<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
**Table of Contents**  *generated with [DocToc](https://github.com/thlorenz/doctoc)*

- [14 Expansion](#14-expansion)
  - [14.1 History Expansion](#141-history-expansion)
    - [14.1.1 Overview](#1411-overview)
    - [14.1.2 Event Designators](#1412-event-designators)
    - [14.1.3 Word Designators](#1413-word-designators)
    - [14.1.4 Modifiers](#1414-modifiers)
  - [14.2 Process Substitution](#142-process-substitution)
  - [14.3 Parameter Expansion](#143-parameter-expansion)
    - [14.3.1 Parameter Expansion Flags](#1431-parameter-expansion-flags)
- [](#)
    - [14.3.2 Rules](#1432-rules)
    - [14.3.3 Examples](#1433-examples)
  - [14.4 Command Substitution](#144-command-substitution)
  - [14.5 Arithmetic Expansion](#145-arithmetic-expansion)
  - [14.6 Brace Expansion](#146-brace-expansion)
  - [14.7 Filename Expansion](#147-filename-expansion)
    - [14.7.1 Dynamic named directories](#1471-dynamic-named-directories)
    - [14.7.2 Static named directories](#1472-static-named-directories)
    - [14.7.3 ‘=’ expansion](#1473--expansion)
    - [14.7.4 Notes](#1474-notes)
  - [14.8 Filename Generation](#148-filename-generation)
    - [14.8.1 Glob Operators](#1481-glob-operators)
    - [14.8.2 ksh-like Glob Operators](#1482-ksh-like-glob-operators)
    - [14.8.3 Precedence](#1483-precedence)
    - [14.8.4 Globbing Flags](#1484-globbing-flags)
    - [14.8.5 Approximate Matching](#1485-approximate-matching)
    - [14.8.6 Recursive Globbing](#1486-recursive-globbing)
    - [14.8.7 Glob Qualifiers](#1487-glob-qualifiers)

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<span id="Expansion"></span> <span id="Expansion-1"></span>

# 14 Expansion

<span id="index-expansion"></span>

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 in [Aliasing](Shell-Grammar.html#Aliasing).

*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.

<span id="index-globbing"></span>

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

The following sections explain the types of expansion in detail.

------------------------------------------------------------------------

<span id="History-Expansion"></span> <span
id="History-Expansion-1"></span>

## 14.1 History Expansion

<span id="index-history"></span> <span
id="index-history-expansion"></span> <span
id="index-expansion_002c-history"></span>

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.

<span id="index-HISTSIZE_002c-use-of"></span>

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 [Prompt
Expansion](Prompt-Expansion.html#Prompt-Expansion)) is the number that
is to be assigned to the *next* command.

------------------------------------------------------------------------

<span id="Overview"></span> <span id="Overview-1"></span>

### 14.1.1 Overview

<span id="index-histchars_002c-use-of-1"></span>

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 ([Event
Designators](#Event-Designators)) and then an optional word designator
([Word Designators](#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. <span id="index-CSH_005fJUNKIE_005fHISTORY_002c-use-of"></span>
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 [Modifiers](#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
[Shell Grammar](Shell-Grammar.html#Shell-Grammar)) is fully parsed. The
‘!"’ is removed from the input, and any subsequent ‘!’ characters have
no special significance.

<span id="index-fc_002c-use-of"></span>

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

------------------------------------------------------------------------

<span id="Event-Designators"></span> <span
id="Event-Designators-1"></span>

### 14.1.2 Event Designators

<span id="index-history-event-designators"></span> <span
id="index-event-designators_002c-history"></span>

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 ([Word
Designators](#Word-Designators)), this forms a history reference with no
event designator ([Overview](#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).

------------------------------------------------------------------------

<span id="Word-Designators"></span> <span
id="Word-Designators-1"></span>

### 14.1.3 Word Designators

<span id="index-history-word-designators"></span> <span
id="index-word-designators_002c-history"></span>

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 `n`th 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.

------------------------------------------------------------------------

<span id="Modifiers"></span> <span id="Modifiers-1"></span>

### 14.1.4 Modifiers

<span id="index-modifiers"></span> <span
id="index-colon-modifiers"></span> <span
id="index-history-modifiers"></span> <span
id="index-globbing-modifiers"></span> <span
id="index-parameter-modifiers"></span>

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, will refer to the same directory entry as the
input filename, and none of its components will be symbolic links or
equal to ‘.’ or ‘..’.

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 [Filename Generation](#Filename-Generation).
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:

<div class="example">

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

</div>

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.

------------------------------------------------------------------------

<span id="Process-Substitution"></span> <span
id="Process-Substitution-1"></span>

## 14.2 Process Substitution

<span id="index-process-substitution"></span> <span
id="index-substitution_002c-process"></span>

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,

<div class="example">

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

</div>

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:

<div class="example">

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

</div>

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
[Redirection](Redirection.html#Redirection). Hence in a simplified
version of the example above:

<div class="example">

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

</div>

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

<div class="example">

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

</div>

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,

<div class="example">

```zsh
(mycmd =(myoutput)) &!
```

</div>

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:

<div class="example">

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

</div>

outputs something resembling the following

<div class="example">

```zsh
File /tmp/zsh6nU0kS:
This be the verse
```

</div>

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

------------------------------------------------------------------------

<span id="Parameter-Expansion"></span> <span
id="Parameter-Expansion-1"></span>

## 14.3 Parameter Expansion

<span id="index-parameter-expansion"></span> <span
id="index-expansion_002c-parameter"></span>

The character ‘$’ is used to introduce parameter expansions. See
[Parameters](Parameters.html#Parameters) 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:

<div class="example">

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

</div>

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
[Filename Generation](#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 [Modifiers](#Modifiers) in [History
Expansion](#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,

<div class="example">

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

</div>

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.

<div class="example">

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

</div>

${`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

<div class="example">

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

</div>

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,

<div class="example">

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

</div>

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`}  
${^^`spec`}  
<span id="index-RC_005fEXPAND_005fPARAM_002c-toggle"></span> <span
id="index-array-expansion-style_002c-rc"></span> <span
id="index-rc_002c-array-expansion-style"></span>

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 [Brace Expansion](#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`}  
${==`spec`}  
<span id="index-SH_005fWORD_005fSPLIT_002c-toggle"></span> <span
id="index-field-splitting_002c-sh-style_002c-parameter"></span> <span
id="index-sh_002c-field-splitting-style_002c-parameter"></span>

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. <span
id="index-IFS_002c-use-of"></span> 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`}  
${\~\~`spec`}  
<span id="index-GLOB_005fSUBST_002c-toggle"></span>

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](Parameters.html#Array-Parameters).

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.

------------------------------------------------------------------------

<span id="Parameter-Expansion-Flags"></span>

### 14.3.1 Parameter Expansion Flags

<span id="index-parameter-expansion-flags"></span> <span
id="index-flags_002c-parameter-expansion"></span> <span
id="index-substitution_002c-parameter_002c-flags"></span>

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 interpret these
as character codes. Output the corresponding characters. 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 [Prompt
Expansion](Prompt-Expansion.html#Prompt-Expansion)). If this flag is
given twice, full prompt expansion is done on the resulting words,
depending on the setting of the PROMPT_PERCENT, PROMPT_SUBST and
PROMPT_BANG options.

@  
In double quotes, array elements are put into separate words. E.g.,
‘"${(@)foo}"’ is equivalent to ‘"${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,

<div class="example">

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

</div>

works if $str is ‘a\*b’ but not if it is ‘a b’, whereas

<div class="example">

```zsh
pattern=${(b)str}
[[ $str = ${~pattern} ]]
```

</div>

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 [Filename
Expansion](#Filename-Expansion).

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

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. ‘+’ and ‘-’ are not
treated specially; they are treated as any other non-digit. Integers
with more initial zeroes are sorted before those with fewer or none.
Hence the array ‘foo+24 foo1 foo02 foo2 foo3 foo20 foo23’ is sorted into
the order shown. May be combined with ‘i’ or ‘O’.

\-  
As n, but a leading minus sign indicates a negative decimal integer. A
leading minus sign not followed by an integer does not trigger numeric
sorting. Note that ‘+’ signs are not handled specially (this may change
in the future).

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’, ‘n’ or
‘-’.

O  
Sort the resulting words in descending order; ‘O’ without ‘a’, ‘i’, ‘n’
or ‘-’ sorts in reverse lexical order. May be combined with ‘a’, ‘i’,
‘n’ or ‘-’ 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 $’\\`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
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 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

tied  
for parameters tied to another parameter in the manner of PATH
(colon-separated list) and path (array), whether these are special
parameters or user-defined with ‘typeset -T’

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,

<div class="example">

```zsh
sep=:
val=a:b:c
print ${(ps.$sep.)val}
```

</div>

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,

<div class="example">

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

</div>

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. <span
id="index-SH_005fWORD_005fSPLIT_002c-use-of"></span> 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 unit, however certain Asian character sets and certain
special effects use wider characters; combining characters have zero
width. would actually be displayed will vary.

If the m is repeated, the character either counts zero (if it has 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:

<div class="example">

```zsh
line="one::three"
print -l "${(s.:.)line}"
```

</div>

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.
The following options are available:

(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, I, and \* 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:

<div class="example">

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

</div>

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

<div class="example">

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

</div>

(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:

<div class="example">

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

</div>

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

The `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. 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

<div class="example">

```zsh
which switch is the right switch for Ipswich?
```

</div>

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.

\*  
<span id="index-EXTENDED_005fGLOB_002c-enable"></span>

Enable EXTENDED_GLOB for substitution via ${.../...} or ${...//...}.
Note that ‘\*\*’ does not disable extendedglob.

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 *R*est).

------------------------------------------------------------------------

<span id="Rules"></span>

### 14.3.2 Rules

<span id="index-parameter-expansion-rules"></span> <span
id="index-rules_002c-parameter-expansion"></span> <span
id="index-substitution_002c-parameter_002c-rules"></span>

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
[Modifiers](#Modifiers) in [History Expansion](#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.

------------------------------------------------------------------------

<span id="Examples"></span>

### 14.3.3 Examples

<span id="index-parameter-expansion_002c-examples"></span>

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.

------------------------------------------------------------------------

<span id="Command-Substitution"></span> <span
id="Command-Substitution-1"></span>

## 14.4 Command Substitution

<span id="index-command-substitution"></span> <span
id="index-substitution_002c-command"></span>

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. <span
id="index-IFS_002c-use-of-1"></span>

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.

------------------------------------------------------------------------

<span id="Arithmetic-Expansion"></span> <span
id="Arithmetic-Expansion-1"></span>

## 14.5 Arithmetic Expansion

<span id="index-arithmetic-expansion"></span> <span
id="index-expansion_002c-arithmetic"></span>

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 [Arithmetic
Evaluation](Arithmetic-Evaluation.html#Arithmetic-Evaluation).

------------------------------------------------------------------------

<span id="Brace-Expansion"></span> <span id="Brace-Expansion-1"></span>

## 14.6 Brace Expansion

<span id="index-brace-expansion"></span> <span
id="index-expansion_002c-brace"></span>

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 `n3`th 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 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. <span
id="index-BRACE_005fCCL_002c-use-of"></span> 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 [Parameter Expansion](#Parameter-Expansion) above.

------------------------------------------------------------------------

<span id="Filename-Expansion"></span> <span
id="Filename-Expansion-1"></span>

## 14.7 Filename Expansion

<span id="index-filename-expansion"></span> <span
id="index-expansion_002c-filename"></span>

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. <span
id="index-PUSHD_005fMINUS_002c-use-of"></span> The PUSHD_MINUS option
exchanges the effects of ‘\~+’ and ‘\~-’ where they are followed by a
number.

------------------------------------------------------------------------

<span id="Dynamic-named-directories"></span> <span
id="Dynamic-named-directories-1"></span>

### 14.7.1 Dynamic named directories

<span id="index-directories_002c-named_002c-dynamic"></span> <span
id="index-named-directories_002c-dynamic"></span> <span
id="index-dynamic-named-directories"></span>

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

<div class="example">

```zsh
reply=(s 16)
```

</div>

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 [Completion
System](Completion-System.html#Completion-System).

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.

<div class="example">

```zsh
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
}
```

</div>

------------------------------------------------------------------------

<span id="Static-named-directories"></span> <span
id="Static-named-directories-1"></span>

### 14.7.2 Static named directories

<span id="index-directories_002c-named_002c-static"></span> <span
id="index-named-directories_002c-static"></span> <span
id="index-static-named-directories"></span>

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.

------------------------------------------------------------------------

<span id="g_t_0060_003d_0027-expansion"></span> <span
id="g_t_0060_003d_0027-expansion-1"></span>

### 14.7.3 ‘=’ 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.

------------------------------------------------------------------------

<span id="Notes"></span> <span id="Notes-1"></span>

### 14.7.4 Notes

<span id="index-filename-expansion_002c-notes"></span>

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.

------------------------------------------------------------------------

<span id="Filename-Generation"></span> <span
id="Filename-Generation-1"></span>

## 14.8 Filename Generation

<span id="index-filename-generation"></span>

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. <span
id="index-GLOB_002c-use-of"></span> If the EXTENDED_GLOB option is set,
<span id="index-EXTENDED_005fGLOB_002c-use-of"></span> 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, <span
id="index-NULL_005fGLOB_002c-use-of"></span> in which case the word is
deleted; or unless the NOMATCH option is unset, in which case the word
is left unchanged. <span id="index-NOMATCH_002c-use-of"></span>

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. <span
id="index-GLOB_005fDOTS_002c-use-of"></span> No filename generation
pattern matches the files ‘.’ or ‘..’. In other instances of pattern
matching, the ‘/’ and ‘.’ are not treated specially.

------------------------------------------------------------------------

<span id="Glob-Operators"></span>

### 14.8.1 Glob Operators

<span id="index-glob-operators"></span>

\*  
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. <span
id="index-character-classes"></span> 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

\[:graph:\]  
\[:lower:\]  
The character is a lowercase letter

\[:print:\]  
\[:punct:\]  
\[:space:\]  
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; this test respects the POSIX_IDENTIFIERS option

\[:IFS:\]  
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 [Parameters Used By The
Shell](Parameters.html#Parameters-Used-By-The-Shell).

\[:INCOMPLETE:\]  
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
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.)

------------------------------------------------------------------------

<span id="ksh_002dlike-Glob-Operators"></span>

### 14.8.2 ksh-like Glob Operators

<span id="index-KSH_005fGLOB_002c-use-of"></span>

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 ‘(^(...))’.)

------------------------------------------------------------------------

<span id="Precedence"></span>

### 14.8.3 Precedence

<span id="index-precedence-of-glob-operators"></span>

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.

------------------------------------------------------------------------

<span id="Globbing-Flags"></span>

### 14.8.4 Globbing Flags

<span id="index-globbing-flags"></span> <span
id="index-glob-flags"></span>

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.

<span id="index-match"></span> <span id="index-mbegin"></span> <span
id="index-mend"></span>

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,

<div class="example">

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

</div>

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.

c`N`,`M`  
The flag (#c`N`,`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 (#c`N`) requires exactly N matches; (#c,`M`)
is equivalent to specifying `N` as 0; (#c`N`,) specifies that there is
no maximum limit on the number of matches.

<span id="index-MATCH"></span> <span id="index-MBEGIN"></span> <span
id="index-MEND"></span>

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,

<div class="example">

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

</div>

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.

a`num`  
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.

------------------------------------------------------------------------

<span id="Approximate-Matching"></span>

### 14.8.5 Approximate Matching

<span id="index-approximate-matching"></span> <span
id="index-matching_002c-approximate"></span>

When matching approximately, the shell keeps a count of the errors
found, which cannot exceed the number specified in the (#a`num`) 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.

------------------------------------------------------------------------

<span id="Recursive-Globbing"></span>

### 14.8.6 Recursive Globbing

<span id="index-recursive-globbing"></span> <span
id="index-globbing_002c-recursive"></span>

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:

<div class="example">

```zsh
ls -ld -- (*/)#bar
```

</div>

or

<div class="example">

```zsh
ls -ld -- **/bar
```

</div>

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:

<div class="example">

```zsh
setopt GLOBSTARSHORT
ls -ld -- **.c
```

</div>

is equivalent to

<div class="example">

```zsh
ls -ld -- **/*.c
```

</div>

------------------------------------------------------------------------

<span id="Glob-Qualifiers"></span>

### 14.8.7 Glob Qualifiers

<span id="index-globbing_002c-qualifiers"></span> <span
id="index-qualifiers_002c-globbing"></span>

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.

<span id="index-BARE_005fGLOB_005fQUAL_002c-use-of"></span>

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 ‘(#q`x`)’ 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 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)

\*  
%  
device files (character or block special)

%b  
block special files

%c  
character special files

r  
owner-readable files (0400)

w  
x  
A  
group-readable files (0040)

I  
E  
R  
world-readable files (0004)

W  
X  
s  
setuid files (04000)

S  
setgid files (02000)

t  
files with the sticky bit (01000)

f`spec`  
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-spec`s. 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.

e`string`  
+`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.

<span id="index-REPLY_002c-use-of-1"></span> <span
id="index-reply_002c-use-of"></span>

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,

<div class="example">

```zsh
nt() { [[ $REPLY -nt $NTREF ]] }
NTREF=reffile
ls -ld -- *(+nt)
```

</div>

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

d`dev`  
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

u`id`  
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’.

g`id`  
like u`id` 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, if any; any symbolic link for
whose target the ‘stat’ system call fails (whatever the cause of the
failure) is treated as a file in its own right

M  
sets the MARK_DIRS option for the current pattern <span
id="index-MARK_005fDIRS_002c-setting-in-pattern"></span>

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 <span
id="index-NULL_005fGLOB_002c-setting-in-pattern"></span>

D  
sets the GLOB_DOTS option for the current pattern <span
id="index-GLOB_005fDOTS_002c-setting-in-pattern"></span>

n  
sets the NUMERIC_GLOB_SORT option for the current pattern <span
id="index-NUMERIC_005fGLOB_005fSORT_002c-setting-in-pattern"></span>

Y`n`  
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 o`c` qualifier is used.

o`c`  
specifies how the names of the files should be sorted. The following
values of `c` sort in the following ways:

n  
By name.

L  
By the size (length) of the files.

l  
By number of links.

a  
By time of last access, youngest first.

m  
By time of last modification, youngest first.

c  
By time of last inode change, youngest first.

d  
By directories: 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.

N  
No sorting is performed.

e`string`  
+`cmd`  
Sort by shell code (see below).

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.

O`c`  
like ‘o’, but sorts in descending order; i.e. ‘\*(^o`c`)’ is the same as
‘\*(O`c`)’ and ‘\*(^O`c`)’ is the same as ‘\*(o`c`)’; ‘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.

P`string`  
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 [Modifiers](#Modifiers) in
[History Expansion](#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:

<div class="example">

```zsh
ls -ld -- *(-/)
```

</div>

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

<div class="example">

```zsh
ls -ld -- *(-@)
```

</div>

lists all broken symbolic links, and

<div class="example">

```zsh
ls -ld -- *(%W)
```

</div>

<div class="example">

```zsh
ls -ld -- *(W,X)
```

</div>

lists all files in the current directory that are

<div class="example">

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

</div>

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

<div class="example">

```zsh
ls -ld -- *.*~(lex|parse).[ch](^D^l1)
```

</div>

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.

<div class="example">

```zsh
print -rC1 b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/)
```

</div>

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’.

------------------------------------------------------------------------

This document was generated on *May 14, 2022* using [*texi2html
5.0*](http://www.nongnu.org/texi2html/).  
Zsh version 5.9, released on May 14, 2022.
