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ZSHEXPN(1) General Commands Manual ZSHEXPN(1)
NAME
zshexpn - zsh expansion and substitution
DESCRIPTION
The following types of expansions are performed in the indicated order in five steps:
History Expansion
This is performed only in interactive shells.
Alias Expansion
Aliases are expanded immediately before the command line is parsed as explained un-
der Aliasing in zshmisc(1).
Process Substitution
Parameter Expansion
Command Substitution
Arithmetic Expansion
Brace Expansion
These five are performed in left-to-right fashion. On each argument, any of the
five steps that are needed are performed one after the other. Hence, for example,
all the parts of parameter expansion are completed before command substitution is
started. After these expansions, all unquoted occurrences of the characters
`\',`'' and `"' are removed.
Filename Expansion
If the SH_FILE_EXPANSION option is set, the order of expansion is modified for com-
patibility with sh and ksh. In that case filename expansion is performed immedi-
ately after alias expansion, preceding the set of five expansions mentioned above.
Filename Generation
This expansion, commonly referred to as globbing, is always done last.
The following sections explain the types of expansion in detail.
HISTORY EXPANSION
History expansion allows you to use words from previous command lines in the command line
you are typing. This simplifies spelling corrections and the repetition of complicated
commands or arguments.
Immediately before execution, each command is saved in the history list, the size of which
is controlled by the HISTSIZE parameter. The one most recent command is always retained
in any case. Each saved command in the history list is called a history event and is as-
signed a number, beginning with 1 (one) when the shell starts up. The history number that
you may see in your prompt (see EXPANSION OF PROMPT SEQUENCES in zshmisc(1)) is the number
that is to be assigned to the next command.
Overview
A history expansion begins with the first character of the histchars parameter, which is
`!' by default, and may occur anywhere on the command line, including inside double quotes
(but not inside single quotes '...' or C-style quotes $'...' nor when escaped with a back-
slash).
The first character is followed by an optional event designator (see the section `Event
Designators') and then an optional word designator (the section `Word Designators'); if
neither of these designators is present, no history expansion occurs.
Input lines containing history expansions are echoed after being expanded, but before any
other expansions take place and before the command is executed. It is this expanded form
that is recorded as the history event for later references.
History expansions do not nest.
By default, a history reference with no event designator refers to the same event as any
preceding history reference on that command line; if it is the only history reference in a
command, it refers to the previous command. However, if the option CSH_JUNKIE_HISTORY is
set, then every history reference with no event specification always refers to the previ-
ous command.
For example, `!' is the event designator for the previous command, so `!!:1' always refers
to the first word of the previous command, and `!!$' 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 modi-
fiers (see the section `Modifiers') may follow the final `^'. In particular,
`^foo^bar^:G' performs a global substitution.
If the shell encounters the character sequence `!"' in the input, the history mechanism is
temporarily disabled until the current list (see zshmisc(1)) is fully parsed. The `!"' is
removed from the input, and any subsequent `!' characters have no special significance.
A less convenient but more comprehensible form of command history support is provided by
the fc builtin.
Event Designators
An event designator is a reference to a command-line entry in the history list. In the
list below, remember that the initial `!' in each item may be changed to another character
by setting the histchars parameter.
! Start a history expansion, except when followed by a blank, newline, `=' or `('.
If followed immediately by a word designator (see the section `Word Designators'),
this forms a history reference with no event designator (see the section `Over-
view').
!! Refer to the previous command. By itself, this expansion repeats the previous com-
mand.
!n Refer to command-line n.
!-n Refer to the current command-line minus n.
!str Refer to the most recent command starting with str.
!?str[?]
Refer to the most recent command containing str. The trailing `?' is necessary if
this reference is to be followed by a modifier or followed by any text that is not
to be considered part of str.
!# Refer to the current command line typed in so far. The line is treated as if it
were complete up to and including the word before the one with the `!#' reference.
!{...} Insulate a history reference from adjacent characters (if necessary).
Word Designators
A word designator indicates which word or words of a given command line are to be included
in a history reference. A `:' usually separates the event specification from the word
designator. It may be omitted only if the word designator begins with a `^', `$', `*',
`-' or `%'. Word designators include:
0 The first input word (command).
n The nth argument.
^ The first argument. That is, 1.
$ The last argument.
% The word matched by (the most recent) ?str search.
x-y A range of words; x defaults to 0.
* All the arguments, or a null value if there are none.
x* Abbreviates `x-$'.
x- Like `x*' but omitting word $.
Note that a `%' word designator works only when used in one of `!%', `!:%' or `!?str?:%',
and only when used after a !? expansion (possibly in an earlier command). Anything else
results in an error, although the error may not be the most obvious one.
Modifiers
After the optional word designator, you can add a sequence of one or more of the following
modifiers, each preceded by a `:'. These modifiers also work on the result of filename
generation and parameter expansion, except where noted.
a Turn a file name into an absolute path: prepends the current directory, if neces-
sary; 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', re-
gardless of whether `/before/here' exists or what kind of object (dir, file, sym-
link, 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) se-
mantics, 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 defi-
nition 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 fol-
lowed immediately (with no spaces or other separator) by any number of decimal dig-
its, and the value of the resulting number is non-zero, that number of leading com-
ponents is preserved instead of the final component being removed. In an absolute
path the leading `/' is the first component, so, for example, if
var=/my/path/to/something, then ${var:h3} substitutes /my/path. Consecutive `/'s
are treated the same as a single `/'. In parameter substitution, digits may only
be used if the expression is in braces, so for example the short form substitution
$var:h2 is treated as ${var:h}2, not as ${var:h2}. No restriction applies to the
use of digits in history substitution or globbing qualifiers. If more components
are requested than are present, the entire path is substituted (so this does not
trigger a `failed modifier' error in history expansion).
l Convert the words to all lowercase.
p Print the new command but do not execute it. Only works with history expansion.
P Turn a file name into an absolute path, like realpath(3). The resulting path will
be absolute, have neither `.' nor `..' components, and refer to the same directory
entry as the input filename.
Unlike realpath(3), non-existent trailing components are permitted and preserved.
q Quote the substituted words, escaping further substitutions. Works with history
expansion and parameter expansion, though for parameters it is only useful if the
resulting text is to be re-evaluated such as by eval.
Q Remove one level of quotes from the substituted words.
r Remove a filename extension leaving the root name. Strings with no filename exten-
sion 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 ev-
ery occurrence of r for l. Note that the g or :G must appear in exactly the posi-
tion 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 compo-
nents 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 expan-
sion.
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 omit-
ted. Note the same record of the last l and r is maintained across all forms of expan-
sion.
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 parame-
ter 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 de-
scribed in the section FILENAME GENERATION below. This can be used in all the places
where modifiers are available; note, however, that in globbing qualifiers parameter sub-
stitution 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 pat-
terns 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 af-
ter an # to indicate that the pattern must match at the end of the string to be substi-
tuted. The % or # may be quoted with two backslashes.
For example, the following piece of filename generation code with the EXTENDED_GLOB op-
tion:
print -r -- *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/)
takes the expansion of *.c and applies the glob qualifiers in the (#q...) expression,
which consists of a substitution modifier anchored to the start and end of each word (#%).
This turns on backreferences ((#b)), so that the parenthesised subexpression is available
in the replacement string as ${match[1]}. The replacement string is quoted so that the
parameter is not substituted before the start of filename generation.
The following f, F, w and W modifiers work only with parameter expansion and filename gen-
eration. 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 char-
acter can be used instead of the `:'; if `(', `[', or `{' is used as the opening
delimiter, the closing delimiter should be ')', `]', or `}', respectively.
w Makes the immediately following modifier work on each word in the string.
W:sep: Like w but words are considered to be the parts of the string that are separated by
sep. Any character can be used instead of the `:'; opening parentheses are handled
specially, see above.
PROCESS SUBSTITUTION
Each part of a command argument that takes the form `<(list)', `>(list)' or `=(list)' is
subject to process substitution. The expression may be preceded or followed by other
strings except that, to prevent clashes with commonly occurring strings and patterns, the
last form must occur at the start of a command argument, and the forms are only expanded
when first parsing command or assignment arguments. Process substitutions may be used
following redirection operators; in this case, the substitution must appear with no trail-
ing 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 documen-
tation applies. The second form (with the space) is recommended for clarity.
In the case of the < or > forms, the shell runs the commands in list as a subprocess of
the job executing the shell command line. If the system supports the /dev/fd mechanism,
the command argument is the name of the device file corresponding to a file descriptor;
otherwise, if the system supports named pipes (FIFOs), the command argument will be a
named pipe. If the form with > is selected then writing on this special file will provide
input for list. If < is used, then the file passed as an argument will be connected to
the output of the list process. For example,
paste <(cut -f1 file1) <(cut -f3 file2) |
tee >(process1) >(process2) >/dev/null
cuts fields 1 and 3 from the files file1 and file2 respectively, pastes the results to-
gether, 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 sin-
gle-word argument to the here-string redirection <<<. This form produces a file name con-
taining the value of arg after any substitutions have been performed. This is handled en-
tirely 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 descrip-
tor 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 sec-
ond 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 sys-
tems 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 (pro-
vided the MULTIOS option is set) as:
paste <(cut -f1 file1) <(cut -f3 file2) \
> >(process1) > >(process2)
The shell uses pipes instead of FIFOs to implement the latter two process substitutions in
the above example.
There is an additional problem with >(process); when this is attached to an external com-
mand, the parent shell does not wait for process to finish and hence an immediately fol-
lowing command cannot rely on the results being complete. The problem and solution are
the same as described in the section MULTIOS in zshmisc(1). Hence in a simplified version
of the example above:
paste <(cut -f1 file1) <(cut -f3 file2) > >(process)
(note that no MULTIOS are involved), process will be run asynchronously as far as the par-
ent shell is concerned. The workaround is:
{ paste <(cut -f1 file1) <(cut -f3 file2) } > >(process)
The extra processes here are spawned from the parent shell which will wait for their com-
pletion.
Another problem arises any time a job with a substitution that requires a temporary file
is disowned by the shell, including the case where `&!' or `&|' appears at the end of a
command containing a substitution. In that case the temporary file will not be cleaned up
as the shell no longer has any memory of the job. A workaround is to use a subshell, for
example,
(mycmd =(myoutput)) &!
as the forked subshell will wait for the command to finish then remove the temporary file.
A general workaround to ensure a process substitution endures for an appropriate length of
time is to pass it as a parameter to an anonymous shell function (a piece of shell code
that is run immediately with function scope). For example, this code:
() {
print File $1:
cat $1
} =(print This be the verse)
outputs something resembling the following
File /tmp/zsh6nU0kS:
This be the verse
The temporary file created by the process substitution will be deleted when the function
exits.
PARAMETER EXPANSION
The character `$' is used to introduce parameter expansions. See zshparam(1) for a de-
scription of parameters, including arrays, associative arrays, and subscript notation to
access individual array elements.
Note in particular the fact that words of unquoted parameters are not automatically split
on whitespace unless the option SH_WORD_SPLIT is set; see references to this option below
for more details. This is an important difference from other shells. However, as in
other shells, null words are elided from unquoted parameters' expansions.
With default options, after the assignments:
array=("first word" "" "third word")
scalar="only word"
then $array substitutes two words, `first word' and `third word', and $scalar substitutes
a single word `only word'. Note that second element of array was elided. Scalar parame-
ters can be elided too if their value is null (empty). To avoid elision, use quoting as
follows: "$scalar" for scalars and "${array[@]}" or "${(@)array}" for arrays. (The last
two forms are equivalent.)
Parameter expansions can involve flags, as in `${(@kv)aliases}', and other operators, such
as `${PREFIX:-"/usr/local"}'. Parameter expansions can also be nested. These topics will
be introduced below. The full rules are complicated and are noted at the end.
In the expansions discussed below that require a pattern, the form of the pattern is the
same as that used for filename generation; see the section `Filename Generation'. Note
that these patterns, along with the replacement text of any substitutions, are themselves
subject to parameter expansion, command substitution, and arithmetic expansion. In addi-
tion to the following operations, the colon modifiers described in the section `Modifiers'
in the section `History Expansion' can be applied: for example, ${i:s/foo/bar/} performs
string substitution on the expansion of parameter $i.
In the following descriptions, `word' refers to a single word substituted on the command
line, not necessarily a space delimited word.
${name}
The value, if any, of the parameter name is substituted. The braces are required
if the expansion is to be followed by a letter, digit, or underscore that is not to
be interpreted as part of name. In addition, more complicated forms of substitu-
tion 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 appear-
ing 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 ex-
pansion 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 substi-
tuted.
${name-word}
${name:-word}
If name is set, or in the second form is non-null, then substitute its value; oth-
erwise 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 stan-
dard 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; other-
wise, 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 ele-
ments 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 expres-
sion.
${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 (long-
est for `:^^') of name and arrayname, with the elements alternatingly being picked
from them. For `:^', if one of the input arrays is longer, the output will stop
when the end of the shorter array is reached. Thus,
a=(1 2 3 4); b=(a b); print ${a:^b}
will output `1 a 2 b'. For `:^^', then the input is repeated until all of the
longer array has been used up and the above will output `1 a 2 b 3 a 4 b'.
Either or both inputs may be a scalar, they will be treated as an array of length 1
with the scalar as the only element. If either array is empty, the other array is
output with no extra elements inserted.
Currently the following code will output `a b' and `1' as two separate elements,
which can be unexpected. The second print provides a workaround which should con-
tinue to work if this is changed.
a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}"
${name:offset}
${name:offset:length}
This syntax gives effects similar to parameter subscripting in the form
$name[start,end], but is compatible with other shells; note that both offset and
length are interpreted differently from the components of a subscript.
If offset is non-negative, then if the variable name is a scalar substitute the
contents starting offset characters from the first character of the string, and if
name is an array substitute elements starting offset elements from the first ele-
ment. 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 charac-
ters where appropriate.
offset and length undergo the same set of shell substitutions as for scalar assign-
ment; in addition, they are then subject to arithmetic evaluation. Hence, for ex-
ample
print ${foo:3}
print ${foo: 1 + 2}
print ${foo:$(( 1 + 2))}
print ${foo:$(echo 1 + 2)}
all have the same effect, extracting the string starting at the fourth character of
$foo if the substitution would otherwise return a scalar, or the array starting at
the fourth element if $foo would return an array. Note that with the option
KSH_ARRAYS $foo always returns a scalar (regardless of the use of the offset syn-
tax) 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 indi-
cates the ${name:-word} form of substitution. Instead, a space may be inserted be-
fore the -. Furthermore, neither offset nor length may begin with an alphabetic
character or & as these are used to indicate history-style modifiers. To substi-
tute 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 unread-
able); 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 off-
set 0. This usually accesses the first element of the array. However, if the sub-
stitution 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 posi-
tional 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 pat-
tern 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 neces-
sary if the `/' occurs inside a substituted parameter. Note also that the `#', `%'
and `#% are not active if they occur inside a substituted parameter, even at the
start.
If, after quoting rules apply, ${name} expands to an array, the replacements act on
each element individually. Note also the effect of the I and S parameter expansion
flags below; however, the flags M, R, B, E and N are not useful.
For example,
foo="twinkle twinkle little star" sub="t*e" rep="spy"
print ${foo//${~sub}/$rep}
print ${(S)foo//${~sub}/$rep}
Here, the `~' ensures that the text of $sub is treated as a pattern rather than a
plain string. In the first case, the longest match for t*e is substituted and the
result is `spy star', while in the second case, the shortest matches are taken and
the result is `spy spy lispy star'.
${#spec}
If spec is one of the above substitutions, substitute the length in characters of
the result instead of the result itself. If spec is an array expression, substi-
tute 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_IDENTI-
FIERS is set, then braces are required for the # to be treated in this fashion.
${^spec}
Turn on the RC_EXPAND_PARAM option for the evaluation of spec; if the `^' is dou-
bled, turn it off. When this option is set, array expansions of the form
foo${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 ex-
pansion. E.g., ${^var} becomes {$var[1],$var[2],...}, and is processed as de-
scribed in the section `Brace Expansion' below: note, however, the expansion hap-
pens immediately, with any explicit brace expansion happening later. If word
splitting is also in effect the $var[N] may themselves be split into different list
elements.
${=spec}
Perform word splitting using the rules for SH_WORD_SPLIT during the evaluation of
spec, but regardless of whether the parameter appears in double quotes; if the `='
is doubled, turn it off. This forces parameter expansions to be split into sepa-
rate words before substitution, using IFS as a delimiter. This is done by default
in most other shells.
Note that splitting is applied to word in the assignment forms of spec before the
assignment to name is performed. This affects the result of array assignments with
the A flag.
${~spec}
Turn on the GLOB_SUBST option for the evaluation of spec; if the `~' is doubled,
turn it off. When this option is set, the string resulting from the expansion will
be interpreted as a pattern anywhere that is possible, such as in filename expan-
sion 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 ex-
panded.
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} substi-
tutes the value of $foo with both `head' and `tail' deleted. The form with $(...) is of-
ten 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 expres-
sion as described in Array Parameters in zshparam(1).
Note that double quotes may appear around nested expressions, in which case only the part
inside is treated as quoted; for example, ${(f)"$(foo)"} quotes the result of $(foo), but
the flag `(f)' (see below) is applied using the rules for unquoted expansions. Note fur-
ther that quotes are themselves nested in this context; for example, in "${(@f)"$(foo)"}",
there are two sets of quotes, one surrounding the whole expression, the other (redundant)
surrounding the $(foo) as before.
Parameter Expansion Flags
If the opening brace is directly followed by an opening parenthesis, the string up to the
matching closing parenthesis will be taken as a list of flags. In cases where repeating a
flag is meaningful, the repetitions need not be consecutive; for example, `(q%q%q)' means
the same thing as the more readable `(%%qqq)'. The following flags are supported:
# Evaluate the resulting words as numeric expressions and output the characters cor-
responding to the resulting integer. Note that this form is entirely distinct from
use of the # without parentheses.
If the MULTIBYTE option is set and the number is greater than 127 (i.e. not an
ASCII character) it is treated as a Unicode character.
% Expand all % escapes in the resulting words in the same way as in prompts (see EX-
PANSION OF PROMPT SEQUENCES in zshmisc(1)). If this flag is given twice, full
prompt expansion is done on the resulting words, depending on the setting of the
PROMPT_PERCENT, PROMPT_SUBST and PROMPT_BANG options.
@ In double quotes, array elements are put into separate words. E.g., `"${(@)foo}"'
is equivalent to `"${foo[@]}"' and `"${(@)foo[1,2]}"' is the same as `"$foo[1]"
"$foo[2]"'. This is distinct from field splitting by the f, s or z flags, which
still applies within each array element.
A Convert the substitution into an array expression, even if it otherwise would be
scalar. This has lower precedence than subscripting, so one level of nested expan-
sion 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 `${...::=...}'.
If this flag is repeated (as in `AA'), assigns an associative array parameter. As-
signment is made before sorting or padding; if field splitting is active, the word
part is split before assignment. The name part may be a subscripted range for or-
dinary arrays; when assigning an associative array, the word part must be converted
to an array, for example by using `${(AA)=name=...}' to activate field splitting.
Surrounding context such as additional nesting or use of the value in a scalar as-
signment 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 or-
der. 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, in-
cluding the ${~...} switch.
Quoting using one of the q family of flags does not work for this purpose since
quotes are not stripped from non-pattern characters by GLOB_SUBST. In other words,
pattern=${(q)str}
[[ $str = ${~pattern} ]]
works if $str is `a*b' but not if it is `a b', whereas
pattern=${(b)str}
[[ $str = ${~pattern} ]]
is always true for any possible value of $str.
c With ${#name}, count the total number of characters in an array, as if the elements
were concatenated with spaces between them. This is not a true join of the array,
so other expressions used with this flag may have an effect on the elements of the
array before it is counted.
C Capitalize the resulting words. `Words' in this case refers to sequences of al-
phanumeric characters separated by non-alphanumerics, not to words that result from
field splitting.
D Assume the string or array elements contain directories and attempt to substitute
the leading part of these by names. The remainder of the path (the whole of it if
the leading part was not substituted) is then quoted so that the whole string can
be used as a shell argument. This is the reverse of `~' substitution: see the
section FILENAME EXPANSION below.
e Perform single word shell expansions, namely parameter expansion, command substitu-
tion and arithmetic expansion, on the result. Such expansions can be nested but too
deep recursion may have unpredictable effects.
f Split the result of the expansion at newlines. This is a shorthand for `ps:\n:'.
F Join the words of arrays together using newline as a separator. This is a short-
hand 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, se-
quences like `^X' are also processed. With the e option, processes `\M-t' and sim-
ilar 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 val-
ues. 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 ar-
ray, as usual.
L Convert all letters in the result to lower case.
n Sort decimal integers numerically; if the first differing characters of two test
strings are not digits, sorting is lexical. Integers with more initial zeroes are
sorted before those with fewer or none. Hence the array `foo1 foo02 foo2 foo3
foo20 foo23' is sorted into the order shown. May be combined with `i' or `O'.
o Sort the resulting words in ascending order; if this appears on its own the sorting
is lexical and case-sensitive (unless the locale renders it case-insensitive).
Sorting in ascending order is the default for other forms of sorting, so this is
ignored if combined with `a', `i' or `n'.
O Sort the resulting words in descending order; `O' without `a', `i' or `n' sorts in
reverse lexical order. May be combined with `a', `i' or `n' to reverse the order
of sorting.
P This forces the value of the parameter name to be interpreted as a further parame-
ter 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 ap-
plied 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 ex-
panded 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 back-
slashes; unprintable or invalid characters are quoted using the $'\NNN' form, with
separate quotes for each octet.
If this flag is given twice, the resulting words are quoted in single quotes and if
it is given three times, the words are quoted in double quotes; in these forms no
special handling of unprintable or invalid characters is attempted. If the flag is
given four times, the words are quoted in single quotes preceded by a $. Note that
in all three of these forms quoting is done unconditionally, even if this does not
change the way the resulting string would be interpreted by the shell.
If a q- is given (only a single q may appear), a minimal form of single quoting is
used that only quotes the string if needed to protect special characters. Typi-
cally this form gives the most readable output.
If a q+ is given, an extended form of minimal quoting is used that causes unprint-
able characters to be rendered using $'...'. This quoting is similar to that used
by the output of values by the typeset family of commands.
Q Remove one level of quotes from the resulting words.
t Use a string describing the type of the parameter where the value of the parameter
would usually appear. This string consists of keywords separated by hyphens (`-').
The first keyword in the string describes the main type, it can be one of `scalar',
`array', `integer', `float' or `association'. The other keywords describe the type
in more detail:
local for local parameters
left for left justified parameters
right_blanks
for right justified parameters with leading blanks
right_zeros
for right justified parameters with leading zeros
lower for parameters whose value is converted to all lower case when it is ex-
panded
upper for parameters whose value is converted to all upper case when it is ex-
panded
readonly
for readonly parameters
tag for tagged parameters
export for exported parameters
unique for arrays which keep only the first occurrence of duplicated values
hide for parameters with the `hide' flag
hideval
for parameters with the `hideval' flag
special
for special parameters defined by the shell
u Expand only the first occurrence of each unique word.
U Convert all letters in the result to upper case.
v Used with k, substitute (as two consecutive words) both the key and the value of
each associative array element. Used with subscripts, force values to be substi-
tuted 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 spe-
cially but as ordinary strings, similar to interactive shells with the INTERAC-
TIVE_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 sin-
gle 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 char-
acter, or the matching pairs `(...)', `{...}', `[...]', or `<...>', may be used in place
of a colon as delimiters, but note that when a flag takes more than one argument, a
matched pair of delimiters must surround each argument.
p Recognize the same escape sequences as the print builtin in string arguments to any
of the flags described below that follow this argument.
Alternatively, with this option string arguments may be in the form $var in which
case the value of the variable is substituted. Note this form is strict; the
string argument does not undergo general parameter expansion.
For example,
sep=:
val=a:b:c
print ${(ps.$sep.)val}
splits the variable on a :.
~ Strings inserted into the expansion by any of the flags below are to be treated as
patterns. This applies to the string arguments of flags that follow ~ within the
same set of parentheses. Compare with ~ outside parentheses, which forces the en-
tire substituted string to be treated as a pattern. Hence, for example,
[[ "?" = ${(~j.|.)array} ]]
treats `|' as a pattern and succeeds if and only if $array contains the string `?'
as an element. The ~ may be repeated to toggle the behaviour; its effect only
lasts to the end of the parenthesised group.
j:string:
Join the words of arrays together using string as a separator. Note that this oc-
curs 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 oc-
cupying one unit of width.
Control characters are always assumed to be one unit wide; this allows the mecha-
nism to be used for generating repetitions of control characters.
m Only useful together with one of the flags l or r or with the # length operator
when the MULTIBYTE option is in effect. Use the character width reported by the
system in calculating how much of the string it occupies or the overall length of
the string. Most printable characters have a width of one unit, however certain
Asian character sets and certain special effects use wider characters; combining
characters have zero width. Non-printable characters are arbitrarily counted as
zero width; how they would actually be displayed will vary.
If the m is repeated, the character either counts zero (if it has zero width), else
one. For printable character strings this has the effect of counting the number of
glyphs (visibly separate characters), except for the case where combining charac-
ters 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 pad-
ding to the second half. If the string to be padded has odd width the extra pad-
ding 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 fol-
lowing:
line="one::three"
print -l "${(s.:.)line}"
produces two lines of output for one and three and elides the empty field. To
override this behaviour, supply the `(@)' flag as well, i.e. "${(@s.:.)line}".
Z:opts:
As z but takes a combination of option letters between a following pair of delim-
iter characters. With no options the effect is identical to z. (Z+c+) causes com-
ments to be parsed as a string and retained; any field in the resulting array be-
ginning 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 white-
space, else they are treated as if they are shell code delimiters and converted to
semicolons. Options are combined within the same set of delimiters, e.g. (Z+Cn+).
_:flags:
The underscore (_) flag is reserved for future use. As of this revision of zsh,
there are no valid flags; anything following an underscore, other than an empty
pair of delimiters, is treated as an error, and the flag itself has no effect.
The following flags are meaningful with the ${...#...} or ${...%...} forms. The S and I
flags may also be used with the ${.../...} forms.
S With # or ##, search for the match that starts closest to the start of the string
(a `substring match'). Of all matches at a particular position, # selects the
shortest and ## the longest:
% str="aXbXc"
% echo ${(S)str#X*}
abXc
% echo ${(S)str##X*}
a
%
With % or %%, search for the match that starts closest to the end of the string:
% str="aXbXc"
% echo ${(S)str%X*}
aXbc
% echo ${(S)str%%X*}
aXb
%
(Note that % and %% don't search for the match that ends closest to the end of the
string, as one might expect.)
With substitution via ${.../...} or ${...//...}, specifies non-greedy matching,
i.e. that the shortest instead of the longest match should be replaced:
% str="abab"
% echo ${str/*b/_}
_
% echo ${(S)str/*b/_}
_ab
%
I:expr:
Search the exprth match (where expr evaluates to a number). This only applies when
searching for substrings, either with the S flag, or with ${.../...} (only the ex-
prth match is substituted) or ${...//...} (all matches from the exprth on are sub-
stituted). The default is to take the first match.
The exprth match is counted such that there is either one or zero matches from each
starting position in the string, although for global substitution matches overlap-
ping previous replacements are ignored. With the ${...%...} and ${...%%...} forms,
the starting position for the match moves backwards from the end as the index in-
creases, while with the other forms it moves forward from the start.
Hence with the string
which switch is the right switch for Ipswich?
substitutions of the form ${(SI:N:)string#w*ch} as N increases from 1 will match
and remove `which', `witch', `witch' and `wich'; the form using `##' will match and
remove `which switch is the right switch for Ipswich', `witch is the right switch
for Ipswich', `witch for Ipswich' and `wich'. The form using `%' will remove the
same matches as for `#', but in reverse order, and the form using `%%' will remove
the same matches as for `##' in reverse order.
B Include the index of the beginning of the match in the result.
E Include the index one character past the end of the match in the result (note this
is inconsistent with other uses of parameter index).
M Include the matched portion in the result.
N Include the length of the match in the result.
R Include the unmatched portion in the result (the Rest).
Rules
Here is a summary of the rules for substitution; this assumes that braces are present
around the substitution, i.e. ${...}. Some particular examples are given below. Note
that the Zsh Development Group accepts no responsibility for any brain damage which may
occur during the reading of the following rules.
1. Nested substitution
If multiple nested ${...} forms are present, substitution is performed from the in-
side outwards. At each level, the substitution takes account of whether the cur-
rent 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 di-
rectly 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 substi-
tution, 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 de-
sired, 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 evalu-
ated 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 re-
places 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 in-
ternal 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 cur-
rent level, then words of the value are joined with the first character of the pa-
rameter $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 re-
turns an array in both cases), but not to "${${foo[2,4]}[2]}" (the nested substitu-
tion returns a scalar because of the quotes).
7. Modifiers
Any modifiers, as specified by a trailing `#', `%', `/' (possibly doubled) or by a
set of modifiers of the form `:...' (see the section `Modifiers' in the section
`History Expansion'), are applied to the words of the value at this level.
8. Character evaluation
Any `(#)' flag is applied, evaluating the result so far numerically as a character.
9. Length
Any initial `#' modifier, i.e. in the form ${#var}, is used to evaluate the length
of the expression so far.
10. Forced joining
If the `(j)' flag is present, or no `(j)' flag is present but the string is to be
split as given by rule 11., and joining did not take place at rule 5., any words in
the value are joined together using the given string or the first character of $IFS
if none. Note that the `(F)' flag implicitly supplies a string for joining in this
manner.
11. Simple word splitting
If one of the `(s)' or `(f)' flags are present, or the `=' specifier was present
(e.g. ${=var}), the word is split on occurrences of the specified string, or (for =
with neither of the two flags present) any of the characters in $IFS.
If no `(s)', `(f)' or `=' was given, but the word is not quoted and the option
SH_WORD_SPLIT is set, the word is split on occurrences of any of the characters in
$IFS. Note this step, too, takes place at all levels of a nested substitution.
12. Case modification
Any case modification from one of the flags `(L)', `(U)' or `(C)' is applied.
13. Escape sequence replacement
First any replacements from the `(g)' flag are performed, then any prompt-style
formatting from the `(%)' family of flags is applied.
14. Quote application
Any quoting or unquoting using `(q)' and `(Q)' and related flags is applied.
15. Directory naming
Any directory name substitution using `(D)' flag is applied.
16. Visibility enhancement
Any modifications to make characters visible using the `(V)' flag are applied.
17. Lexical word splitting
If the '(z)' flag or one of the forms of the '(Z)' flag is present, the word is
split as if it were a shell command line, so that quotation marks and other
metacharacters are used to decide what constitutes a word. Note this form of
splitting is entirely distinct from that described by rule 11.: it does not use
$IFS, and does not cause forced joining.
18. Uniqueness
If the result is an array and the `(u)' flag was present, duplicate elements are
removed from the array.
19. Ordering
If the result is still an array and one of the `(o)' or `(O)' flags was present,
the array is reordered.
20. RC_EXPAND_PARAM
At this point the decision is made whether any resulting array elements are to be
combined element by element with surrounding text, as given by either the RC_EX-
PAND_PARAM option or the `^' flag.
21. Re-evaluation
Any `(e)' flag is applied to the value, forcing it to be re-examined for new param-
eter substitutions, but also for command and arithmetic substitutions.
22. Padding
Any padding of the value by the `(l.fill.)' or `(r.fill.)' flags is applied.
23. Semantic joining
In contexts where expansion semantics requires a single word to result, all words
are rejoined with the first character of IFS between. So in `${(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 ar-
gument, whether from a scalar or an element of an array, is elided from the list of
arguments inserted into the command line.
Strictly speaking, the removal happens later as the same happens with other forms
of substitution; the point to note here is simply that it occurs after any of the
above parameter operations.
25. Nested parameter name replacement
If the `(P)' flag is present and rule 4. has not applied, the value so far is
treated as a parameter name (which may include a subscript expression) and replaced
with the corresponding value, with internal flags (rule 2.) applied to the new
value.
Examples
The flag f is useful to split a double-quoted substitution line by line. For example,
${(f)"$(<file)"} substitutes the contents of file divided so that each line is an element
of the resulting array. Compare this with the effect of $(<file) alone, which divides the
file up by words, or the same inside double quotes, which makes the entire content of the
file a single string.
The following illustrates the rules for nested parameter expansions. Suppose that $foo
contains the array (bar baz):
"${(@)${foo}[1]}"
This produces the result b. First, the inner substitution "${foo}", which has no
array (@) flag, produces a single word result "bar baz". The outer substitution
"${(@)...[1]}" detects that this is a scalar, so that (despite the `(@)' flag) the
subscript picks the first character.
"${${(@)foo}[1]}"
This produces the result `bar'. In this case, the inner substitution "${(@)foo}"
produces the array `(bar baz)'. The outer substitution "${...[1]}" detects that
this is an array and picks the first word. This is similar to the simple case
"${foo[1]}".
As an example of the rules for word splitting and joining, suppose $foo contains the array
`(ax1 bx1)'. Then
${(s/x/)foo}
produces the words `a', `1 b' and `1'.
${(j/x/s/x/)foo}
produces `a', `1', `b' and `1'.
${(s/x/)foo%%1*}
produces `a' and ` b' (note the extra space). As substitution occurs before either
joining or splitting, the operation first generates the modified array (ax bx),
which is joined to give "ax bx", and then split to give `a', ` b' and `'. The fi-
nal empty string will then be elided, as it is not in double quotes.
COMMAND SUBSTITUTION
A command enclosed in parentheses preceded by a dollar sign, like `$(...)', or quoted with
grave accents, like ``...`', is replaced with its standard output, with any trailing new-
lines deleted. If the substitution is not enclosed in double quotes, the output is broken
into words using the IFS parameter.
The substitution `$(cat foo)' may be replaced by the faster `$(<foo)'. In this case foo
undergoes single word shell expansions (parameter expansion, command substitution and
arithmetic expansion), but not filename generation.
If the option GLOB_SUBST is set, the result of any unquoted command substitution, includ-
ing the special form just mentioned, is eligible for filename generation.
ARITHMETIC EXPANSION
A string of the form `$[exp]' or `$((exp))' is substituted with the value of the arith-
metic expression exp. exp is subjected to parameter expansion, command substitution and
arithmetic expansion before it is evaluated. See the section `Arithmetic Evaluation'.
BRACE EXPANSION
A string of the form `foo{xx,yy,zz}bar' is expanded to the individual words `fooxxbar',
`fooyybar' and `foozzbar'. Left-to-right order is preserved. This construct may be
nested. Commas may be quoted in order to include them literally in a word.
An expression of the form `{n1..n2}', where n1 and n2 are integers, is expanded to every
number between n1 and n2 inclusive. If either number begins with a zero, all the result-
ing numbers will be padded with leading zeroes to that minimum width, but for negative
numbers the - character is also included in the width. If the numbers are in decreasing
order the resulting sequence will also be in decreasing order.
An expression of the form `{n1..n2..n3}', where n1, n2, and n3 are integers, is expanded
as above, but only every n3th number starting from n1 is output. If n3 is negative the
numbers are output in reverse order, this is slightly different from simply swapping n1
and n2 in the case that the step n3 doesn't evenly divide the range. Zero padding can be
specified in any of the three numbers, specifying it in the third can be useful to pad for
example `{-99..100..01}' which is not possible to specify by putting a 0 on either of the
first two numbers (i.e. pad to two characters).
An expression of the form `{c1..c2}', where c1 and c2 are single characters (which may be
multibyte characters), is expanded to every character in the range from c1 to c2 in what-
ever 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 charac-
ter is not printable, appropriate quotation is used to render it printable. If the char-
acter sequence is reversed, the output is in reverse order, e.g. `{d..a}' is substituted
as `d c b a'.
If a brace expression matches none of the above forms, it is left unchanged, unless the
option BRACE_CCL (an abbreviation for `brace character class') is set. In that case, it
is expanded to a list of the individual characters between the braces sorted into the or-
der 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 gen-
eration takes place. In particular, note that this is liable to produce a `no match' er-
ror if either of the two expressions does not match; this is to be contrasted with
*/(foo|bar), which is treated as a single pattern but otherwise has similar effects.
To combine brace expansion with array expansion, see the ${^spec} form described in the
section Parameter Expansion above.
FILENAME EXPANSION
Each word is checked to see if it begins with an unquoted `~'. If it does, then the word
up to a `/', or the end of the word if there is no `/', is checked to see if it can be
substituted in one of the ways described here. If so, then the `~' and the checked por-
tion 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 re-
placed by the directory that many positions from the bottom of the stack. `~-0' is the
bottom of the stack. The PUSHD_MINUS option exchanges the effects of `~+' and `~-' where
they are followed by a number.
Dynamic named directories
If the function zsh_directory_name exists, or the shell variable zsh_directory_name_func-
tions exists and contains an array of function names, then the functions are used to im-
plement dynamic directory naming. The functions are tried in order until one returns sta-
tus zero, so it is important that functions test whether they can handle the case in ques-
tion 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 termi-
nates 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 re-
sults.
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 can-
didate for dynamic naming. The function should either return non-zero status, if the di-
rectory 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 exam-
ple, if the trial directory is /home/myname/src/zsh and the dynamic name for /home/my-
name/src (which has 16 characters) is s, then the function sets
reply=(s 16)
The directory name so returned is compared with possible static names for parts of the di-
rectory path, as described below; it is used if the prefix length matched (16 in the exam-
ple) 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 re-
turned.
The completion system calls `zsh_directory_name c' followed by equivalent calls to ele-
ments of the array zsh_directory_name_functions, if it exists, in order to complete dy-
namic names for directories. The code for this should be as for any other completion
function as described in zshcompsys(1).
As a working example, here is a function that expands any dynamic names beginning with the
string p: to directories below /home/pws/perforce. In this simple case a static name for
the directory would be just as effective.
zsh_directory_name() {
emulate -L zsh
setopt extendedglob
local -a match mbegin mend
if [[ $1 = d ]]; then
# turn the directory into a name
if [[ $2 = (#b)(/home/pws/perforce/)([^/]##)* ]]; then
typeset -ga reply
reply=(p:$match[2] $(( ${#match[1]} + ${#match[2]} )) )
else
return 1
fi
elif [[ $1 = n ]]; then
# turn the name into a directory
[[ $2 != (#b)p:(?*) ]] && return 1
typeset -ga reply
reply=(/home/pws/perforce/$match[1])
elif [[ $1 = c ]]; then
# complete names
local expl
local -a dirs
dirs=(/home/pws/perforce/*(/:t))
dirs=(p:${^dirs})
_wanted dynamic-dirs expl 'dynamic directory' compadd -S\] -a dirs
return
else
return 1
fi
return 0
}
Static named directories
A `~' followed by anything not already covered consisting of any number of alphanumeric
characters or underscore (`_'), hyphen (`-'), or dot (`.') is looked up as a named direc-
tory, 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 di-
rectory 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 direc-
tory name or the full path; the name is used if they are the same length. The parameters
$PWD and $OLDPWD are never abbreviated in this fashion.
`=' expansion
If a word begins with an unquoted `=' and the EQUALS option is set, the remainder of the
word is taken as the name of a command. If a command exists by that name, the word is re-
placed by the full pathname of the command.
Notes
Filename expansion is performed on the right hand side of a parameter assignment, includ-
ing 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 `identi-
fier=expression' becomes eligible for file expansion as described in the previous para-
graph. Quoting the first `=' also inhibits this.
FILENAME GENERATION
If a word contains an unquoted instance of one of the characters `*', `(', `|', `<', `[',
or `?', it is regarded as a pattern for filename generation, unless the GLOB option is un-
set. If the EXTENDED_GLOB option is set, the `^' and `#' characters also denote a pat-
tern; 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 match-
ing pattern is found, the shell gives an error message, unless the NULL_GLOB option is
set, in which case the word is deleted; or unless the NOMATCH option is unset, in which
case the word is left unchanged.
In filename generation, the character `/' must be matched explicitly; also, a `.' must be
matched explicitly at the beginning of a pattern or after a `/', unless the GLOB_DOTS op-
tion is set. No filename generation pattern matches the files `.' or `..'. In other in-
stances of pattern matching, the `/' and `.' are not treated specially.
Glob Operators
* Matches any string, including the null string.
? Matches any character.
[...] Matches any of the enclosed characters. Ranges of characters can be specified by
separating two characters by a `-'. A `-' or `]' may be matched by including it as
the first character in the list. There are also several named classes of charac-
ters, 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 combina-
tions, including any modifications due to local language settings, see ctype(3):
[:alnum:]
The character is alphanumeric
[:alpha:]
The character is alphabetic
[:ascii:]
The character is 7-bit, i.e. is a single-byte character without the top bit
set.
[:blank:]
The character is a blank character
[:cntrl:]
The character is a control character
[:digit:]
The character is a decimal digit
[:graph:]
The character is a printable character other than whitespace
[:lower:]
The character is a lowercase letter
[:print:]
The character is printable
[:punct:]
The character is printable but neither alphanumeric nor whitespace
[:space:]
The character is whitespace
[:upper:]
The character is an uppercase letter
[:xdigit:]
The character is a hexadecimal digit
Another set of named classes is handled internally by the shell and is not sensi-
tive to the locale:
[:IDENT:]
The character is allowed to form part of a shell identifier, such as a pa-
rameter name
[:IFS:]
The character is used as an input field separator, i.e. is contained in the
IFS parameter
[:IFSSPACE:]
The character is an IFS white space character; see the documentation for IFS
in the zshparam(1) manual page.
[:INCOMPLETE:]
Matches a byte that starts an incomplete multibyte character. Note that
there may be a sequence of more than one bytes that taken together form the
prefix of a multibyte character. To test for a potentially incomplete byte
sequence, use the pattern `[[:INCOMPLETE:]]*'. This will never match a se-
quence 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 charac-
ters 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 in-
dividual digits, the [...] form is more efficient.
Be careful when using other wildcards adjacent to patterns of this form; for exam-
ple, <0-9>* will actually match any number whatsoever at the start of the string,
since the `<0-9>' will match the first digit, and the `*' will match any others.
This is a trap for the unwary, but is in fact an inevitable consequence of the rule
that the longest possible match always succeeds. Expressions such as
`<0-9>[^[:digit:]]*' can be used instead.
(...) Matches the enclosed pattern. This is used for grouping. If the KSH_GLOB option
is set, then a `@', `*', `+', `?' or `!' immediately preceding the `(' is treated
specially, as detailed below. The option SH_GLOB prevents bare parentheses from be-
ing 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 `.' ex-
cept `./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 pat-
tern 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 there-
fore be avoided.)
ksh-like Glob Operators
If the KSH_GLOB option is set, the effects of parentheses can be modified by a preceding
`@', `*', `+', `?' or `!'. This character need not be unquoted to have special effects,
but the `(' must be.
@(...) Match the pattern in the parentheses. (Like `(...)'.)
*(...) Match any number of occurrences. (Like `(...)#', except that recursive directory
searching is not supported.)
+(...) Match at least one occurrence. (Like `(...)##', except that recursive directory
searching is not supported.)
?(...) Match zero or one occurrence. (Like `(|...)'.)
!(...) Match anything but the expression in parentheses. (Like `(^(...))'.)
Precedence
The precedence of the operators given above is (highest) `^', `/', `~', `|' (lowest); the
remaining operators are simply treated from left to right as part of a string, with `#'
and `##' applying to the shortest possible preceding unit (i.e. a character, `?', `[...]',
`<...>', or a parenthesised expression). As mentioned above, a `/' used as a directory
separator may not appear inside parentheses, while a `|' must do so; in patterns used in
other contexts than filename generation (for example, in case statements and tests within
`[[...]]'), a `/' is not special; and `/' is also not special after a `~' appearing out-
side parentheses in a filename pattern.
Globbing Flags
There are various flags which affect any text to their right up to the end of the enclos-
ing group or to the end of the pattern; they require the EXTENDED_GLOB option. All take
the form (#X) where X may have one of the following forms:
i Case insensitive: upper or lower case characters in the pattern match upper or
lower case characters.
l Lower case characters in the pattern match upper or lower case characters; upper
case characters in the pattern still only match upper case characters.
I Case sensitive: locally negates the effect of i or l from that point on.
b Activate backreferences for parenthesised groups in the pattern; this does not work
in filename generation. When a pattern with a set of active parentheses is
matched, the strings matched by the groups are stored in the array $match, the in-
dices of the beginning of the matched parentheses in the array $mbegin, and the in-
dices of the end in the array $mend, with the first element of each array corre-
sponding to the first parenthesised group, and so on. These arrays are not other-
wise 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 paren-
thesised groups; only the first nine active parentheses can be referenced.
For example,
foo="a_string_with_a_message"
if [[ $foo = (a|an)_(#b)(*) ]]; then
print ${foo[$mbegin[1],$mend[1]]}
fi
prints `string_with_a_message'. Note that the first set of parentheses is before
the (#b) and does not create a backreference.
Backreferences work with all forms of pattern matching other than filename genera-
tion, but note that when performing matches on an entire array, such as ${ar-
ray#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 parenthe-
ses 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 nec-
essary to match the complete segment: for example, use `X((ab|cd)#)Y' to match a
whole string of either `ab' or `cd' between `X' and `Y', using the value of
$match[1] rather than $match[2].
If the match fails none of the parameters is altered, so in some cases it may be
necessary to initialise them beforehand. If some of the backreferences fail to
match -- which happens if they are in an alternate branch which fails to match, or
if they are followed by # and matched zero times -- then the matched string is set
to the empty string, and the start and end indices are set to -1.
Pattern matching with backreferences is slightly slower than without.
B Deactivate backreferences, negating the effect of the b flag from that point on.
cN,M The flag (#cN,M) can be used anywhere that the # or ## operators can be used except
in the expressions `(*/)#' and `(*/)##' in filename generation, where `/' has spe-
cial meaning; it cannot be combined with other globbing flags and a bad pattern er-
ror occurs if it is misplaced. It is equivalent to the form {N,M} in regular ex-
pressions. The previous character or group is required to match between N and M
times, inclusive. The form (#cN) requires exactly N matches; (#c,M) is equivalent
to specifying N as 0; (#cN,) specifies that there is no maximum limit on the number
of matches.
m Set references to the match data for the entire string matched; this is similar to
backreferencing and does not work in filename generation. The flag must be in ef-
fect 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 be-
ginning and end of the string, respectively. This is most useful in parameter sub-
stitutions, as otherwise the string matched is obvious.
For example,
arr=(veldt jynx grimps waqf zho buck)
print ${arr//(#m)[aeiou]/${(U)MATCH}}
forces all the matches (i.e. all vowels) into uppercase, printing `vEldt jynx
grImps wAqf zhO bUck'.
Unlike backreferences, there is no speed penalty for using match references, other
than the extra substitutions required for the replacement strings in cases such as
the example shown.
M Deactivate the m flag, hence no references to match data will be created.
anum Approximate matching: num errors are allowed in the string matched by the pattern.
The rules for this are described in the next subsection.
s, e Unlike the other flags, these have only a local effect, and each must appear on its
own: `(#s)' and `(#e)' are the only valid forms. The `(#s)' flag succeeds only at
the start of the test string, and the `(#e)' flag succeeds only at the end of the
test string; they correspond to `^' and `$' in standard regular expressions. They
are useful for matching path segments in patterns other than those in filename gen-
eration (where path segments are in any case treated separately). For example,
`*((#s)|/)test((#e)|/)*' matches a path segment `test' in any of the following
strings: test, test/at/start, at/end/test, in/test/middle.
Another use is in parameter substitution; for example `${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 ig-
nored 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 ap-
plied 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-insensi-
tive 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. Fi-
nally, 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 po-
tentially slow.
Approximate Matching
When matching approximately, the shell keeps a count of the errors found, which cannot ex-
ceed the number specified in the (#anum) flags. Four types of error are recognised:
1. Different characters, as in fooxbar and fooybar.
2. Transposition of characters, as in banana and abnana.
3. A character missing in the target string, as with the pattern road and target
string rod.
4. An extra character appearing in the target string, as with stove and strove.
Thus, the pattern (#a3)abcd matches dcba, with the errors occurring by using the first
rule twice and the second once, grouping the string as [d][cb][a] and [a][bc][d].
Non-literal parts of the pattern must match exactly, including characters in character
ranges: hence (#a1)??? matches strings of length four, by applying rule 4 to an empty
part of the pattern, but not strings of length two, since all the ? must match. Other
characters which must match exactly are initial dots in filenames (unless the GLOB_DOTS
option is set), and all slashes in filenames, so that a/bc is two errors from ab/c (the
slash cannot be transposed with another character). Similarly, errors are counted sepa-
rately 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 sepa-
rately 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/avail-
able/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 possi-
ble approximate match. It is best to place the (#a1) after any path segments which are
known to be correct.
Recursive Globbing
A pathname component of the form `(foo/)#' matches a path consisting of zero or more di-
rectories matching the pattern foo.
As a shorthand, `**/' is equivalent to `(*/)#'; note that this therefore matches files in
the current directory as well as subdirectories. Thus:
ls -ld -- (*/)#bar
or
ls -ld -- **/bar
does a recursive directory search for files named `bar' (potentially including the file
`bar' in the current directory). This form does not follow symbolic links; the alterna-
tive 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 re-
vert to their usual effect.
Even shorter forms are available when the option GLOB_STAR_SHORT is set. In that case if
no / immediately follows a ** or *** they are treated as if both a / plus a further * are
present. Hence:
setopt GLOBSTARSHORT
ls -ld -- **.c
is equivalent to
ls -ld -- **/*.c
Glob Qualifiers
Patterns used for filename generation may end in a list of qualifiers enclosed in paren-
theses. The qualifiers specify which filenames that otherwise match the given pattern
will be inserted in the argument list.
If the option BARE_GLOB_QUAL is set, then a trailing set of parentheses containing no `|'
or `(' characters (or `~' if it is special) is taken as a set of glob qualifiers. A glob
subexpression that would normally be taken as glob qualifiers, for example `(^x)', can be
forced to be treated as part of the glob pattern by doubling the parentheses, in this case
producing `((^x))'.
If the option EXTENDED_GLOB is set, a different syntax for glob qualifiers is available,
namely `(#qx)' where x is any of the same glob qualifiers used in the other format. The
qualifiers must still appear at the end of the pattern. However, with this syntax multi-
ple glob qualifiers may be chained together. They are treated as a logical AND of the in-
dividual sets of flags. Also, as the syntax is unambiguous, the expression will be
treated as glob qualifiers just as long any parentheses contained within it are balanced;
appearance of `|', `(' or `~' does not negate the effect. Note that qualifiers will be
recognised in this form even if a bare glob qualifier exists at the end of the pattern,
for example `*(#q*)(.)' will recognise executable regular files if both options are set;
however, mixed syntax should probably be avoided for the sake of clarity. Note that
within conditions using the `[[' form the presence of a parenthesised expression (#q...)
at the end of a string indicates that globbing should be performed; the expression may in-
clude 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 signifi-
cance.
A qualifier may be any one of the following:
/ directories
F `full' (i.e. non-empty) directories. Note that the opposite sense (^F) expands to
empty directories and all non-directories. Use (/^F) for empty directories.
. plain files
@ symbolic links
= sockets
p named pipes (FIFOs)
* executable plain files (0100 or 0010 or 0001)
% device files (character or block special)
%b block special files
%c character special files
r owner-readable files (0400)
w owner-writable files (0200)
x owner-executable files (0100)
A group-readable files (0040)
I group-writable files (0020)
E group-executable files (0010)
R world-readable files (0004)
W world-writable files (0002)
X world-executable files (0001)
s setuid files (04000)
S setgid files (02000)
t files with the sticky bit (01000)
fspec files with access rights matching spec. This spec may be a octal number optionally
preceded by a `=', a `+', or a `-'. If none of these characters is given, the be-
havior is the same as for `='. The octal number describes the mode bits to be ex-
pected, if combined with a `=', the value given must match the file-modes exactly,
with a `+', at least the bits in the given number must be set in the file-modes,
and with a `-', the bits in the number must not be set. Giving a `?' instead of a
octal digit anywhere in the number ensures that the corresponding bits in the
file-modes are not checked, this is only useful in combination with `='.
If the qualifier `f' is followed by any other character anything up to the next
matching character (`[', `{', and `<' match `]', `}', and `>' respectively, any
other character matches itself) is taken as a list of comma-separated sub-specs.
Each sub-spec may be either an octal number as described above or a list of any of
the characters `u', `g', `o', and `a', followed by a `=', a `+', or a `-', followed
by a list of any of the characters `r', `w', `x', `s', and `t', or an octal digit.
The first list of characters specify which access rights are to be checked. If a
`u' is given, those for the owner of the file are used, if a `g' is given, those of
the group are checked, a `o' means to test those of other users, and the `a' says
to test all three groups. The `=', `+', and `-' again says how the modes are to be
checked and have the same meaning as described for the first form above. The second
list of characters finally says which access rights are to be expected: `r' for
read access, `w' for write access, `x' for the right to execute the file (or to
search a directory), `s' for the setuid and setgid bits, and `t' for the sticky
bit.
Thus, `*(f70?)' gives the files for which the owner has read, write, and execute
permission, and for which other group members have no rights, independent of the
permissions for other users. The pattern `*(f-100)' gives all files for which the
owner does not have execute permission, and `*(f:gu+w,o-rx:)' gives the files for
which the owner and the other members of the group have at least write permission,
and for which other users don't have read or execute permission.
estring
+cmd The string will be executed as shell code. The filename will be included in the
list if and only if the code returns a zero status (usually the status of the last
command).
In the first form, the first character after the `e' will be used as a separator
and anything up to the next matching separator will be taken as the string; `[',
`{', and `<' match `]', `}', and `>', respectively, while any other character
matches itself. Note that expansions must be quoted in the string to prevent them
from being expanded before globbing is done. string is then executed as shell
code. The string globqual is appended to the array zsh_eval_context the duration
of execution.
During the execution of string the filename currently being tested is available in
the parameter REPLY; the parameter may be altered to a string to be inserted into
the list instead of the original filename. In addition, the parameter reply may be
set to an array or a string, which overrides the value of REPLY. If set to an ar-
ray, the latter is inserted into the command line word by word.
For example, suppose a directory contains a single file `lonely'. Then the expres-
sion `*(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 al-
phanumeric or underscore. Typically cmd will be the name of a shell function that
contains the appropriate test. For example,
nt() { [[ $REPLY -nt $NTREF ]] }
NTREF=reffile
ls -ld -- *(+nt)
lists all files in the directory that have been modified more recently than ref-
file.
ddev files on the device dev
l[-|+]ct
files having a link count less than ct (-), greater than ct (+), or equal to ct
U files owned by the effective user ID
G files owned by the effective group ID
uid files owned by user ID id if that is a number. Otherwise, id specifies a user
name: the character after the `u' will be taken as a separator and the string be-
tween it and the next matching separator will be taken as a user name. The start-
ing separators `[', `{', and `<' match the final separators `]', `}', and `>', re-
spectively; any other character matches itself. The selected files are those owned
by this user. For example, `u:foo:' or `u[foo]' selects files owned by user `foo'.
gid like uid but with group IDs or names
a[Mwhms][-|+]n
files accessed exactly n days ago. Files accessed within the last n days are se-
lected using a negative value for n (-n). Files accessed more than n days ago are
selected by a positive n value (+n). Optional unit specifiers `M', `w', `h', `m'
or `s' (e.g. `ah5') cause the check to be performed with months (of 30 days),
weeks, hours, minutes or seconds instead of days, respectively. An explicit `d'
for days is also allowed.
Any fractional part of the difference between the access time and the current part
in the appropriate units is ignored in the comparison. For instance, `echo
*(ah-5)' would echo files accessed within the last five hours, while `echo *(ah+5)'
would echo files accessed at least six hours ago, as times strictly between five
and six hours are treated as five hours.
m[Mwhms][-|+]n
like the file access qualifier, except that it uses the file modification time.
c[Mwhms][-|+]n
like the file access qualifier, except that it uses the file inode change time.
L[+|-]n
files less than n bytes (-), more than n bytes (+), or exactly n bytes in length.
If this flag is directly followed by a size specifier `k' (`K'), `m' (`M'), or `p'
(`P') (e.g. `Lk-50') the check is performed with kilobytes, megabytes, or blocks
(of 512 bytes) instead. (On some systems additional specifiers are available for
gigabytes, `g' or `G', and terabytes, `t' or `T'.) If a size specifier is used a
file is regarded as "exactly" the size if the file size rounded up to the next unit
is equal to the test size. Hence `*(Lm1)' matches files from 1 byte up to 1
Megabyte inclusive. Note also that the set of files "less than" the test size only
includes files that would not match the equality test; hence `*(Lm-1)' only matches
files of zero size.
^ negates all qualifiers following it
- toggles between making the qualifiers work on symbolic links (the default) and the
files they point to
M sets the MARK_DIRS option for the current pattern
T appends a trailing qualifier mark to the filenames, analogous to the LIST_TYPES op-
tion, for the current pattern (overrides M)
N sets the NULL_GLOB option for the current pattern
D sets the GLOB_DOTS option for the current pattern
n sets the NUMERIC_GLOB_SORT option for the current pattern
Yn enables short-circuit mode: the pattern will expand to at most n filenames. If
more than n matches exist, only the first n matches in directory traversal order
will be considered.
Implies oN when no oc qualifier is used.
oc specifies how the names of the files should be sorted. If c is n they are sorted by
name; if it is L they are sorted depending on the size (length) of the files; if l
they are sorted by the number of links; if a, m, or c they are sorted by the time
of the last access, modification, or inode change respectively; if d, files in sub-
directories appear before those in the current directory at each level of the
search -- this is best combined with other criteria, for example `odon' to sort on
names for files within the same directory; if N, no sorting is performed. Note
that a, m, and c compare the age against the current time, hence the first name in
the list is the youngest file. Also note that the modifiers ^ and - are used, so
`*(^-oL)' gives a list of all files sorted by file size in descending order, fol-
lowing 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 opera-
tors, oe and o+ may be repeated, but note that the maximum number of sort operators
of any kind that may appear in any glob expression is 12.
Oc like `o', but sorts in descending order; i.e. `*(^oc)' is the same as `*(Oc)' and
`*(^Oc)' is the same as `*(oc)'; `Od' puts files in the current directory before
those in subdirectories at each level of the search.
[beg[,end]]
specifies which of the matched filenames should be included in the returned list.
The syntax is the same as for array subscripts. beg and the optional end may be
mathematical expressions. As in parameter subscripting they may be negative to make
them count from the last match backward. E.g.: `*(-OL[1,3])' gives a list of the
names of the three largest files.
Pstring
The string will be prepended to each glob match as a separate word. string is de-
limited in the same way as arguments to the e glob qualifier described above. The
qualifier can be repeated; the words are prepended separately so that the resulting
command line contains the words in the same order they were given in the list of
glob qualifiers.
A typical use for this is to prepend an option before all occurrences of a file
name; for example, the pattern `*(P:-f:)' produces the command line arguments `-f
file1 -f file2 ...'
If the modifier ^ is active, then string will be appended instead of prepended.
Prepending and appending is done independently so both can be used on the same glob
expression; for example by writing `*(P:foo:^P:bar:^P:baz:)' which produces the
command line arguments `foo baz file1 bar ...'
More than one of these lists can be combined, separated by commas. The whole list matches
if at least one of the sublists matches (they are `or'ed, the qualifiers in the sublists
are `and'ed). Some qualifiers, however, affect all matches generated, independent of the
sublist in which they are given. These are the qualifiers `M', `T', `N', `D', `n', `o',
`O' and the subscripts given in brackets (`[...]').
If a `:' appears in a qualifier list, the remainder of the expression in parenthesis is
interpreted as a modifier (see the section `Modifiers' in the section `History Expan-
sion'). 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 expres-
sion to be subjected to any global pattern matching options such as NULL_GLOB. Thus:
ls -ld -- *(-/)
lists all directories and symbolic links that point to directories, and
ls -ld -- *(-@)
lists all broken symbolic links, and
ls -ld -- *(%W)
lists all world-writable device files in the current directory, and
ls -ld -- *(W,X)
lists all files in the current directory that are world-writable or world-executable, and
print -rC1 /tmp/foo*(u0^@:t)
outputs the basename of all root-owned files beginning with the string `foo' in /tmp, ig-
noring symlinks, and
ls -ld -- *.*~(lex|parse).[ch](^D^l1)
lists all files having a link count of one whose names contain a dot (but not those start-
ing with a dot, since GLOB_DOTS is explicitly switched off) except for lex.c, lex.h,
parse.c and parse.h.
print -rC1 b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/)
demonstrates how colon modifiers and other qualifiers may be chained together. The ordi-
nary qualifier `.' is applied first, then the colon modifiers in order from left to right.
So if EXTENDED_GLOB is set and the base pattern matches the regular file builtin.pro, the
shell will print `shmiltin.shmo'.
zsh 5.8 February 14, 2020 ZSHEXPN(1)
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On Apache
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