
item(tt(!!))(
Refer to the previous command.
By itself, this expansion
repeats the previous command.
)
item(tt(!)var(n))(
Refer to command-line var(n).
)
item(tt(!-)var(n))(
Refer to the current command-line minus var(n).
)
item(tt(!)var(str))(
Refer to the most recent command starting with var(str).
)
item(tt(!?)var(str)[tt(?)])(
Refer to the most recent command containing var(str).
)
item(tt(!#))(
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 `tt(!#)' reference.
)
item(tt(!{)...tt(}))(
Insulate a history reference from adjacent characters (if necessary).
)
enditem()
texinode(Word Designators)(Modifiers)(Event Designators)(History Expansion)
subsect(Word Designators)
cindex(history word designators)
cindex(word designators, history)
A word designator indicates which word or words of a given command line will
be included in a history reference.  A `tt(:)'
separates the event specification from the word designator.
It can be omitted if the word designator begins with a
`tt(^)', `tt($)', `tt(*)', `tt(-)' or `tt(%)'.
Word designators include:

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

Note that a `tt(%)' word designator will only work when used as
`tt(!%)', `tt(!:%)' or `tt(!?)var(str)tt(?:%)',
and only when used after a tt(!?) expansion.  Anything else will result
in an error, although the error may not be the most obvious one.
texinode(Modifiers)()(Word Designators)(History Expansion)
subsect(Modifiers)
cindex(modifiers, history)
cindex(history modifiers)
After the optional word designator, you can add
a sequence of one or more of the following modifiers,
each preceded by a `tt(:)'.  These modifiers also work on the result
of em(filename generation) and em(parameter expansion), except where
noted.

startitem()
item(tt(h))(
Remove a trailing pathname component, leaving the head.
)
item(tt(r))(
Remove a trailing suffix of the form `tt(.)var(xxx)', leaving the basename.
)
item(tt(e))(
Remove all but the suffix.
)
item(tt(t))(
Remove all leading pathname components, leaving the tail.
)
item(tt(p))(
Print the new command but do not execute it.  Only works with history
expansion.
)
item(tt(q))(
Quote the substituted words, escaping further substitutions.  Works
with history expansion and parameter expansion, though in the second
case it is only useful if the resulting text is to be re-evaluated
such as by tt(eval).
)
item(tt(Q))(
Remove one level of quotes from the substituted words.
)
item(tt(x))(
Like tt(q), but break into words at each blank.
)
item(tt(l))(
Convert the words to all lowercase.
)
item(tt(u))(
Convert the words to all uppercase.
)
item(tt(f))(
(This and the following
tt(F), tt(w) and tt(W) modifier only work with parameter expansion and
filename generation.)
Repeats the immediately (without a colon) following modifier until the
resulting word doesn't change any more.
)
item(tt(F:)var(expr)tt(:))(
Like tt(f), but repeats only var(n) times if the expression
var(expr) evaluates to var(n).  Any character can be used instead of
the `tt(:)'; if `tt(LPAR())', `tt([)', or `tt({)'
is used as the opening delimiter,
the closing delimiter should be 'tt(RPAR())', `tt(])', or `tt(})',
respectively.
)
item(tt(w))(
Makes the immediately following modifier work on each word in the
string.
)
item(tt(W:)var(sep)tt(:))(
Like tt(w) but words are considered to be the parts of the string
that are separated by var(sep). Any character can be used instead of
the `tt(:)'; opening parentheses are handled specially, see above.
)
item(tt(s/)var(l)tt(/)var(r)[tt(/)])(
Substitute var(r) for var(l) as described below.
Unless preceded immediately by a tt(g), with no colon between,
the substitution is done only for the
first string that matches var(l).  For arrays and for filename
generation, this applies to each word of the expanded text.
)
item(tt(&))(
Repeat the previous tt(s) substitution.  Like tt(s), may be preceded
immediately by a tt(g).  In parameter expansion the tt(&) must appear
inside braces, and in filename generation it must be quoted with a
backslash.
)
enditem()

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

By default, a history reference with no event specification refers to the same
line as the previous history reference on that command line, unless it is the
first history reference in a command.  In that case, a history reference
with no event specification always refers to the previous command.  However,
if the option tt(CSH_JUNKIE_HISTORY) is set,
pindex(CSH_JUNKIE_HISTORY, use of)
then history reference with no
event specification will em(always) refer to the previous command.

For example, `tt(!!:1)'
will always refer to the first word of the previous command, and `tt(!!$)'
will always refer to the last word of the previous command.  And with
tt(CSH_JUNKIE_HISTORY) set, then `tt(!:1)' and `tt(!$)'
will function in the same manner as `tt(!!:1)' and `tt(!!$)',
respectively.  However, if tt(CSH_JUNKIE_HISTORY) is unset, then
`tt(!:1)' and `tt(!$)'
will refer to the first and last words respectively, of the last command
referenced on the current command line.  However, if they are the first history
reference on the command line, then they refer to the previous command.

The character sequence `tt(^)var(foo)tt(^)var(bar)' (where `tt(^)' is
actually the second charcter of the tt(histchars) parameter)
repeats the last command, replacing the string var(foo) with var(bar).
More precisely, the sequence `tt(^)var(foo)tt(^)var(bar)tt(^)' is
synonymous with `tt(!!:s)tt(^)var(foo)tt(^)var(bar)tt(^)', hence other
modifiers may follow the final `tt(^)'.

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

A less convenient but more comprehensible
form of command history support
is provided by the tt(fc) builtin.
findex(fc, use of)
texinode(Process Substitution)(Parameter Expansion)(History Expansion)(Expansion)
sect(Process Substitution)
cindex(process substitution)
cindex(substitution, process)
Each command argument of the form
`tt(<LPAR())var(list)tt(RPAR())',
`tt(>LPAR())var(list)tt(RPAR())' or
`tt(=LPAR())var(list)tt(RPAR())'
is subject to process substitution.
In the case of the tt(<) or tt(>) forms, the shell will run process
var(list) asynchronously, connected to a named pipe (FIFO).
The name of this pipe will become the argument to the command.
If the form with tt(>)
is selected then writing on this file will provide input for var(list).
If tt(<) is used, then the file passed as an argument will
be a named pipe connected to the output of the var(list) process.
For example,

nofill(tt(paste <LPAR()cut -f1) var(file1)tt(RPAR() <LPAR()cut -f3) var(file2)tt(RPAR() |
tee >LPAR())var(process1)tt(RPAR() >LPAR())var(process2)tt(RPAR() >/dev/null))

cuts fields 1 and 3 from the files var(file1) and var(file2) respectively,
pastes the results together, and sends it to the processes
var(process1) and var(process2).
Note that the file, which is passed as an argument to the command,
is a system pipe, so programs that expect to lseek (see manref(lseek)(2))
on the file will not work.
Also note that the previous example can be more compactly and
efficiently written (provided the tt(MULTIOS) option is set) as:

nofill(tt(paste <LPAR()cut -f1) var(file1)tt(RPAR() <LPAR()cut -f3) var(file2)tt(RPAR() > >LPAR())var(process1)tt(RPAR() > >LPAR())var(process2)tt(RPAR()))

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

If tt(=) is used,
then the file passed as an argument will be the name
of a temporary file containing the output of the var(list)
process.  This may be used instead of the tt(<)
form for a program that expects to lseek (see manref(lseek)(2))
on the input file.
texinode(Parameter Expansion)(Command Substitution)(Process Substitution)(Expansion)
sect(Parameter Expansion)
cindex(parameter expansion)
cindex(expansion, parameter)
The character `tt($)' is used to introduce parameter expansions.
See
ifzman(\
zmanref(zshparam)
)\
ifnzman(\
noderef(Parameters)
)\
for a description of parameters, including arrays, associative arrays,
and subscript notation to access individual array elements.

In the expansions discussed below that require a pattern, the form of
the pattern is the same as that used for filename generation;
see noderef(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 file modifiers described in
noderef(Modifiers) in noderef(History Expansion) can be
applied:  for example, tt(${i:s/foo/bar/}) performs string
substitution on the expansion of parameter tt($i).

startitem()
item(tt(${)var(name)tt(}))(
The value, if any, of the parameter var(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 var(name).  In addition, more complicated forms of substitution
usually require the braces to be present; exceptions, which only apply if
the option tt(KSH_ARRAYS) is not set, are a single subscript or any colon
modifiers appearing after the name, or any of the characters `tt(^)',
`tt(=)', `tt(~)', `tt(#)' or `tt(+)' appearing before the name, all of
which work with or without braces.

If var(name) is an array parameter, and the tt(KSH_ARRAYS) option is not
set, then the value of each
element of var(name) is substituted, one element per word.  Otherwise, the
expansion results in one word only; with tt(KSH_ARRAYS), this is the first
element of an array.  No field splitting is done on the result unless the
tt(SH_WORD_SPLIT) option is set.
)
item(tt(${PLUS())var(name)tt(}))(
If var(name) is the name of a set parameter `tt(1)' is substituted,
otherwise `tt(0)' is substituted.
)
item(tt(${)var(name)tt(:-)var(word)tt(}))(
If var(name) is set and is non-null then substitute its
value; otherwise substitute var(word). If var(name) is
missing, substitute var(word).
)
xitem(tt(${)var(name)tt(:=)var(word)tt(}))
item(tt(${)var(name)tt(::=)var(word)tt(}))(
In the first form, if var(name) is unset or is null then
set it to var(word); in the second form, unconditionally
set var(name) to var(word).  In both forms, the value of
the parameter is then substituted.
)
item(tt(${)var(name)tt(:?)var(word)tt(}))(
If var(name) is set and is non-null then substitute
its value; otherwise, print var(word) and exit from the shell.
Interactive shells instead return to the prompt.
If var(word) is omitted, then a standard message is printed.
)
item(tt(${)var(name)tt(:PLUS())var(word)tt(}))(
If var(name) is set and is non-null then substitute
var(word); otherwise substitute nothing.
)
enditem()

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

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

startitem()
xitem(tt(${)var(name)tt(#)var(pattern)tt(}))
item(tt(${)var(name)tt(##)var(pattern)tt(}))(
If the var(pattern) matches the beginning of the value of
var(name), then substitute the value of var(name) with
the matched portion deleted; otherwise, just
substitute the value of var(name).  In the first
form, the smallest matching pattern is preferred;
in the second form, the largest matching pattern is
preferred.
)
xitem(tt(${)var(name)tt(%)var(pattern)tt(}))
item(tt(${)var(name)tt(%%)var(pattern)tt(}))(
If the var(pattern) matches the end of the value of
var(name), then substitute the value of var(name) with
the matched portion deleted; otherwise, just
substitute the value of var(name).  In the first
form, the smallest matching pattern is preferred;
in the second form, the largest matching pattern is
preferred.
)
item(tt(${)var(name)tt(:#)var(pattern)tt(}))(
If the var(pattern) matches the value of var(name), then substitute
the empty string; otherwise, just substitute the value of var(name).
If var(name) is an array
the matching array elements are removed (use the `tt((M))' flag to
remove the non-matched elements).
)
xitem(tt(${)var(name)tt(/)var(pattern)tt(/)var(repl)tt(}))
item(tt(${)var(name)tt(//)var(pattern)tt(/)var(repl)tt(}))(
Replace the longest possible match of var(pattern) in the expansion of
parameter var(name) by string var(repl).  The first form
replaces just the first occurrence, the second form all occurrences.
The var(pattern) may begin with a `tt(#)', in which case the
var(pattern) must match at the start of the string, or `tt(%)', in
which case it must match at the end of the string.  The var(repl) may
be an empty string, in which case the final `tt(/)' may also be omitted.
To quote the final `tt(/)' in other cases it should be preceded by two
backslashes (i.e., a quoted backslash); this is not necessary if the
`tt(/)' occurs inside a substituted parameter.

The first `tt(/)' may be preceded by a `tt(:)', in which case the match
will only succeed if it matches the entire word.  Note also the
effect of the tt(I) and tt(S) parameter expansion flags below; however,
the flags tt(M), tt(R), tt(B), tt(E) and tt(N) are not useful.

For example,

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

Here, the `tt(~)' ensures that the text of tt($sub) is treated as a
pattern rather than a plain string.  In the first case, the longest
match for tt(t*e) is substituted and the result is `tt(spy star)',
while in the second case, the shortest matches are taken and the
result is `tt(spy spy lispy star)'.
)
item(tt(${#)var(spec)tt(}))(
If var(spec) is one of the above substitutions, substitute
the length in characters of the result instead of
the result itself.  If var(spec) is an array expression,
substitute the number of elements of the result.
Note that `tt(^)', `tt(=)', and `tt(~)', below, must appear
to the left of `tt(#)' when these forms are combined.
)
item(tt(${^)var(spec)tt(}))(
pindex(RC_EXPAND_PARAM, use of)
cindex(array expansion style, rc)
cindex(rc, array expansion style)
Turn on the tt(RC_EXPAND_PARAM) option for the
evaluation of var(spec); if the `tt(^)' is doubled, turn it off.
When this option is set, array expansions of the form
var(foo)tt(${)var(xx)tt(})var(bar),
where the parameter var(xx)
is set to tt(LPAR())var(a b c)tt(RPAR()), are substituted with
`var(fooabar foobbar foocbar)' instead of the default
`var(fooa b cbar)'.

Internally, each such expansion is converted into the
equivalent list for brace expansion.  E.g., tt(${^var}) becomes
tt({$var[1],$var[2],)...tt(}), and is processed as described in
noderef(Brace Expansion) below.
If word splitting is also in effect the
tt($var[)var(N)tt(]) may themselves be split into different list
elements.
)
item(tt(${=)var(spec)tt(}))(
pindex(SH_WORD_SPLIT, use of)
cindex(field splitting, sh style)
cindex(sh, field splitting style)
Perform word splitting using the rules for tt(SH_WORD_SPLIT) during the
evaluation of var(spec), but regardless of whether the parameter appears in
double quotes; if the `tt(=)' is doubled, turn it off.
vindex(IFS, use of)
This forces parameter expansions to be split into
separate words before substitution, using tt(IFS) as a delimiter.
This is done by default in most other shells.

Note that splitting is applied to var(word) in the assignment forms
of var(spec) em(before) the assignment to var(name) is performed.
This affects the result of array assignments with the tt(A) flag.
)
item(tt(${~)var(spec)tt(}))(
pindex(GLOB_SUBST)
Turn on the tt(GLOB_SUBST) option for the evaluation of
var(spec); if the `tt(~)' 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 `tt(=)' and `tt(!=)' operators in conditions.
)
enditem()

If a tt(${)...tt(}) type parameter expression or a
tt($LPAR())...tt(RPAR()) type command substitution is used in place of
var(name) above, it is expanded first and the result is used as if
it were the value of var(name).  Thus it is
possible to perform nested operations:  tt(${${foo#head}%tail})
substitutes the value of tt($foo) with both `tt(head)' and `tt(tail)'
deleted.  The form with tt($LPAR())...tt(RPAR()) is often useful in
combination with the flags described next; see the examples below.

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

subsect(Parameter Expansion Flags)
cindex(parameter expansion flags)
cindex(flags, parameter expansion)
cindex(substitution, parameter, 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.  Where arguments are valid, any character, or the
matching pairs `tt(LPAR())...tt(RPAR())', `tt({)...tt(})',
`tt([)...tt(])', or `tt(<)...tt(>)',  may be used
in place of the colon as delimiters.  The following flags are supported:

startitem()
item(tt(A))(
Create an array parameter with tt(${)...tt(=)...tt(}),
tt(${)...tt(:=)...tt(}) or tt(${)...tt(::=)...tt(}).
If this flag is repeated (as in tt(AA)), create an associative
array parameter.  Assignment is made before sorting or padding.
The var(name) part may be a subscripted range for ordinary
arrays; the var(word) part em(must) be converted to an array, for
example by using tt(${(AA)=)var(name)tt(=)...tt(}) to activate word
splitting, when creating an associative array.
)
item(tt(@))(
In double quotes, array elements are put into separate words.
E.g., tt("${(@)foo}") is equivalent to tt("${foo[@]}") and
tt("${(@)foo[1,2]}") is the same as tt("$foo[1]" "$foo[2]").
)
item(tt(e))(
Perform em(parameter expansion), em(command substitution) and
em(arithmetic expansion) on the result. Such expansions can be
nested but too deep recursion may have unpredictable effects.
)
item(tt(P))(
This forces the value of the parameter var(name) to be interpreted as a
further parameter name, whose value will be used where appropriate. If used
with a nested parameter or command substitution, the result of that will be
taken as a parameter name in the same way.  For example, if you have
`tt(foo=bar)' and `tt(bar=baz)', the strings tt(${(P)foo}),
tt(${(P)${foo}}), and tt${(P)$(echo bar)} will be expanded to `tt(baz)'.
)
item(tt(o))(
Sort the resulting words in ascending order.
)
item(tt(O))(
Sort the resulting words in descending order.
)
item(tt(i))(
With tt(o) or tt(O), sort case-independently.
)
item(tt(L))(
Convert all letters in the result to lower case.
)
item(tt(U))(
Convert all letters in the result to upper case.
)
item(tt(C))(
Capitalize the resulting words.  `Words' in this case refers to sequences
of alphanumeric characters separated by non-alphanumerics, em(not) to words
that result from field splitting.
)
item(tt(q))(
Quote the resulting words with backslashes.
)
item(tt(Q))(
Remove one level of quotes from the resulting words.
)
item(tt(%))(
Expand all tt(%) escapes in the resulting words in the same way as in
prompts (see noderef(Prompt Expansion)). If this flag is given twice,
full prompt expansion is done on the resulting words, depending on the 
setting of the tt(PROMPT_PERCENT), tt(PROMPT_SUBST) and
tt(PROMPT_BANG) options.
)
item(tt(X))(
With this flag parsing errors occuring with the tt(Q) flag or the
pattern matching forms such as `tt(${)var(name)tt(#)var(pattern)tt(})' 
are reported. Without the flag they are silently ignored.
)
item(tt(c))(
With tt(${#)var(name)tt(}), count the total number of characters in an array,
as if the elements were concatenated with spaces between them.
)
item(tt(w))(
With tt(${#)var(name)tt(}), count words in arrays or strings; the tt(s)
flag may be used to set a word delimiter.
)
item(tt(W))(
Similar to tt(w) with the difference that empty words between
repeated delimiters are also counted.
)
item(tt(k))(
If var(name) refers to an associative array, substitute the em(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.
)
item(tt(v))(
Used with tt(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.
)
item(tt(p))(
Recognize the same escape sequences as the tt(print) builtin
in string arguments to any of the flags described below.
)
item(tt(l:)var(expr)tt(::)var(string1)tt(::)var(string2)tt(:))(
Pad the resulting words on the left.  Each word will be truncated if
required and placed in a field var(expr) characters wide.  The space
to the left will be filled with var(string1) (concatenated as often
as needed) or spaces if var(string1) is not given.  If both
var(string1) and var(string2) are given, this string is inserted
once directly to the left of each word, before padding.
)
item(tt(r:)var(expr)tt(::)var(string1)tt(::)var(string2)tt(:))(
As tt(l), but pad the words on the right and insert var(string2)
on the right.
)
item(tt(j:)var(string)tt(:))(
Join the words of arrays together using var(string) as a separator.
pindex(SH_WORD_SPLIT, use of)
Note that this occurs before field splitting by the tt(SH_WORD_SPLIT)
option.
)
item(tt(F))(
Join the words of arrays together using newline as a separator.
This is a shorthand for `tt(pj:\n:)'.
)
item(tt(s:)var(string)tt(:))(
Force field splitting (see the option tt(SH_WORD_SPLIT)) at the
separator var(string).  Splitting only occurs in places where an
array value is valid.
)
item(tt(f))(
Split the result of the expansion to lines. This is a shorthand
for `tt(ps:\n:)'.
)
item(tt(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 (`tt(-)'). The first keyword in the string describes
the main type, it can be one of `tt(scalar)', `tt(array)', `tt(integer)',
or `tt(association)'. The other keywords describe the type in more
detail:

startitem()
item(tt(local))(
for local parameters
)
item(tt(left))(
for left justified parameters
)
item(tt(right_blanks))(
for right justified parameters with leading blanks
)
item(tt(right_zeros))(
for right justified parameters with leading zeros
)
item(tt(lower))(
for parameters whose value is converted to all lower case when it is
expanded
)
item(tt(upper))(
for parameters whose value is converted to all upper case when it is
expanded
)
item(tt(readonly))(
for readonly parameters
)
item(tt(tag))(
for tagged parameters
)
item(tt(export))(
for exported parameters
)
item(tt(unique))(
for arrays which keep only the first occurrence of duplicated values
)
enditem()
)
enditem()

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

startitem()
item(tt(S))(
Search substrings as well as beginnings or ends; with tt(#) start
from the beginning and with tt(%) start from the end of the string.
With substitution via tt(${)...tt(/)...tt(}) or
tt(${)...tt(//)...tt(}), specifies that the shortest instead of the
longest match should be replaced.
)
item(tt(I:)var(expr)tt(:))(
Search the var(expr)th match (where var(expr) evaluates to a number).
This only applies when searching for substrings, either with the tt(S)
flag, or with tt(${)...tt(/)...tt(}) (only the var(expr)th match is
substituted) or tt(${)...tt(//)...tt(}) (all matches from the
var(expr)th on are substituted).  The var(expr)th 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.
)
item(tt(M))(
Include the matched portion in the result.
)
item(tt(R))(
Include the unmatched portion in the result (the em(R)est).
)
item(tt(B))(
Include the index of the beginning of the match in the result.
)
item(tt(E))(
Include the index of the end of the match in the result.
)
item(tt(N))(
Include the length of the match in the result.
)
enditem()

subsect(Rules)

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

startitem()
item(tt(1.) em(Nested Substitution))(
If multiple nested tt(${...}) forms are present, substitution is
performed from the inside outwards.  At each level, the substitution takes
account of whether the current value is a scalar or an array, whether the
whole substitution is in double quotes, and what flags are supplied to the
current level of substitution, just as if the nested substitution were the
outermost.  The flags are not propagated up to enclosing
substitutions; the nested substitution will return either a scalar or an
array as determined by the flags, possibly adjusted for quoting.  All the
following steps take place where applicable at all levels of substitution.
Note that, unless the `tt((P))' flag is present, the flags and any subscripts
apply directly to the value of the nested substitution; for example, the
expansion tt(${${foo}}) behaves exactly the same as tt(${foo}).
)
item(tt(2.) em(Parameter Subscripting))(
If the value is a raw parameter reference with a subscript, such as
tt(${)var(var)tt([3]}), the effect of subscripting is applied directly to
the parameter.  Subscripts are evaluated left to right; subsequent
subscripts apply to the scalar or array value yielded by the previous
subscript.  Thus if tt(var) is an array, tt(${var[1][2]}) is the second
character of the first word, but tt(${var[2,4][2]}) is the entire third
word (the second word of the range of words two through four of the
original array).  Any number of subscripts may appear.
)
item(tt(3.) em(Parameter Name Replacement))(
The effect of any tt((P)) flag, which treats the value so far as a
parameter name and replaces it with the corresponding value, is applied.
)
item(tt(4.) em(Double-Quoted Joining))(
If the value after this process is an array, and the substitution
appears in double quotes, and no tt((@)) flag is present at the current
level, the words of the value are joined with the first character of the
parameter tt($IFS), by default a space, between each word (single word
arrays are not modified).  If the tt((j)) flag is present, that is used for
joining instead of tt($IFS).
)
item(tt(5.) em(Nested Subscripting))(
Any remaining subscripts (i.e. of a nested substitution) are evaluated at
this point, based on whether the value is an array or a scalar.  As with
tt(2.), multiple subscripts can appear.  Note that tt(${foo[2,4][2]}) is
thus equivalent to tt(${${foo[2,4]}[2]}) and also to
tt("${${(@)foo[2,4]}[2]}") (the nested substitution returns an array in
both cases), but not to tt("${${foo[2,4]}[2]}") (the nested substitution
returns a scalar because of the quotes).
)
item(tt(6.) em(Modifiers))(
Any modifiers, as specified by a trailing `tt(#)', `tt(%)', `tt(/)'
(possibly doubled) or by a set of modifiers of the form tt(:...) (see
noderef(Modifiers) in noderef(History Expansion)), are applied to the words
of the value at this level.
)
item(tt(7.) em(Forced Joining))(
If the `tt((j))' flag is present, or no `tt((j))' flag is present but
the string is to be split as given by rules tt(8.) or tt(9.), and joining
did not take place at step tt(4.), any words in the value are joined
together using the given string or the first character of tt($IFS) if none.
Note that the `tt((F))' flag implicitly supplies a string for joining in this
manner.
)
item(tt(8.) em(Forced Splitting))(
If one of the `tt((s))' or `tt((f))' flags are present, or the `tt(=)'
specifier was present (e.g. tt(${=)var(var)tt(})), the word is split on
occurrences of the specified string, or (for tt(=) with neither of the two
flags present) any of the characters in tt($IFS).
)
item(tt(9.) em(Shell Word Splitting))(
If no `tt((s))', `tt((f))' or `tt(=)' was given, but the word is not
quoted and the option tt(SH_WORD_SPLIT) is set, the word is split on
occurrences of any of the characters in tt($IFS).  Note this step, too,
take place at all levels of a nested substitution.
)
item(tt(10.) em(Re-Evaluation))(
Any `tt((e))' flag is applied to the value, forcing it to be re-examined
for new parameter substitutions, but also for command and arithmetic
substitutions.
)
item(tt(11.) em(Padding))(
Any padding of the value by the `tt(LPAR()l.)var(fill)tt(.RPAR())' or
`tt(LPAR()r.)var(fill)tt(.RPAR())' flags is applied.
)
enditem()

subsect(Examples)
The flag tt(f) is useful to split a double-quoted substitution line by
line.  For example, tt(${(f)"$LPAR()<)var(file)tt(RPAR()"})
substitutes the contents of var(file) divided so that each line is
an element of the resulting array.  Compare this with the effect of
tt($)tt(LPAR()<)var(file)tt(RPAR()) 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 tt($foo) contains the array tt(LPAR()bar baz)tt(RPAR()):

startitem()
item(tt("${(@)${foo}[1]}"))(
This produces the result tt(b).  First, the inner substitution
tt("${foo}"), which has no array (tt(@)) flag, produces a single word
result tt("bar baz").  The outer substitution tt("${(@)...[1]}") detects
that this is a scalar, so that (despite the `tt((@))' flag) the subscript
picks the first character. 
)
item(tt("${${(@)foo}[1]}"))(
The produces the result `tt(bar)'.  In this case, the inner substitution
tt("${(@)foo}") produces the array `tt(LPAR()bar baz)tt(RPAR())'.  The outer
substitution tt("${...[1]}") detects that this is an array and picks the
first word.  This is similar to the simple case tt("${foo[1]}").
)
enditem()

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

startitem()
item(tt(${(s/x/)foo}))(
produces the words `tt(a)', `tt(1 b)' and `tt(1)'.
)
item(tt(${(j/x/s/x/)foo}))(
produces `tt(a)', `tt(1)', `tt(b)' and `tt(1)'.
)
item(tt(${(s/x/)foo%%1*}))(
produces `tt(a)' and `tt( b)' (note the extra space).  As substitution
occurs before either joining or splitting, the operation  first generates
the modified array tt(LPAR()ax bx)tt(RPAR()), which is joined to give
tt("ax bx"), and then split to give `tt(a)', `tt( b)' and `'.  The final
empty string will then be elided, as it is not in double quotes.
)
enditem()

texinode(Command Substitution)(Arithmetic Expansion)(Parameter Expansion)(Expansion)
sect(Command Substitution)
cindex(command substitution)
cindex(substitution, command)
A command enclosed in parentheses preceded by a dollar sign, like
`tt($LPAR())...tt(RPAR())', or quoted with grave 
accents, like `tt(`)...tt(`)', is replaced with its standard output, with
any trailing newlines deleted.
If the substitution is not enclosed in double quotes, the
output is broken into words using the tt(IFS) parameter.
vindex(IFS, use of)
The substitution `tt($LPAR()cat) var(foo)tt(RPAR())' may be replaced
by the equivalent but faster `tt($LPAR()<)var(foo)tt(RPAR())'.
In either case, if the option tt(GLOB_SUBST) is set,
the output is eligible for filename generation.
texinode(Arithmetic Expansion)(Brace Expansion)(Command Substitution)(Expansion)
sect(Arithmetic Expansion)
cindex(arithmetic expansion)
cindex(expansion, arithmetic)
A string of the form `tt($[)var(exp)tt(])' or
`tt($LPAR()LPAR())var(exp)tt(RPAR()RPAR())' is substituted
with the value of the arithmetic expression var(exp).  var(exp) is
subjected to em(parameter expansion), em(command substitution)
and em(arithmetic expansion) before it is evaluated.
See noderef(Arithmetic Evaluation).
texinode(Brace Expansion)(Filename Expansion)(Arithmetic Expansion)(Expansion)
sect(Brace Expansion)
cindex(brace expansion)
cindex(expansion, brace)
A string of the form
`var(foo)tt({)var(xx)tt(,)var(yy)tt(,)var(zz)tt(})var(bar)'
is expanded to the individual words
`var(fooxxbar)', `var(fooyybar)' and `var(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 `tt({)var(n1)tt(..)var(n2)tt(})',
where var(n1) and var(n2) are integers,
is expanded to every number between
var(n1) and var(n2) inclusive.  If either number begins with a
zero, all the resulting numbers will be padded with leading zeroes to
that minimum width.  If the numbers are in decreasing order the
resulting sequence will also be in decreasing order.

If a brace expression matches none of the above forms, it is left
unchanged, unless the tt(BRACE_CCL) option is set.
pindex(BRACE_CCL, use of)
In that case, it is expanded to a sorted list of the individual
characters between the braces, in the manner of a search set.
`tt(-)' is treated specially as in a search set, but `tt(^)' or `tt(!)' as
the first character is treated normally.

Note that brace expansion is not part of filename generation (globbing); an
expression such as tt(*/{foo,bar}) is split into two separate words
tt(*/foo) and tt(*/bar) before filename generation takes place.  In
particular, note that this is liable to produce a `no match' error if
em(either) of the two expressions does not match; this is to be contrasted
with tt(*/(foo|bar)), which is treated as a single pattern but otherwise
has similar effects.
texinode(Filename Expansion)(Filename Generation)(Brace Expansion)(Expansion)
sect(Filename Expansion)
cindex(filename expansion)
cindex(expansion, filename)
Each word is checked to see if it begins with an unquoted `tt(~)'.
If it does, then the word up to a `tt(/)',
or the end of the word if there is no `tt(/)',
is checked to see if it can be substituted in one of the ways
described here.  If so, then the `tt(~)' and the checked portion are
replaced with the appropriate substitute value.

A `tt(~)' by itself is replaced by the value of tt($HOME).
A `tt(~)' followed by a `tt(PLUS())' or a `tt(-)' is replaced by the value of
tt($PWD) or tt($OLDPWD), respectively.

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

cindex(directories, named)
cindex(named directories)
A `tt(~)' followed by anything not already covered is looked up as a
named directory, and replaced by the value of that named directory if found.
Named directories are typically home directories for users on the system.
They may also be defined if the text after the `tt(~)' is the name
of a string shell parameter whose value begins with a `tt(/)'.
It is also possible to define directory names using the tt(-d) option to the
tt(hash) builtin.

In certain circumstances (in prompts, for instance), when the shell
prints a path, the path is checked to see if it has a named
directory as its prefix.  If so, then the prefix portion
is replaced with a `tt(~)' followed by the name of the directory.
The shortest way of referring to the directory is used,
with ties broken in favour of using a named directory,
except when the directory is tt(/) itself.  The parameters tt($PWD) and
tt($OLDPWD) are never abbreviated in this fashion.

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

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

If the option tt(MAGIC_EQUAL_SUBST) is set, any unquoted shell
argument in the form `var(identifier)tt(=)var(expression)' becomes eligible
for file expansion as described in the previous paragraph.  Quoting the
first `tt(=)' also inhibits this.
texinode(Filename Generation)()(Filename Expansion)(Expansion)
sect(Filename Generation)
cindex(filename generation)
cindex(globbing)
If a word contains an unquoted instance of one of the characters
`tt(*)', `tt(LPAR())', `tt(|)', `tt(<)', `tt([)', or `tt(?)', it is regarded
as a pattern for filename generation, unless the tt(GLOB) option is unset.
pindex(GLOB, use of)
If the tt(EXTENDED_GLOB) option is set,
pindex(EXTENDED_GLOB, use of)
the `tt(^)' and `tt(#)' 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 tt(NULL_GLOB) option is set,
pindex(NULL_GLOB, use of)
in which case the word is deleted; or unless the tt(NOMATCH)
option is unset, in which case the word is left unchanged.
pindex(NOMATCH, use of)

In filename generation,
the character `tt(/)' must be matched explicitly;
also, a `tt(.)' must be matched
explicitly at the beginning of a pattern or after a `tt(/)', unless the
tt(GLOB_DOTS) option is set.
pindex(GLOB_DOTS, use of)
No filename generation pattern
matches the files `tt(.)' or `tt(..)'.  In other instances of pattern
matching, the `tt(/)' and `tt(.)' are not treated specially.
subsect(Glob Operators)
startitem()
item(tt(*))(
Matches any string, including the null string.
)
item(tt(?))(
Matches any character.
)
item(tt([)...tt(]))(
Matches any of the enclosed characters.  Ranges of characters
can be specified by separating two characters by a `tt(-)'.
A `tt(-)' or `tt(])' may be matched by including it as the
first character in the list.
There are also several named classes of characters, in the form
`tt([:)var(name)tt(:])' with the following meanings:  `tt([:alnum:])'
alphanumeric, `tt([:alpha:])' alphabetic,
`tt([:blank:])' space or tab,
`tt([:cntrl:])' control character, `tt([:digit:])' decimal
digit, `tt([:graph:])' printable character except whitespace,
`tt([:lower:])' lowercase letter, `tt([:print:])' printable character,
`tt([:punct:])' printable character neither alphanumeric nor whitespace,
`tt([:space:])' whitespace character, `tt([:upper:])' uppercase letter, 
`tt([:xdigit:])' hexadecimal digit.  These use the macros provided by
the operating system to test for the given character combinations,
including any modifications due to local language settings:  see
manref(ctype)(3).  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 `tt([[:alnum:]])'.  Named
character sets can be used alongside other types,
e.g. `tt([[:alpha:]0-9])'.
)
xitem(tt([^)...tt(]))
item(tt([!)...tt(]))(
Like tt([)...tt(]), except that it matches any character which is
not in the given set.
)
item(tt(<)[var(x)]tt(-)[var(y)]tt(>))(
Matches any number in the range var(x) to var(y), inclusive.
Either of the numbers may be omitted to make the range open-ended;
hence `tt(<->)' matches any number.  To match individual digits, the
tt([)...tt(]) form is more efficient.
)
item(tt(LPAR())...tt(RPAR()))(
Matches the enclosed pattern.  This is used for grouping.
If the tt(KSH_GLOB) option is set, then a
`tt(@)', `tt(*)', `tt(+)', `tt(?)' or `tt(!)' immediately preceding
the `tt(LPAR())' is treated specially, as detailed below. The option
tt(SH_GLOB) prevents bare parentheses from being used in this way, though
the tt(KSH_GLOB) option is still available.

Note that grouping cannot extend over multiple directories: it is an error
to have a `tt(/)' within a group (this only applies for patterns used in
filename generation).  There is one exception:  a group of the form
tt(LPAR())var(pat)tt(/RPAR()#) appearing as a complete path segment can
match a sequence of directories.  For example, tt(foo/(a*/)#bar) matches
tt(foo/bar), tt(foo/any/bar), tt(foo/any/anyother/bar), and so on.
)
item(var(x)tt(|)var(y))(
Matches either var(x) or var(y).
This operator has lower precedence than any other.
The `tt(|)' character
must be within parentheses, to avoid interpretation as a pipeline.
)
item(tt(^)var(x))(
(Requires tt(EXTENDED_GLOB) to be set.)
Matches anything except the pattern var(x).
This has a higher precedence than `tt(/)', so `tt(^foo/bar)'
will search directories in `tt(.)' except `tt(./foo)'
for a file named `tt(bar)'.
)
item(var(x)tt(~)var(y))(
(Requires tt(EXTENDED_GLOB) to be set.)
Match anything that matches the pattern var(x) but does not match var(y).
This has lower precedence than any operator except `tt(|)', so
`tt(*/*~foo/bar)' will search for all files in all directories in `tt(.)'
and then exclude `tt(foo/bar)' if there was such a match.
Multiple patterns can be excluded by
`var(foo)tt(~)var(bar)tt(~)var(baz)'.
In the exclusion pattern (var(y)), `tt(/)' and `tt(.)' are not treated
specially the way they usually are in globbing.
)
item(var(x)tt(#))(
(Requires tt(EXTENDED_GLOB) to be set.)
Matches zero or more occurrences of the pattern var(x).
This operator has high precedence; `tt(12#)' is equivalent to `tt(1(2#))',
rather than `tt((12)#)'.  It is an error for an unquoted `tt(#)' to follow
something which cannot be repeated; this includes an empty string, a
pattern already followed by `tt(##)', or parentheses when part of a
tt(KSH_GLOB) pattern (for example, `tt(!LPAR())var(foo)tt(RPAR()#)' is
invalid and must be replaced by
`tt(*LPAR()!LPAR())var(foo)tt(RPAR()RPAR())').
)
item(var(x)tt(##))(
(Requires tt(EXTENDED_GLOB) to be set.)
Matches one or more occurrences of the pattern var(x).
This operator has high precedence; `tt(12##)' is equivalent to `tt(1(2##))',
rather than `tt((12)##)'.  No more than two active `tt(#)' characters may
appear together.
)
enditem()
subsect(ksh-like Glob Operators)
pindex(KSH_GLOB, use of)
If the tt(KSH_GLOB) option is set, the effects of parentheses can be
modified by a preceding `tt(@)', `tt(*)', `tt(+)', `tt(?)' or `tt(!)'.
This character need not be unquoted to have special effects,
but the `tt(LPAR())' must be.

startitem()
item(tt(@LPAR())...tt(RPAR()))(
Match the pattern in the parentheses.  (Like `tt(LPAR())...tt(RPAR())'.)
)
item(tt(*LPAR())...tt(RPAR()))(
Match any number of occurrences.  (Like `tt(LPAR())...tt(RPAR()#)'.)
)
item(tt(PLUS()LPAR())...tt(RPAR()))(
Match at least one occurrence.  (Like `tt(LPAR())...tt(RPAR()##)'.)
)
item(tt(?LPAR())...tt(RPAR()))(
Match zero or one occurrence.  (Like `tt(LPAR()|)...tt(RPAR())'.)
)
item(tt(!LPAR())...tt(RPAR()))(
Match anything but the expression in parentheses.
(Like `tt(LPAR()^LPAR())...tt(RPAR()RPAR())'.)
)
enditem()
subsect(Precedence)
cindex(precedence of glob operators)
The precedence of the operators given above is (highest) `tt(^)', `tt(/)',
`tt(~)', `tt(|)' (lowest); the
remaining operators are simply treated from left to right as part of a
string, with `tt(#)' and `tt(##)' applying to the shortest possible
preceeding unit (i.e. a character, `tt(?)', `tt([)...tt(])',
`tt(<)...tt(>)', or a parenthesised expression).  As mentioned
above, a `tt(/)' used as a directory separator may not appear inside
parentheses, while a `tt(|)' must do so; in patterns used in other contexts
than filename generation (for example, in tt(case) statements and tests
within `tt([[)...tt(]])'), a `tt(/)' is not special; and `tt(/)' is also
not special after a `tt(~)' appearing outside parentheses in a filename
pattern.
subsect(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 tt(EXTENDED_GLOB) option. All take the form
tt(LPAR()#)var(X)tt(RPAR()) where var(X) may have one of the following
forms:

startitem()
item(i)(
Case insensitive:  upper or lower case characters in the pattern match
upper or lower case characters.
)
item(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.
)
item(I)(
Case sensitive:  locally negates the effect of tt(i) or tt(l) from
that point on.
)
item(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 tt($match), the indices of the beginning of the matched
parentheses in the array tt($mbegin), and the indices of the end in the array
tt($mend), with the first element of each array corresponding to the first
parenthesised group, and so on.  These arrays are not otherwise special to
the shell.  The indices use the same convention as does parameter
substitution, so that elements of tt($mend) and tt($mbegin) may be used in
subscripts; the tt(KSH_ARRAYS) option is respected.  Sets of globbing flags
are not considered parenthesised groups.

For example,

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

prints `tt(string with a)'.  Note that the first parenthesis is before the
tt((#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 tt(${)var(array)tt(#)var(pattern)tt(}), or a global substitution, such
as tt(${)var(param)tt(//)var(pat)tt(/)var(repl)tt(}), 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 tt(m) flag below.

If the match fails none of the parameters is altered, so in some cases it
may be necessary to initialise them beforehand.

Pattern matching with backreferences is slightly slower than without.
)
item(B)(
Deactivate backreferences, negating the effect of the tt(b) flag from that
point on.
)
item(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 tt($MATCH),  tt($MBEGIN) and tt($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,

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
`tt(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.
)
item(M)(
Deactivate the tt(m) flag, hence no references to match data will be
created.
)
item(tt(a)var(num))(
Approximate matching: var(num) errors are allowed in the string matched by
the pattern.  The rules for this are described in the next subsection.
)
enditem()

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

When using the ksh syntax for grouping both tt(KSH_GLOB) and
tt(EXTENDED_GLOB) must be set and the left parenthesis should be
preceded by tt(@).  Note also that the flags do not affect letters
inside tt([...]) groups, in other words tt(LPAR()#i)tt(RPAR()[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
tt(LPAR()#i)tt(RPAR()/foo/bar/...) is potentially slow.

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

startitem()
item(1.)(
Different characters, as in tt(fooxbar) and tt(fooybar).
)
item(2.)(
Transposition of characters, as in tt(banana) and tt(abnana).
)
item(3.)(
A character missing in the target string, as with the pattern tt(road) and
target string tt(rod).
)
item(4.)(
An extra character appearing in the target string, as with tt(stove)
and tt(strove).
)
enditem()

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

Non-literal parts of the pattern must match exactly, including characters
in character ranges: hence tt(LPAR()#a1)tt(RPAR()???)  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 tt(?) must match.  Other characters
which must match exactly are initial dots in filenames (unless the
tt(GLOB_DOTS) option is set), and all slashes in filenames, so that
tt(a/bc) is two errors from tt(ab/c) (the slash cannot be transposed with
another character).  Similarly, errors are counted separately for
non-contiguous strings in the pattern, so that tt(LPAR()ab|cd)tt(RPAR()ef)
is two errors from tt(aebf).

When using exclusion via the tt(~) operator, approximate matching is
treated entirely separately for the excluded part and must be activated
separately.  Thus, tt(LPAR()#a1)tt(RPAR()README~READ_ME) matches
tt(READ.ME) but not tt(READ_ME), as the trailing tt(READ_ME) is matched
without approximation.  However,
tt(LPAR()#a1)tt(RPAR()README~LPAR()#a1)tt(RPAR()READ_ME)
does not match any pattern of the form tt(READ)var(?)tt(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,
tt(LPAR()#a1)tt(RPAR()cat)tt(LPAR()LPAR()#a0)tt(RPAR()dog)tt(RPAR()fox)
allows one error in total, which may not occur in the tt(dog) section, and
the pattern
tt(LPAR()#a1)tt(RPAR()cat)tt(LPAR()#a0)tt(RPAR()dog)tt(LPAR()#a1)tt(RPAR()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,
tt((#a1)abc(#a0)xyz) will not match tt(abcdxyz), because the error occurs
at the `tt(x)', where approximation is turned off.

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

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

example(ls (*/)#bar)

or

example(ls **/bar)

does a recursive directory search for files named `tt(bar)' (potentially
including the file `tt(bar)' in the current directory), not following
symbolic links.  To follow links, use `tt(***/)'.  Neither of these can be
combined with other forms of globbing within the same filename segment; in
that case, the `tt(*)' operators revert to their usual effect.
subsect(Glob Qualifiers)
cindex(globbing, qualifiers)
cindex(qualifiers, globbing)
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.

pindex(BARE_GLOB_QUAL, use of)
If the option tt(BARE_GLOB_QUAL) is set, then a trailing set of parentheses
containing no `tt(|)' or `tt(LPAR())' characters (or `tt(~)' 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 `tt((^x))', can be forced to be treated as part of
the glob pattern by doubling the parentheses, for example `tt(((^x)))'.

A qualifier may be any one of the following:

startitem()
item(tt(/))(
directories
)
item(tt(.))(
plain files
)
item(tt(@))(
symbolic links
)
item(tt(=))(
sockets
)
item(tt(p))(
named pipes (FIFOs)
)
item(tt(*))(
executable plain files (0100)
)
item(tt(%))(
device files (character or block special)
)
item(tt(%b))(
block special files
)
item(tt(%c))(
character special files
)
item(tt(r))(
owner-readable files (0400)
)
item(tt(w))(
owner-writable files (0200)
)
item(tt(x))(
owner-executable files (0100)
)
item(tt(A))(
group-readable files (0040)
)
item(tt(I))(
group-writable files (0020)
)
item(tt(E))(
group-executable files (0010)
)
item(tt(R))(
world-readable files (0004)
)
item(tt(W))(
world-writable files (0002)
)
item(tt(X))(
world-executable files (0001)
)
item(tt(s))(
setuid files (04000)
)
item(tt(S))(
setgid files (02000)
)
item(tt(t))(
files with the sticky bit (01000)
)
item(tt(f)var(spec))(
files with access rights matching var(spec). This var(spec) may be a
octal number optionally preceded by a `tt(=)', a `tt(PLUS())', or a
`tt(-)'. If none of these characters is given, the behavior is the
same as for `tt(=)'. The octal number describes the mode bits to be
expected, if combined with a `tt(=)', the value given must match the
file-modes exactly, with a `tt(PLUS())', at least the bits in the
given number must be set in the file-modes, and with a `tt(-)', the
bits in the number must not be set. Giving a `tt(?)' 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 `tt(=)'.

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

Thus, `tt(*(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
`tt(*(f-100))' gives all files for which the owner does not have
execute permission, and `tt(*(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.
)
item(tt(e)var(string))(
The var(string) will be executed and the return value determines if the
filename should be included in the list (if it is zero) or not (if it
is non-zero). The first character after the `tt(e)' will be used as a
separator and anything up to the next matching separator will be taken 
as the var(string) (`tt([)', `tt({)', and `tt(<)' match `tt(])',
`tt(})', and `tt(>)' respectively, any other character matches
itself). Note that expansions have to be quoted in the var(string) to
prevent them from being expanded before globbing is done.

During the execution of var(string) the parameter tt(REPLY) is set to
the filename currently being tested. It may also be set to any string
to make this string be inserted into the list instead of the original
filename. Also, the parameter tt(reply) may be set to an array or a
string and if it is, these strings will be inserted instead of the
value of the tt(REPLY) parameter. For security reasons, tt(reply)
will be unset by the shell before the var(string) is executed.
)
item(tt(d)var(dev))(
files on the device var(dev)
)
item(tt(l)[tt(-)|tt(PLUS())]var(ct))(
files having a link count less than var(ct) (tt(-)), greater than
var(ct) (tt(PLUS())), or is equal to var(ct)
)
item(tt(U))(
files owned by the effective user ID
)
item(tt(G))(
files owned by the effective group ID
)
item(tt(u)var(id))(
files owned by user ID var(id) if it is a number, if not, than the
character after the `tt(u)' will be used as a separator and the string
between it and the next matching separator
(`tt([)', `tt({)', and `tt(<)'
match `tt(])', `tt(})', and `tt(>)' respectively,
any other character matches
itself) will be taken as a user name, and the user ID of this user will
be taken (e.g. `tt(u:foo:)' or `tt(u[foo])' for user `tt(foo)')
)
item(tt(g)var(id))(
like tt(u)var(id) but with group IDs or names
)
item(tt(a)[tt(Mwhms)][tt(-)|tt(PLUS())]var(n))(
files accessed exactly var(n) days ago.  Files accessed within the last
var(n) days are selected using a negative value for var(n) (tt(-)var(n)).
Files accessed more than var(n) days ago are selected by a positive var(n)
value (tt(PLUS())var(n)).  Optional unit specifiers `tt(M)', `tt(w)',
`tt(h)', `tt(m)' or `tt(s)' (e.g. `tt(ah5)') cause the check to be
performed with months (of 30 days), weeks, hours, minutes or seconds
instead of days, respectively.  For instance, `tt(echo *(ah-5))' would
echo files accessed within the last five hours.
)
item(tt(m)[tt(Mwhms)][tt(-)|tt(PLUS())]var(n))(
like the file access qualifier, except that it uses the file modification
time.
)
item(tt(c)[tt(Mwhms)][tt(-)|tt(PLUS())]var(n))(
like the file access qualifier, except that it uses the file inode change
time.
)
item(tt(L)[tt(PLUS())|tt(-)]var(n))(
files less than var(n) bytes (tt(-)), more than var(n) bytes (tt(PLUS())), or
exactly var(n) bytes in length. If this flag is directly followed by a `tt(k)'
(`tt(K)'), `tt(m)' (`tt(M)'), or `tt(p)' (`tt(P)') (e.g. `tt(Lk-50)')
the check is performed with kilobytes, megabytes, or blocks (of 512 bytes)
instead.
)
item(tt(^))(
negates all qualifiers following it
)
item(tt(-))(
toggles between making the qualifiers work on symbolic links (the
default) and the files they point to
)
item(tt(M))(
sets the tt(MARK_DIRS) option for the current pattern
pindex(MARK_DIRS, setting in pattern)
)
item(tt(T))(
appends a trailing qualifier mark to the filenames, analogous to the
tt(LIST_TYPES) option, for the current pattern (overrides tt(M))
)
item(tt(N))(
sets the tt(NULL_GLOB) option for the current pattern
pindex(NULL_GLOB, setting in pattern)
)
item(tt(D))(
sets the tt(GLOB_DOTS) option for the current pattern
pindex(GLOB_DOTS, setting in pattern)
)
item(tt(o)var(c))(
specifies how the names of the files should be sorted. If var(c) is
tt(n) they are sorted by name (the default), if it is tt(L) they
are sorted depending on the size (length) of the files, if tt(l) 
they are sorted by the number of links, and if tt(a), tt(m), and tt(c)
they are sorted by the time of the last access, modification, or
inode change respectively. Note that tt(a), tt(m), and tt(c) compare
the age against the current time, hence the first name in the list is the 
the youngest file. Also note that the modifiers tt(^) and tt(-) are 
used, so `tt(*(^-oL))' gives a list of all files sorted by file size in 
descending order, following any symbolic links.
)
item(tt(O)var(c))(
like `tt(o)', but sorts in descending order; i.e. `tt(*(^oc))' is the
same as `tt(*(Oc))' and `tt(*(^Oc))' is the same as `tt(*(oc))'
)
item(tt([)var(beg)[tt(,)var(end)]tt(]))(
specifies which of the matched filenames should be included in the
returned list. The syntax is the same as for array
subscripts. var(beg) and the optional var(end) may be mathematical
expressions. As in parameter subscripting they may be negative to make 
them count from the last match backward. E.g.: `tt(*(-OL[1,3]))'
gives a list of the names of the three largest files.
)
enditem()

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).

If a `tt(:)' appears in a qualifier list, the remainder of the expression in
parenthesis is interpreted as a modifier (see noderef(Modifiers)
in noderef(History Expansion)).  Note that
each modifier must be introduced by a separate `tt(:)'.  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
`tt((:..))' even if no actual filename generation is performed.
Thus:

example(ls *(-/))

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

example(ls *(%W))

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

example(ls *(W,X))

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

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

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

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

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