ZSHEXPN(1) General Commands Manual ZSHEXPN(1)
NAME
zshexpn - zsh expansion and substitution
DESCRIPTION
The following types of expansions are performed in the indicated order
in five steps:
History Expansion
This is performed only in interactive shells.
Alias Expansion
Aliases are expanded immediately before the command line is
parsed as explained under Aliasing in zshmisc(1).
Process Substitution
Parameter Expansion
Command Substitution
Arithmetic Expansion
Brace Expansion
These five are performed in left-to-right fashion. On each ar-
gument, 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 charac-
ters `\',`'' and `"' are removed.
Filename Expansion
If the SH_FILE_EXPANSION option is set, the order of expansion
is modified for compatibility with sh and ksh. In that case
filename expansion is performed immediately after alias expan-
sion, preceding the set of five expansions mentioned above.
Filename Generation
This expansion, commonly referred to as globbing, is always done
last.
The following sections explain the types of expansion in detail.
HISTORY EXPANSION
History expansion allows you to use words from previous command lines
in the command line you are typing. This simplifies spelling correc-
tions and the repetition of complicated commands or arguments.
Immediately before execution, each command is saved in the history
list, the size of which is controlled by the HISTSIZE parameter. The
one most recent command is always retained in any case. Each saved
command in the history list is called a history event and is assigned a
number, beginning with 1 (one) when the shell starts up. The history
number that you may see in your prompt (see EXPANSION OF PROMPT SE-
QUENCES 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 com-
mand line, including inside double quotes (but not inside single quotes
'...' or C-style quotes $'...' nor when escaped with a backslash).
The first character is followed by an optional event designator (see
the section `Event Designators') and then an optional word designator
(the section `Word Designators'); if neither of these designators is
present, no history expansion occurs.
Input lines containing history expansions are echoed after being ex-
panded, but before any other expansions take place and before the com-
mand is executed. It is this expanded form that is recorded as the
history event for later references.
History expansions do not nest.
By default, a history reference with no event designator refers to the
same event as any preceding history reference on that command line; if
it is the only history reference in a command, it refers to the previ-
ous command. However, if the option CSH_JUNKIE_HISTORY is set, then
every history reference with no event specification always refers to
the previous command.
For example, `!' is the event designator for the previous command, so
`!!:1' always refers to the first word of the previous command, and
`!!$' 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, re-
spectively, of the same event referenced by the nearest other history
reference preceding them on the current command line, or to the previ-
ous command if there is no preceding reference.
The character sequence `^foo^bar' (where `^' is actually the second
character of the histchars parameter) repeats the last command, replac-
ing the string foo with bar. More precisely, the sequence `^foo^bar^'
is synonymous with `!!:s^foo^bar^', hence other modifiers (see the sec-
tion `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 sup-
port is provided by the fc builtin.
Event Designators
An event designator is a reference to a command-line entry in the his-
tory list. In the list below, remember that the initial `!' in each
item may be changed to another character by setting the histchars pa-
rameter.
! Start a history expansion, except when followed by a blank, new-
line, `=' or `('. If followed immediately by a word designator
(see the section `Word Designators'), this forms a history ref-
erence with no event designator (see the section `Overview').
!! Refer to the previous command. By itself, this expansion re-
peats the previous command.
!n Refer to command-line n.
!-n Refer to the current command-line minus n.
!str Refer to the most recent command starting with str.
!?str[?]
Refer to the most recent command containing str. The trailing
`?' is necessary if this reference is to be followed by a modi-
fier or followed by any text that is not to be considered part
of str.
!# Refer to the current command line typed in so far. The line is
treated as if it were complete up to and including the word be-
fore the one with the `!#' reference.
!{...} Insulate a history reference from adjacent characters (if neces-
sary).
Word Designators
A word designator indicates which word or words of a given command line
are to be included in a history reference. A `:' 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 modi-
fiers also work on the result of filename generation and parameter ex-
pansion, except where noted.
a Turn a file name into an absolute path: prepends the current
directory, if necessary; remove `.' path segments; and remove
`..' path segments and the segments that immediately precede
them.
This transformation is agnostic about what is in the filesystem,
i.e. is on the logical, not the physical directory. It takes
place in the same manner as when changing directories when nei-
ther of the options CHASE_DOTS or CHASE_LINKS is set. For exam-
ple, `/before/here/../after' is always transformed to `/be-
fore/after', regardless of whether `/before/here' exists or what
kind of object (dir, file, symlink, etc.) it is.
A Turn a file name into an absolute path as the `a' modifier does,
and then pass the result through the realpath(3) library func-
tion to resolve symbolic links.
Note: on systems that do not have a realpath(3) library func-
tion, symbolic links are not resolved, so on those systems `a'
and `A' are equivalent.
Note: foo:A and realpath(foo) are different on some inputs. For
realpath(foo) semantics, see the `P` modifier.
c Resolve a command name into an absolute path by searching the
command path given by the PATH variable. This does not work for
commands containing directory parts. Note also that this does
not usually work as a glob qualifier unless a file of the same
name is found in the current directory.
e Remove all but the part of the filename extension following the
`.'; see the definition of the filename extension in the de-
scription of the r modifier below. Note that according to that
definition the result will be empty if the string ends with a
`.'.
h [ digits ]
Remove a trailing pathname component, shortening the path by one
directory level: this is the `head' of the pathname. This works
like `dirname'. If the h is followed immediately (with no spa-
ces or other separator) by any number of decimal digits, and the
value of the resulting number is non-zero, that number of lead-
ing components is preserved instead of the final component being
removed. In an absolute path the leading `/' is the first com-
ponent, 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 his-
tory substitution or globbing qualifiers. If more components
are requested than are present, the entire path is substituted
(so this does not trigger a `failed modifier' error in history
expansion).
l Convert the words to all lowercase.
p Print the new command but do not execute it. Only works with
history expansion.
P Turn a file name into an absolute path, like realpath(3). The
resulting path will be absolute, will refer to the same direc-
tory entry as the input filename, and none of its components
will be symbolic links or equal to `.' or `..'.
Unlike realpath(3), non-existent trailing components are permit-
ted and preserved.
q Quote the substituted words, escaping further substitutions.
Works with history expansion and parameter expansion, though for
parameters it is only useful if the resulting text is to be
re-evaluated such as by eval.
Q Remove one level of quotes from the substituted words.
r Remove a filename extension leaving the root name. Strings with
no filename extension are not altered. A filename extension is
a `.' followed by any number of characters (including zero) that
are neither `.' nor `/' and that continue to the end of the
string. For example, the extension of `foo.orig.c' is `.c', and
`dir.c/foo' has no extension.
s/l/r[/]
Substitute r for l as described below. The substitution is done
only for the first string that matches l. For arrays and for
filename generation, this applies to each word of the expanded
text. See below for further notes on substitutions.
The forms `gs/l/r' and `s/l/r/:G' perform global substitution,
i.e. substitute every occurrence of r for l. Note that the g or
:G must appear in exactly the position shown.
See further notes on this form of substitution below.
& Repeat the previous s substitution. Like s, may be preceded im-
mediately by a g. In parameter expansion the & must appear in-
side braces, and in filename generation it must be quoted with a
backslash.
t [ digits ]
Remove all leading pathname components, leaving the final compo-
nent (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 expansion.
The s/l/r/ substitution works as follows. By default the left-hand
side of substitutions are not patterns, but character strings. Any
character can be used as the delimiter in place of `/'. A backslash
quotes the delimiter character. The character `&', in the
right-hand-side r, is replaced by the text from the left-hand-side l.
The `&' can be quoted with a backslash. A null l uses the previous
string either from the previous l or from the contextual scan string s
from `!?s'. You can omit the rightmost delimiter if a newline immedi-
ately follows r; the rightmost `?' in a context scan can similarly be
omitted. Note the same record of the last l and r is maintained across
all forms of expansion.
Note that if a `&' is used within glob qualifiers an extra backslash is
needed as a & is a special character in this case.
Also note that the order of expansions affects the interpretation of l
and r. When used in a history expansion, which occurs before any other
expansions, l and r are treated as literal strings (except as explained
for HIST_SUBST_PATTERN below). When used in parameter expansion, the
replacement of r into the parameter's value is done first, and then any
additional process, parameter, command, arithmetic, or brace references
are applied, which may evaluate those substitutions and expansions more
than once if l appears more than once in the starting value. When used
in a glob qualifier, any substitutions or expansions are performed once
at the time the qualifier is parsed, even before the `:s' expression
itself is divided into l and r sides.
If the option HIST_SUBST_PATTERN is set, l is treated as a pattern of
the usual form described in the section FILENAME GENERATION below.
This can be used in all the places where modifiers are available; note,
however, that in globbing qualifiers parameter substitution has already
taken place, so parameters in the replacement string should be quoted
to ensure they are replaced at the correct time. Note also that com-
plicated patterns used in globbing qualifiers may need the extended
glob qualifier notation (#q:s/.../.../) in order for the shell to rec-
ognize the expression as a glob qualifier. Further, note that bad pat-
terns in the substitution are not subject to the NO_BAD_PATTERN option
so will cause an error.
When HIST_SUBST_PATTERN is set, l may start with a # to indicate that
the pattern must match at the start of the string to be substituted,
and a % may appear at the start or after an # to indicate that the pat-
tern must match at the end of the string to be substituted. The % or #
may be quoted with two backslashes.
For example, the following piece of filename generation code with the
EXTENDED_GLOB option:
print -r -- *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/)
takes the expansion of *.c and applies the glob qualifiers in the
(#q...) expression, which consists of a substitution modifier anchored
to the start and end of each word (#%). This turns on backreferences
((#b)), so that the parenthesised subexpression is available in the re-
placement string as ${match[1]}. The replacement string is quoted so
that the parameter is not substituted before the start of filename gen-
eration.
The following f, F, w and W modifiers work only with parameter expan-
sion and filename generation. They are listed here to provide a single
point of reference for all modifiers.
f Repeats the immediately (without a colon) following modifier un-
til the resulting word doesn't change any more.
F:expr:
Like f, but repeats only n times if the expression expr evalu-
ates to n. Any character can be used instead of the `:'; 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 expres-
sion may be preceded or followed by other strings except that, to pre-
vent clashes with commonly occurring strings and patterns, the last
form must occur at the start of a command argument, and the forms are
only expanded when first parsing command or assignment arguments.
Process substitutions may be used following redirection operators; in
this case, the substitution must appear with no trailing string.
Note that `<<(list)' is not a special syntax; it is equivalent to `<
<(list)', redirecting standard input from the result of process substi-
tution. Hence all the following documentation applies. The second
form (with the space) is recommended for clarity.
In the case of the < or > forms, the shell runs the commands in list as
a subprocess of the job executing the shell command line. If the sys-
tem 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 spe-
cial file will provide input for list. If < is used, then the file
passed as an argument will be connected to the output of the list
process. For example,
paste <(cut -f1 file1) <(cut -f3 file2) |
tee >(process1) >(process2) >/dev/null
cuts fields 1 and 3 from the files file1 and file2 respectively, pastes
the results together, and sends it to the processes process1 and
process2.
If =(...) is used instead of <(...), then the file passed as an argu-
ment will be the name of a temporary file containing the output of the
list process. This may be used instead of the < form for a program
that expects to lseek (see lseek(2)) on the input file.
There is an optimisation for substitutions of the form =(<<<arg), where
arg is a single-word argument to the here-string redirection <<<. This
form produces a file name containing the value of arg after any substi-
tutions have been performed. This is handled entirely within the cur-
rent 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 implementa-
tion of <(...) have drawbacks. In the former case, some programmes may
automatically close the file descriptor in question before examining
the file on the command line, particularly if this is necessary for se-
curity reasons such as when the programme is running setuid. In the
second case, if the programme does not actually open the file, the sub-
shell attempting to read from or write to the pipe will (in a typical
implementation, different operating systems may have different behav-
iour) block for ever and have to be killed explicitly. In both cases,
the shell actually supplies the information using a pipe, so that pro-
grammes that expect to lseek (see lseek(2)) on the file will not work.
Also note that the previous example can be more compactly and effi-
ciently written (provided the MULTIOS option is set) as:
paste <(cut -f1 file1) <(cut -f3 file2) > >(process1) > >(process2)
The shell uses pipes instead of FIFOs to implement the latter two
process substitutions in the above example.
There is an additional problem with >(process); when this is attached
to an external command, the parent shell does not wait for process to
finish and hence an immediately following command cannot rely on the
results being complete. The problem and solution are the same as de-
scribed in the section MULTIOS in zshmisc(1). Hence in a simplified
version of the example above:
paste <(cut -f1 file1) <(cut -f3 file2) > >(process)
(note that no MULTIOS are involved), process will be run asynchronously
as far as the parent shell is concerned. The workaround is:
{ paste <(cut -f1 file1) <(cut -f3 file2) } > >(process)
The extra processes here are spawned from the parent shell which will
wait for their completion.
Another problem arises any time a job with a substitution that requires
a temporary file is disowned by the shell, including the case where
`&!' or `&|' appears at the end of a command containing a substitution.
In that case the temporary file will not be cleaned up as the shell no
longer has any memory of the job. A workaround is to use a subshell,
for example,
(mycmd =(myoutput)) &!
as the forked subshell will wait for the command to finish then remove
the temporary file.
A general workaround to ensure a process substitution endures for an
appropriate length of time is to pass it as a parameter to an anonymous
shell function (a piece of shell code that is run immediately with
function scope). For example, this code:
() {
print File $1:
cat $1
} =(print This be the verse)
outputs something resembling the following
File /tmp/zsh6nU0kS:
This be the verse
The temporary file created by the process substitution will be deleted
when the function exits.
PARAMETER EXPANSION
The character `$' is used to introduce parameter expansions. See zsh-
param(1) for a description of parameters, including arrays, associative
arrays, and subscript notation to access individual array elements.
Note in particular the fact that words of unquoted parameters are not
automatically split on whitespace unless the option SH_WORD_SPLIT is
set; see references to this option below for more details. This is an
important difference from other shells. 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
$scalar substitutes a single word `only word'. Note that second ele-
ment of array was elided. Scalar parameters can be elided too if their
value is null (empty). To avoid elision, use quoting as follows:
"$scalar" for scalars and "${array[@]}" or "${(@)array}" for arrays.
(The last two forms are equivalent.)
Parameter expansions can involve flags, as in `${(@kv)aliases}', and
other operators, such as `${PREFIX:-"/usr/local"}'. Parameter expan-
sions can also be nested. These topics will be introduced below. The
full rules are complicated and are noted at the end.
In the expansions discussed below that require a pattern, the form of
the pattern is the same as that used for filename generation; see the
section `Filename Generation'. Note that these patterns, along with
the replacement text of any substitutions, are themselves subject to
parameter expansion, command substitution, and arithmetic expansion.
In addition to the following operations, the colon modifiers described
in the section `Modifiers' in the section `History Expansion' can be
applied: for example, ${i:s/foo/bar/} performs string substitution on
the expansion of parameter $i.
In the following descriptions, `word' refers to a single word substi-
tuted 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 let-
ter, digit, or underscore that is not to be interpreted as part
of name. In addition, more complicated forms of substitution
usually require the braces to be present; exceptions, which only
apply if the option KSH_ARRAYS is not set, are a single sub-
script or any colon modifiers appearing after the name, or any
of the characters `^', `=', `~', `#' or `+' appearing before the
name, all of which work with or without braces.
If name is an array parameter, and the KSH_ARRAYS option is not
set, then the value of each element of name is substituted, one
element per word. Otherwise, the expansion results in one word
only; with KSH_ARRAYS, this is the first element of an array.
No field splitting is done on the result unless the
SH_WORD_SPLIT option is set. See also the flags = and
s:string:.
${+name}
If name is the name of a set parameter `1' is substituted, oth-
erwise `0' is substituted.
${name-word}
${name:-word}
If name is set, or in the second form is non-null, then substi-
tute its value; otherwise substitute word. In the second form
name may be omitted, in which case word is always substituted.
${name+word}
${name:+word}
If name is set, or in the second form is non-null, then substi-
tute word; otherwise substitute nothing.
${name=word}
${name:=word}
${name::=word}
In the first form, if name is unset then set it to word; in the
second form, if name is unset or null then set it to word; and
in the third form, unconditionally set name to word. In all
forms, the value of the parameter is then substituted.
${name?word}
${name:?word}
In the first form, if name is set, or in the second form if name
is both set and non-null, then substitute its value; otherwise,
print word and exit from the shell. Interactive shells instead
return to the prompt. If word is omitted, then a standard mes-
sage 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 substitu-
tion 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 sub-
stitute the value of name with the matched portion deleted; oth-
erwise, just substitute the value of name. In the first form,
the smallest matching pattern is preferred; in the second form,
the largest matching pattern is preferred.
${name:#pattern}
If the pattern matches the value of name, then substitute the
empty string; otherwise, just substitute the value of name. If
name is an array the matching array elements are removed (use
the `(M)' flag to remove the non-matched elements).
${name:|arrayname}
If arrayname is the name (N.B., not contents) of an array vari-
able, then any elements contained in arrayname are removed from
the substitution of name. If the substitution is scalar, either
because name is a scalar variable or the expression is quoted,
the elements of arrayname are instead tested against the entire
expression.
${name:*arrayname}
Similar to the preceding substitution, but in the opposite
sense, so that entries present in both the original substitution
and as elements of arrayname are retained and others removed.
${name:^arrayname}
${name:^^arrayname}
Zips two arrays, such that the output array is twice as long as
the shortest (longest for `:^^') of name and arrayname, with the
elements alternatingly being picked from them. For `:^', if one
of the input arrays is longer, the output will stop when the end
of the shorter array is reached. Thus,
a=(1 2 3 4); b=(a b); print ${a:^b}
will output `1 a 2 b'. For `:^^', then the input is repeated
until all of the longer array has been used up and the above
will output `1 a 2 b 3 a 4 b'.
Either or both inputs may be a scalar, they will be treated as
an array of length 1 with the scalar as the only element. If ei-
ther array is empty, the other array is output with no extra el-
ements inserted.
Currently the following code will output `a b' and `1' as two
separate elements, which can be unexpected. The second print
provides a workaround which should continue to work if this is
changed.
a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}"
${name:offset}
${name:offset:length}
This syntax gives effects similar to parameter subscripting in
the form $name[start,end], but is compatible with other shells;
note that both offset and length are interpreted differently
from the components of a subscript.
If offset is non-negative, then if the variable name is a scalar
substitute the contents starting offset characters from the
first character of the string, and if name is an array substi-
tute elements starting offset elements from the first element.
If length is given, substitute that many characters or elements,
otherwise the entire rest of the scalar or array.
A positive offset is always treated as the offset of a character
or element in name from the first character or element of the
array (this is different from native zsh subscript notation).
Hence 0 refers to the first character or element regardless of
the setting of the option KSH_ARRAYS.
A negative offset counts backwards from the end of the scalar or
array, so that -1 corresponds to the last character or element,
and so on.
When positive, length counts from the offset position toward the
end of the scalar or array. When negative, length counts back
from the end. If this results in a position smaller than off-
set, a diagnostic is printed and nothing is substituted.
The option MULTIBYTE is obeyed, i.e. the offset and length count
multibyte characters where appropriate.
offset and length undergo the same set of shell substitutions as
for scalar assignment; in addition, they are then subject to
arithmetic evaluation. Hence, for example
print ${foo:3}
print ${foo: 1 + 2}
print ${foo:$(( 1 + 2))}
print ${foo:$(echo 1 + 2)}
all have the same effect, extracting the string starting at the
fourth character of $foo if the substitution would otherwise re-
turn a scalar, or the array starting at the fourth element if
$foo would return an array. Note that with the option KSH_AR-
RAYS $foo always returns a scalar (regardless of the use of the
offset syntax) and a form such as ${foo[*]:3} is required to ex-
tract elements of an array named foo.
If offset is negative, the - may not appear immediately after
the : as this indicates the ${name:-word} form of substitution.
Instead, a space may be inserted before the -. Furthermore,
neither offset nor length may begin with an alphabetic character
or & as these are used to indicate history-style modifiers. To
substitute a value from a variable, the recommended approach is
to precede it with a $ as this signifies the intention (parame-
ter substitution can easily be rendered unreadable); however, as
arithmetic substitution is performed, the expression ${var:
offs} does work, retrieving the offset from $offs.
For further compatibility with other shells there is a special
case for array offset 0. This usually accesses the first ele-
ment of the array. However, if the substitution refers to the
positional parameter array, e.g. $@ or $*, then offset 0 instead
refers to $0, offset 1 refers to $1, and so on. In other words,
the positional parameter array is effectively extended by
prepending $0. Hence ${*:0:1} substitutes $0 and ${*:1:1} sub-
stitutes $1.
${name/pattern/repl}
${name//pattern/repl}
${name:/pattern/repl}
Replace the longest possible match of pattern in the expansion
of parameter name by string repl. The first form replaces just
the first occurrence, the second form all occurrences, and the
third form replaces only if pattern matches the entire string.
Both pattern and repl are subject to double-quoted substitution,
so that expressions like ${name/$opat/$npat} will work, but obey
the usual rule that pattern characters in $opat are not treated
specially unless either the option GLOB_SUBST is set, or $opat
is instead substituted as ${~opat}.
The pattern may begin with a `#', in which case the pattern must
match at the start of the string, or `%', in which case it must
match at the end of the string, or `#%' in which case the pat-
tern must match the entire string. The repl may be an empty
string, in which case the final `/' may also be omitted. To
quote the final `/' in other cases it should be preceded by a
single backslash; this is not necessary if the `/' occurs inside
a substituted parameter. Note also that the `#', `%' and `#%
are not active if they occur inside a substituted parameter,
even at the start.
If, after quoting rules apply, ${name} expands to an array, the
replacements act on each element individually. Note also the
effect of the I and S parameter expansion flags below; however,
the flags M, R, B, E and N are not useful.
For example,
foo="twinkle twinkle little star" sub="t*e" rep="spy"
print ${foo//${~sub}/$rep}
print ${(S)foo//${~sub}/$rep}
Here, the `~' ensures that the text of $sub is treated as a pat-
tern 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 re-
sult is `spy spy lispy star'.
${#spec}
If spec is one of the above substitutions, substitute the length
in characters of the result instead of the result itself. If
spec is an array expression, substitute the number of elements
of the result. This has the side-effect that joining is skipped
even in quoted forms, which may affect other sub-expressions in
spec. Note that `^', `=', and `~', below, must appear to the
left of `#' when these forms are combined.
If the option POSIX_IDENTIFIERS is not set, and spec is a simple
name, then the braces are optional; this is true even for spe-
cial parameters so e.g. $#- and $#* take the length of the
string $- and the array $* respectively. If POSIX_IDENTIFIERS
is set, then braces are required for the # to be treated in this
fashion.
${^spec}
${^^spec}
Turn on the RC_EXPAND_PARAM option for the evaluation of spec;
if the `^' is doubled, turn it off. When this option is set,
array expansions of the form foo${xx}bar, where the parameter xx
is set to (a b c), are substituted with `fooabar foobbar
foocbar' instead of the default `fooa b cbar'. Note that an
empty array will therefore cause all arguments to be removed.
Internally, each such expansion is converted into the equivalent
list for brace expansion. E.g., ${^var} becomes
{$var[1],$var[2],...}, and is processed as described in the sec-
tion `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}
${==spec}
Perform word splitting using the rules for SH_WORD_SPLIT during
the evaluation of spec, but regardless of whether the parameter
appears in double quotes; if the `=' is doubled, turn it off.
This forces parameter expansions to be split into separate words
before substitution, using IFS as a delimiter. This is done by
default in most other shells.
Note that splitting is applied to word in the assignment forms
of spec before the assignment to name is performed. This af-
fects the result of array assignments with the A flag.
${~spec}
${~~spec}
Turn on the GLOB_SUBST option for the evaluation of spec; if the
`~' is doubled, turn it off. When this option is set, the
string resulting from the expansion will be interpreted as a
pattern anywhere that is possible, such as in filename expansion
and filename generation and pattern-matching contexts like the
right hand side of the `=' and `!=' operators in conditions.
In nested substitutions, note that the effect of the ~ applies
to the result of the current level of substitution. A surround-
ing 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 file-
name generation, but ${${~foo}//\*/*.c} substitutes to the
string *.c, which will not be further expanded.
If a ${...} type parameter expression or a $(...) type command substi-
tution is used in place of name above, it is expanded first and the re-
sult is used as if it were the value of name. Thus it is possible to
perform nested operations: ${${foo#head}%tail} substitutes the value
of $foo with both `head' and `tail' deleted. The form with $(...) is
often useful in combination with the flags described next; see the ex-
amples below. Each name or nested ${...} in a parameter expansion may
also be followed by a subscript expression as described in Array Param-
eters 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 $(foo), but the flag `(f)' (see be-
low) is applied using the rules for unquoted expansions. Note further
that quotes are themselves nested in this context; for example, in
"${(@f)"$(foo)"}", there are two sets of quotes, one surrounding the
whole expression, the other (redundant) surrounding the $(foo) as be-
fore.
Parameter Expansion Flags
If the opening brace is directly followed by an opening parenthesis,
the string up to the matching closing parenthesis will be taken as a
list of flags. In cases where repeating a flag is meaningful, the rep-
etitions need not be consecutive; for example, `(q%q%q)' means the same
thing as the more readable `(%%qqq)'. The following flags are sup-
ported:
# Evaluate the resulting words as numeric expressions and inter-
pret these as character codes. Output the corresponding charac-
ters. Note that this form is entirely distinct from use of the
# without parentheses.
If the MULTIBYTE option is set and the number is greater than
127 (i.e. not an ASCII character) it is treated as a Unicode
character.
% Expand all % escapes in the resulting words in the same way as
in prompts (see EXPANSION OF PROMPT SEQUENCES in zshmisc(1)). If
this flag is given twice, full prompt expansion is done on the
resulting words, depending on the setting of the PROMPT_PERCENT,
PROMPT_SUBST and PROMPT_BANG options.
@ In double quotes, array elements are put into separate words.
E.g., `"${(@)foo}"' is equivalent to `"${foo[@]}"' and
`"${(@)foo[1,2]}"' is the same as `"$foo[1]" "$foo[2]"'. This
is distinct from field splitting by the f, s or z flags, which
still applies within each array element.
A Convert the substitution into an array expression, even if it
otherwise would be scalar. This has lower precedence than sub-
scripting, so one level of nested expansion is required in order
that subscripts apply to array elements. Thus ${${(A)name}[1]}
yields the full value of name when name is scalar.
This assigns an array parameter with `${...=...}', `${...:=...}'
or `${...::=...}'. If this flag is repeated (as in `AA'), as-
signs an associative array parameter. Assignment is made before
sorting or padding; if field splitting is active, the word part
is split before assignment. The name part may be a subscripted
range for ordinary arrays; when assigning an associative array,
the word part must be converted to an array, for example by us-
ing `${(AA)=name=...}' to activate field splitting.
Surrounding context such as additional nesting or use of the
value in a scalar assignment may cause the array to be joined
back into a single string again.
a Sort in array index order; when combined with `O' sort in re-
verse array index order. Note that `a' is therefore equivalent
to the default but `Oa' is useful for obtaining an array's ele-
ments in reverse order.
b Quote with backslashes only characters that are special to pat-
tern matching. This is useful when the contents of the variable
are to be tested using GLOB_SUBST, including the ${~...} switch.
Quoting using one of the q family of flags does not work for
this purpose since quotes are not stripped from non-pattern
characters by GLOB_SUBST. In other words,
pattern=${(q)str}
[[ $str = ${~pattern} ]]
works if $str is `a*b' but not if it is `a b', whereas
pattern=${(b)str}
[[ $str = ${~pattern} ]]
is always true for any possible value of $str.
c With ${#name}, count the total number of characters in an array,
as if the elements were concatenated with spaces between them.
This is not a true join of the array, so other expressions used
with this flag may have an effect on the elements of the array
before it is counted.
C Capitalize the resulting words. `Words' in this case refers to
sequences of alphanumeric characters separated by non-alphanu-
merics, not to words that result from field splitting.
D Assume the string or array elements contain directories and at-
tempt to substitute the leading part of these by names. The re-
mainder 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 expan-
sion, command substitution and arithmetic expansion, on the re-
sult. 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 short-
hand for `ps:\n:'.
F Join the words of arrays together using newline as a separator.
This is a shorthand for `pj:\n:'.
g:opts:
Process escape sequences like the echo builtin when no options
are given (g::). With the o option, octal escapes don't take a
leading zero. With the c option, sequences like `^X' are also
processed. With the e option, processes `\M-t' and similar se-
quences like the print builtin. With both of the o and e op-
tions, 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 (el-
ement names) rather than the values of the elements. Used with
subscripts (including ordinary arrays), force indices or keys to
be substituted even if the subscript form refers to values.
However, this flag may not be combined with subscript ranges.
With the KSH_ARRAYS option a subscript `[*]' or `[@]' is needed
to operate on the whole array, as usual.
L Convert all letters in the result to lower case.
n Sort decimal integers numerically; if the first differing char-
acters of two test strings are not digits, sorting is lexical.
`+' and `-' are not treated specially; they are treated as any
other non-digit. Integers with more initial zeroes are sorted
before those with fewer or none. Hence the array `foo+24 foo1
foo02 foo2 foo3 foo20 foo23' is sorted into the order shown.
May be combined with `i' or `O'.
- As n, but a leading minus sign indicates a negative decimal in-
teger. A leading minus sign not followed by an integer does not
trigger numeric sorting. Note that `+' signs are not handled
specially (this may change in the future).
o Sort the resulting words in ascending order; if this appears on
its own the sorting is lexical and case-sensitive (unless the
locale renders it case-insensitive). Sorting in ascending order
is the default for other forms of sorting, so this is ignored if
combined with `a', `i', `n' or `-'.
O Sort the resulting words in descending order; `O' without `a',
`i', `n' or `-' sorts in reverse lexical order. May be combined
with `a', `i', `n' or `-' to reverse the order of sorting.
P This forces the value of the parameter name to be interpreted as
a further parameter name, whose value will be used where appro-
priate. Note that flags set with one of the typeset family of
commands (in particular case transformations) are not applied to
the value of name used in this fashion.
If used with a nested parameter or command substitution, the re-
sult of that will be taken as a parameter name in the same way.
For example, if you have `foo=bar' and `bar=baz', the strings
${(P)foo}, ${(P)${foo}}, and ${(P)$(echo bar)} will be expanded
to `baz'.
Likewise, if the reference is itself nested, the expression with
the flag is treated as if it were directly replaced by the pa-
rameter name. It is an error if this nested substitution pro-
duces 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 associa-
tive subscripted `elt'.
q Quote characters that are special to the shell in the resulting
words with backslashes; unprintable or invalid characters are
quoted using the $'\NNN' form, with separate quotes for each
octet.
If this flag is given twice, the resulting words are quoted in
single quotes and if it is given three times, the words are
quoted in double quotes; in these forms no special handling of
unprintable or invalid characters is attempted. If the flag is
given four times, the words are quoted in single quotes preceded
by a $. Note that in all three of these forms quoting is done
unconditionally, even if this does not change the way the re-
sulting string would be interpreted by the shell.
If a q- is given (only a single q may appear), a minimal form of
single quoting is used that only quotes the string if needed to
protect special characters. Typically this form gives the most
readable output.
If a q+ is given, an extended form of minimal quoting is used
that causes unprintable characters to be rendered using $'...'.
This quoting is similar to that used by the output of values by
the typeset family of commands.
Q Remove one level of quotes from the resulting words.
t Use a string describing the type of the parameter where the
value of the parameter would usually appear. This string con-
sists of keywords separated by hyphens (`-'). The first keyword
in the string describes the main type, it can be one of
`scalar', `array', `integer', `float' or `association'. The
other keywords describe the type in more detail:
local for local parameters
left for left justified parameters
right_blanks
for right justified parameters with leading blanks
right_zeros
for right justified parameters with leading zeros
lower for parameters whose value is converted to all lower case
when it is expanded
upper for parameters whose value is converted to all upper case
when it is expanded
readonly
for readonly parameters
tag for tagged parameters
tied for parameters tied to another parameter in the manner of
PATH (colon-separated list) and path (array), whether
these are special parameters or user-defined with `type-
set -T'
export for exported parameters
unique for arrays which keep only the first occurrence of dupli-
cated 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 sub-
scripts, force values to be substituted even if the subscript
form refers to indices or keys.
V Make any special characters in the resulting words visible.
w With ${#name}, count words in arrays or strings; the s flag may
be used to set a word delimiter.
W Similar to w with the difference that empty words between re-
peated delimiters are also counted.
X With this flag, parsing errors occurring with the Q, e and #
flags or the pattern matching forms such as `${name#pattern}'
are reported. Without the flag, errors are silently ignored.
z Split the result of the expansion into words using shell parsing
to find the words, i.e. taking into account any quoting in the
value. Comments are not treated specially but as ordinary
strings, similar to interactive shells with the INTERACTIVE_COM-
MENTS option unset (however, see the Z flag below for related
options)
Note that this is done very late, even later than the `(s)'
flag. So to access single words in the result use nested expan-
sions as in `${${(z)foo}[2]}'. Likewise, to remove the quotes in
the resulting words use `${(Q)${(z)foo}}'.
0 Split the result of the expansion on null bytes. This is a
shorthand for `ps:\0:'.
The following flags (except p) are followed by one or more arguments as
shown. Any character, or the matching pairs `(...)', `{...}', `[...]',
or `<...>', may be used in place of a colon as delimiters, but note
that when a flag takes more than one argument, a matched pair of delim-
iters must surround each argument.
p Recognize the same escape sequences as the print builtin in
string arguments to any of the flags described below 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 substi-
tuted. 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 argu-
ments of flags that follow ~ within the same set of parentheses.
Compare with ~ outside parentheses, which forces the entire sub-
stituted string to be treated as a pattern. Hence, for example,
[[ "?" = ${(~j.|.)array} ]]
treats `|' as a pattern and succeeds if and only if $array con-
tains the string `?' as an element. The ~ may be repeated to
toggle the behaviour; its effect only lasts to the end of the
parenthesised group.
j:string:
Join the words of arrays together using string as a separator.
Note that this occurs before field splitting by the s:string:
flag or the SH_WORD_SPLIT option.
l:expr::string1::string2:
Pad the resulting words on the left. Each word will be trun-
cated 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 delim-
iters must be used for each of the three arguments. The space
to the left will be filled with string1 (concatenated as often
as needed) or spaces if string1 is not given. If both string1
and string2 are given, string2 is inserted once directly to the
left of each word, truncated if necessary, before string1 is
used to produce any remaining padding.
If either of string1 or string2 is present but empty, i.e. there
are two delimiters together at that point, the first character
of $IFS is used instead.
If the MULTIBYTE option is in effect, the flag m may also be
given, in which case widths will be used for the calculation of
padding; otherwise individual multibyte characters are treated
as occupying one unit of width.
If the MULTIBYTE option is not in effect, each byte in the
string is treated as occupying one unit of width.
Control characters are always assumed to be one unit wide; this
allows the mechanism to be used for generating repetitions of
control characters.
m Only useful together with one of the flags l or r or with the #
length operator when the MULTIBYTE option is in effect. Use the
character width reported by the system in calculating how much
of the string it occupies or the overall length of the string.
Most printable characters have a width of one unit, however cer-
tain 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 sepa-
rate characters), except for the case where combining characters
themselves have non-zero width (true in certain alphabets).
r:expr::string1::string2:
As l, but pad the words on the right and insert string2 immedi-
ately to the right of the string to be padded.
Left and right padding may be used together. In this case the
strategy is to apply left padding to the first half width of
each of the resulting words, and right padding to the second
half. If the string to be padded has odd width the extra 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 el-
ements are retained inside double quotes is disabled for arrays
generated by splitting; hence the following:
line="one::three"
print -l "${(s.:.)line}"
produces two lines of output for one and three and elides the
empty field. To override this behaviour, supply the `(@)' flag
as well, i.e. "${(@s.:.)line}".
Z:opts:
As z but takes a combination of option letters between a follow-
ing pair of delimiter characters. With no options the effect is
identical to z. The following options are available:
(Z+c+) causes comments to be parsed as a string and retained;
any field in the resulting array beginning with an un-
quoted 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, I, and * flags may also be used with the ${.../...}
forms.
S With # or ##, search for the match that starts closest to the
start of the string (a `substring match'). Of all matches at a
particular position, # selects the shortest and ## the longest:
% 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 long-
est match should be replaced:
% str="abab"
% echo ${str/*b/_}
_
% echo ${(S)str/*b/_}
_ab
%
I:expr:
Search the exprth match (where expr evaluates to a number).
This only applies when searching for substrings, either with the
S flag, or with ${.../...} (only the exprth match is substi-
tuted) or ${...//...} (all matches from the exprth on are sub-
stituted). The default is to take the first match.
The exprth match is counted such that there is either one or
zero matches from each starting position in the string, although
for global substitution matches overlapping previous replace-
ments are ignored. With the ${...%...} and ${...%%...} forms,
the starting position for the match moves backwards from the end
as the index increases, while with the other forms it moves for-
ward from the start.
Hence with the string
which switch is the right switch for Ipswich?
substitutions of the form ${(SI:N:)string#w*ch} as N increases
from 1 will match and remove `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.
* Enable EXTENDED_GLOB for substitution via ${.../...} or
${...//...}. Note that `**' does not disable extendedglob.
B Include the index of the beginning of the match in the result.
E Include the index one character past the end of the match in the
result (note this is inconsistent with other uses of parameter
index).
M Include the matched portion in the result.
N Include the length of the match in the result.
R Include the unmatched portion in the result (the Rest).
Rules
Here is a summary of the rules for substitution; this assumes that
braces are present around the substitution, i.e. ${...}. Some particu-
lar examples are given below. Note that the Zsh Development Group ac-
cepts no responsibility for any brain damage which may occur during the
reading of the following rules.
1. Nested substitution
If multiple nested ${...} forms are present, substitution is
performed from the inside outwards. At each level, the substi-
tution takes account of whether the current value is a scalar or
an array, whether the whole substitution is in double quotes,
and what flags are supplied to the current level of substitu-
tion, just as if the nested substitution were the outermost.
The flags are not propagated up to enclosing substitutions; the
nested substitution will return either a scalar or an array as
determined by the flags, possibly adjusted for quoting. All the
following steps take place where applicable at all levels of
substitution.
Note that, unless the `(P)' flag is present, the flags and any
subscripts apply directly to the value of the nested substitu-
tion; for example, the expansion ${${foo}} behaves exactly the
same as ${foo}. When the `(P)' flag is present in a nested sub-
stitution, 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 un-
dergo all forms of single-word substitution (i.e. not filename
generation), including command substitution, arithmetic expan-
sion 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 file-
name expansion to a full path; the outer substitution then ap-
plies 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 com-
mands, in particular the -L, -R, -Z, -u and -l options for pad-
ding and capitalization, are applied directly to the parameter
value. Note these flags are options to the command, e.g. `type-
set -Z'; they are not the same as the flags used within parame-
ter 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 syntacti-
cally illegal as a parameter name, but if capitalization changes
are desired, use the ${${(P)foo}} form (rule 25.).
3. Parameter subscripting
If the value is a raw parameter reference with a subscript, such
as ${var[3]}, the effect of subscripting is applied directly to
the parameter. Subscripts are evaluated left to right; subse-
quent subscripts apply to the scalar or array value yielded by
the previous subscript. Thus if var is an array, ${var[1][2]}
is the second character of the first word, but ${var[2,4][2]} is
the entire third word (the second word of the range of words two
through four of the original array). Any number of subscripts
may appear. Flags such as `(k)' and `(v)' which alter the re-
sult of subscripting are applied.
4. Parameter name replacement
At the outermost level of nesting only, the `(P)' flag is ap-
plied. This treats the value so far as a parameter name (which
may include a subscript expression) and replaces that with the
corresponding value. This replacement occurs later if the `(P)'
flag appears in a nested substitution.
If the value so far names a parameter that has internal flags
(rule 2.), those internal flags are applied to the new value af-
ter replacement.
5. Double-quoted joining
If the value after this process is an array, and the substitu-
tion appears in double quotes, and neither an `(@)' flag nor a
`#' length operator is present at the current level, then words
of the value are joined with the first character of the parame-
ter $IFS, by default a space, between each word (single word ar-
rays are not modified). If the `(j)' flag is present, that is
used for joining instead of $IFS.
6. Nested subscripting
Any remaining subscripts (i.e. of a nested substitution) are
evaluated at this point, based on whether the value is an array
or a scalar. As with 3., multiple subscripts can appear. Note
that ${foo[2,4][2]} is thus equivalent to ${${foo[2,4]}[2]} and
also to "${${(@)foo[2,4]}[2]}" (the nested substitution returns
an array in both cases), but not to "${${foo[2,4]}[2]}" (the
nested substitution returns a scalar because of the quotes).
7. Modifiers
Any modifiers, as specified by a trailing `#', `%', `/' (possi-
bly 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 numeri-
cally 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 to-
gether 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 `=' spec-
ifier was present (e.g. ${=var}), the word is split on occur-
rences 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 occur-
rences 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 de-
cide what constitutes a word. Note this form of splitting is
entirely distinct from that described by rule 11.: it does not
use $IFS, and does not cause forced joining.
18. Uniqueness
If the result is an array and the `(u)' flag was present, dupli-
cate elements are removed from the array.
19. Ordering
If the result is still an array and one of the `(o)' or `(O)'
flags was present, the array is reordered.
20. RC_EXPAND_PARAM
At this point the decision is made whether any resulting array
elements are to be combined element by element with surrounding
text, as given by either the RC_EXPAND_PARAM option or the `^'
flag.
21. Re-evaluation
Any `(e)' flag is applied to the value, forcing it to be re-ex-
amined for new parameter substitutions, but also for command and
arithmetic substitutions.
22. Padding
Any padding of the value by the `(l.fill.)' or `(r.fill.)' flags
is applied.
23. Semantic joining
In contexts where expansion semantics requires a single word to
result, all words are rejoined with the first character of IFS
between. So in `${(P)${(f)lines}}' the value of ${lines} is
split at newlines, but then must be joined again before the
`(P)' flag can be applied.
If a single word is not required, this rule is skipped.
24. Empty argument removal
If the substitution does not appear in double quotes, any re-
sulting zero-length argument, whether from a scalar or an ele-
ment 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 sim-
ply 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. Com-
pare this with the effect of $(<file) alone, which divides the file up
by words, or the same inside double quotes, which makes the entire con-
tent of the file a single string.
The following illustrates the rules for nested parameter expansions.
Suppose that $foo contains the array (bar baz):
"${(@)${foo}[1]}"
This produces the result b. First, the inner substitution
"${foo}", which has no array (@) flag, produces a single word
result "bar baz". The outer substitution "${(@)...[1]}" detects
that this is a scalar, so that (despite the `(@)' flag) the sub-
script picks the first character.
"${${(@)foo}[1]}"
This produces the result `bar'. In this case, the inner substi-
tution "${(@)foo}" produces the array `(bar baz)'. The outer
substitution "${...[1]}" detects that this is an array and picks
the first word. This is similar to the simple case "${foo[1]}".
As an example of the rules for word splitting and joining, suppose $foo
contains the array `(ax1 bx1)'. Then
${(s/x/)foo}
produces the words `a', `1 b' and `1'.
${(j/x/s/x/)foo}
produces `a', `1', `b' and `1'.
${(s/x/)foo%%1*}
produces `a' and ` b' (note the extra space). As substitution
occurs before either joining or splitting, the operation first
generates the modified array (ax bx), which is joined to give
"ax bx", and then split to give `a', ` b' and `'. The final
empty string will then be elided, as it is not in double quotes.
COMMAND SUBSTITUTION
A command enclosed in parentheses preceded by a dollar sign, like
`$(...)', or quoted with grave accents, like ``...`', is replaced with
its standard output, with any trailing newlines deleted. If the sub-
stitution 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 ex-
pansion, command substitution and arithmetic expansion), but not file-
name generation.
If the option GLOB_SUBST is set, the result of any unquoted command
substitution, including the special form just mentioned, is eligible
for filename generation.
ARITHMETIC EXPANSION
A string of the form `$[exp]' or `$((exp))' is substituted with the
value of the arithmetic expression exp. exp is subjected to parameter
expansion, command substitution and arithmetic expansion before it is
evaluated. See the section `Arithmetic Evaluation'.
BRACE EXPANSION
A string of the form `foo{xx,yy,zz}bar' is expanded to the individual
words `fooxxbar', `fooyybar' and `foozzbar'. Left-to-right order is
preserved. This construct may be nested. Commas may be quoted in or-
der to include them literally in a word.
An expression of the form `{n1..n2}', where n1 and n2 are integers, is
expanded to every number between n1 and n2 inclusive. If either number
begins with a zero, all the resulting numbers will be padded with lead-
ing zeroes to that minimum width, but for negative numbers the - char-
acter 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 in-
tegers, is expanded as above, but only every n3th number starting from
n1 is output. If n3 is negative the numbers are output in reverse or-
der, 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 char-
acters (which may be multibyte characters), is expanded to every char-
acter in the range from c1 to c2 in whatever character sequence is used
internally. For characters with code points below 128 this is US ASCII
(this is the only case most users will need). If any intervening char-
acter is not printable, appropriate quotation is used to render it
printable. If the character sequence is reversed, the output is in re-
verse 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 un-
changed, unless the option BRACE_CCL (an abbreviation for `brace char-
acter class') is set. In that case, it is expanded to a list of the
individual characters between the braces sorted into the order of the
characters in the ASCII character set (multibyte characters are not
currently handled). The syntax is similar to a [...] expression in
filename generation: `-' is treated specially to denote a range of
characters, but `^' or `!' as the first character is treated normally.
For example, `{abcdef0-9}' expands to 16 words 0 1 2 3 4 5 6 7 8 9 a b
c d e f.
Note that brace expansion is not part of filename generation (glob-
bing); an expression such as */{foo,bar} is split into two separate
words */foo and */bar before filename generation takes place. In par-
ticular, note that this is liable to produce a `no match' error if ei-
ther 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 de-
scribed here. If so, then the `~' and the checked portion are replaced
with the appropriate substitute value.
A `~' by itself is replaced by the value of $HOME. A `~' followed by a
`+' or a `-' is replaced by current or previous working directory, re-
spectively.
A `~' followed by a number is replaced by the directory at that posi-
tion in the directory stack. `~0' is equivalent to `~+', and `~1' is
the top of the stack. `~+' followed by a number is replaced by the di-
rectory at that position in the directory stack. `~+0' is equivalent
to `~+', and `~+1' is the top of the stack. `~-' followed by a number
is replaced by the directory that many positions from the bottom of the
stack. `~-0' is the bottom of the stack. The PUSHD_MINUS option ex-
changes the effects of `~+' and `~-' where they are followed by a num-
ber.
Dynamic named directories
If the function zsh_directory_name exists, or the shell variable
zsh_directory_name_functions exists and contains an array of function
names, then the functions are used to implement dynamic directory nam-
ing. The functions are tried in order until one returns status zero,
so it is important that functions test whether they can handle the case
in question and return an appropriate status.
A `~' followed by a string namstr in unquoted square brackets is
treated specially as a dynamic directory name. Note that the first un-
quoted closing square bracket always terminates namstr. The shell
function is passed two arguments: the string n (for name) and namstr.
It should either set the array reply to a single element which is the
directory corresponding to the name and return status zero (executing
an assignment as the last statement is usually sufficient), or it
should return status non-zero. In the former case the element of reply
is used as the directory; in the latter case the substitution is deemed
to have failed. If all functions fail and the option NOMATCH is set,
an error results.
The functions defined as above are also used to see if a directory can
be turned into a name, for example when printing the directory stack or
when expanding %~ in prompts. In this case each function is passed two
arguments: the string d (for directory) and the candidate for dynamic
naming. The function should either return non-zero status, if the di-
rectory cannot be named by the function, or it should set the array re-
ply to consist of two elements: the first is the dynamic name for the
directory (as would appear within `~[...]'), and the second is the pre-
fix length of the directory to be replaced. For example, 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 directory path, as described below; it is used if the
prefix length matched (16 in the example) is longer than that matched
by any static name.
It is not a requirement that a function implements both n and d calls;
for example, it might be appropriate for certain dynamic forms of ex-
pansion not to be contracted to names. In that case any call with the
first argument d should cause a non-zero status to be returned.
The completion system calls `zsh_directory_name c' followed by equiva-
lent calls to elements of the array zsh_directory_name_functions, if it
exists, in order to complete dynamic names for directories. The code
for this should be as for any other completion function as described in
zshcompsys(1).
As a working example, here is a function that expands any dynamic names
beginning with the string p: to directories below /home/pws/perforce.
In this simple case a static name for the directory would be just as
effective.
zsh_directory_name() {
emulate -L zsh
setopt extendedglob
local -a match mbegin mend
if [[ $1 = d ]]; then
# turn the directory into a name
if [[ $2 = (#b)(/home/pws/perforce/)([^/]##)* ]]; then
typeset -ga reply
reply=(p:$match[2] $(( ${#match[1]} + ${#match[2]} )) )
else
return 1
fi
elif [[ $1 = n ]]; then
# turn the name into a directory
[[ $2 != (#b)p:(?*) ]] && return 1
typeset -ga reply
reply=(/home/pws/perforce/$match[1])
elif [[ $1 = c ]]; then
# complete names
local expl
local -a dirs
dirs=(/home/pws/perforce/*(/:t))
dirs=(p:${^dirs})
_wanted dynamic-dirs expl 'dynamic directory' compadd -S\] -a dirs
return
else
return 1
fi
return 0
}
Static named directories
A `~' followed by anything not already covered consisting of any number
of alphanumeric characters or underscore (`_'), hyphen (`-'), or dot
(`.') is looked up as a named directory, and replaced by the value of
that named directory if found. Named directories are typically home
directories for users on the system. They may also be defined if the
text after the `~' is the name of a string shell parameter whose value
begins with a `/'. Note that trailing slashes will be removed from the
path to the directory (though the original parameter is not modified).
It is also possible to define directory names using the -d option to
the hash builtin.
When the shell prints a path (e.g. when expanding %~ in prompts or when
printing the directory stack), the path is checked to see if it has a
named directory as its prefix. If so, then the prefix portion is re-
placed with a `~' followed by the name of the directory. The shorter
of the two ways of referring to the directory is used, i.e. either the
directory name or the full path; the name is used if they are the same
length. The parameters $PWD and $OLDPWD are never abbreviated in this
fashion.
`=' expansion
If a word begins with an unquoted `=' and the EQUALS option is set, the
remainder of the word is taken as the name of a command. If a command
exists by that name, the word is replaced by the full pathname of the
command.
Notes
Filename expansion is performed on the right hand side of a parameter
assignment, including those appearing after commands of the typeset
family. In this case, the right hand side will be treated as a
colon-separated list in the manner of the PATH parameter, so that a `~'
or an `=' following a `:' is eligible for expansion. All such behav-
iour can be disabled by quoting the `~', the `=', or the whole expres-
sion (but not simply the colon); the EQUALS option is also respected.
If the option MAGIC_EQUAL_SUBST is set, any unquoted shell argument in
the form `identifier=expression' becomes eligible for file expansion as
described in the previous paragraph. Quoting the first `=' also in-
hibits this.
FILENAME GENERATION
If a word contains an unquoted instance of one of the characters `*',
`(', `|', `<', `[', or `?', it is regarded as a pattern for filename
generation, unless the GLOB option is unset. If the EXTENDED_GLOB op-
tion is set, the `^' and `#' characters also denote a pattern; other-
wise they are not treated specially by the shell.
The word is replaced with a list of sorted filenames that match the
pattern. If no matching pattern is found, the shell gives an error
message, unless the NULL_GLOB option is set, in which case the word is
deleted; or unless the NOMATCH option is unset, in which case the word
is left unchanged.
In filename generation, the character `/' must be matched explicitly;
also, a `.' must be matched explicitly at the beginning of a pattern or
after a `/', unless the GLOB_DOTS option is set. No filename genera-
tion pattern matches the files `.' or `..'. In other instances of pat-
tern matching, the `/' and `.' are not treated specially.
Glob Operators
* Matches any string, including the null string.
? Matches any character.
[...] Matches any of the enclosed characters. Ranges of characters
can be specified by separating two characters by a `-'. A `-'
or `]' may be matched by including it as the first character in
the list. There are also several named classes of characters,
in the form `[:name:]' with the following meanings. The first
set use the macros provided by the operating system to test for
the given character combinations, including any modifications
due to local language settings, see ctype(3):
[:alnum:]
The character is alphanumeric
[:alpha:]
The character is alphabetic
[:ascii:]
The character is 7-bit, i.e. is a single-byte character
without the top bit set.
[:blank:]
The character is a blank character
[:cntrl:]
The character is a control character
[:digit:]
The character is a decimal digit
[:graph:]
The character is a printable character other than white-
space
[:lower:]
The character is a lowercase letter
[:print:]
The character is printable
[:punct:]
The character is printable but neither alphanumeric nor
whitespace
[:space:]
The character is whitespace
[:upper:]
The character is an uppercase letter
[:xdigit:]
The character is a hexadecimal digit
Another set of named classes is handled internally by the shell
and is not sensitive to the locale:
[:IDENT:]
The character is allowed to form part of a shell identi-
fier, such as a parameter name; this test respects the
POSIX_IDENTIFIERS option
[:IFS:]
The character is used as an input field separator, i.e.
is contained in the IFS parameter
[:IFSSPACE:]
The character is an IFS white space character; see the
documentation for IFS in the zshparam(1) manual page.
[:INCOMPLETE:]
Matches a byte that starts an incomplete multibyte char-
acter. Note that there may be a sequence of more than
one bytes that taken together form the prefix of a multi-
byte character. To test for a potentially incomplete
byte sequence, use the pattern `[[:INCOMPLETE:]]*'. This
will never match a sequence starting with a valid multi-
byte character.
[:INVALID:]
Matches a byte that does not start a valid multibyte
character. Note this may be a continuation byte of an
incomplete multibyte character as any part of a multibyte
string consisting of invalid and incomplete multibyte
characters is treated as single bytes.
[:WORD:]
The character is treated as part of a word; this test is
sensitive to the value of the WORDCHARS parameter
Note that the square brackets are additional to those enclosing
the whole set of characters, so to test for a single alphanu-
meric character you need `[[:alnum:]]'. Named character sets
can be used alongside other types, e.g. `[[:alpha:]0-9]'.
[^...]
[!...] Like [...], except that it matches any character which is not in
the given set.
<[x]-[y]>
Matches any number in the range x to y, inclusive. Either of
the numbers may be omitted to make the range open-ended; hence
`<->' matches any number. To match individual digits, the [...]
form is more efficient.
Be careful when using other wildcards adjacent to patterns of
this form; for example, <0-9>* will actually match any number
whatsoever at the start of the string, since the `<0-9>' will
match the first digit, and the `*' will match any others. This
is a trap for the unwary, but is in fact an inevitable conse-
quence of the rule that the longest possible match always suc-
ceeds. Expressions such as `<0-9>[^[:digit:]]*' can be used in-
stead.
(...) Matches the enclosed pattern. This is used for grouping. If
the KSH_GLOB option is set, then a `@', `*', `+', `?' or `!' im-
mediately preceding the `(' is treated specially, as detailed
below. The option SH_GLOB prevents bare parentheses from being
used in this way, though the KSH_GLOB option is still available.
Note that grouping cannot extend over multiple directories: it
is an error to have a `/' within a group (this only applies for
patterns used in filename generation). There is one exception:
a group of the form (pat/)# appearing as a complete path segment
can match a sequence of directories. For example, foo/(a*/)#bar
matches foo/bar, foo/any/bar, foo/any/anyother/bar, and so on.
x|y Matches either x or y. This operator has lower precedence than
any other. The `|' character must be within parentheses, to
avoid interpretation as a pipeline. The alternatives are tried
in order from left to right.
^x (Requires EXTENDED_GLOB to be set.) Matches anything except the
pattern x. This has a higher precedence than `/', so `^foo/bar'
will search directories in `.' except `./foo' for a file named
`bar'.
x~y (Requires EXTENDED_GLOB to be set.) Match anything that matches
the pattern x but does not match y. This has lower precedence
than any operator except `|', so `*/*~foo/bar' will search for
all files in all directories in `.' and then exclude `foo/bar'
if there was such a match. Multiple patterns can be excluded by
`foo~bar~baz'. In the exclusion pattern (y), `/' and `.' are
not treated specially the way they usually are in globbing.
x# (Requires EXTENDED_GLOB to be set.) Matches zero or more occur-
rences of the pattern x. This operator has high precedence;
`12#' is equivalent to `1(2#)', rather than `(12)#'. It is an
error for an unquoted `#' to follow something which cannot be
repeated; this includes an empty string, a pattern already fol-
lowed 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 occur-
rences of the pattern x. This operator has high precedence;
`12##' is equivalent to `1(2##)', rather than `(12)##'. No more
than two active `#' characters may appear together. (Note the
potential clash with glob qualifiers in the form `1(2##)' which
should therefore be avoided.)
ksh-like Glob Operators
If the KSH_GLOB option is set, the effects of parentheses can be modi-
fied 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 re-
cursive 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 direc-
tory separator may not appear inside parentheses, while a `|' must do
so; in patterns used in other contexts than filename generation (for
example, in case statements and tests within `[[...]]'), a `/' is not
special; and `/' is also not special after a `~' appearing outside
parentheses in a filename pattern.
Globbing Flags
There are various flags which affect any text to their right up to the
end of the enclosing group or to the end of the pattern; they require
the EXTENDED_GLOB option. All take the form (#X) where X may have one
of the following forms:
i Case insensitive: upper or lower case characters in the pattern
match upper or lower case characters.
l Lower case characters in the pattern match upper or lower case
characters; upper case characters in the pattern still only
match upper case characters.
I Case sensitive: locally negates the effect of i or l from that
point on.
b Activate backreferences for parenthesised groups in the pattern;
this does not work in filename generation. When a pattern with
a set of active parentheses is matched, the strings matched by
the groups are stored in the array $match, the indices of the
beginning of the matched parentheses in the array $mbegin, and
the indices of the end in the array $mend, with the first ele-
ment of each array corresponding to the first parenthesised
group, and so on. These arrays are not otherwise special to the
shell. The indices use the same convention as does parameter
substitution, so that elements of $mend and $mbegin may be used
in subscripts; the KSH_ARRAYS option is respected. Sets of
globbing flags are not considered parenthesised groups; only the
first nine active parentheses can be referenced.
For example,
foo="a_string_with_a_message"
if [[ $foo = (a|an)_(#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 backrefer-
ence.
Backreferences work with all forms of pattern matching other
than filename generation, but note that when performing matches
on an entire array, such as ${array#pattern}, or a global sub-
stitution, such as ${param//pat/repl}, only the data for the
last match remains available. In the case of global replace-
ments this may still be useful. See the example for the m flag
below.
The numbering of backreferences strictly follows the order of
the opening parentheses from left to right in the pattern
string, although sets of parentheses may be nested. There are
special rules for parentheses followed by `#' or `##'. Only the
last match of the parenthesis is remembered: for example, in `[[
abab = (#b)([ab])# ]]', only the final `b' is stored in
match[1]. Thus extra parentheses may be necessary to match the
complete segment: for example, use `X((ab|cd)#)Y' to match a
whole string of either `ab' or `cd' between `X' and `Y', using
the value of $match[1] rather than $match[2].
If the match fails none of the parameters is altered, so in some
cases it may be necessary to initialise them beforehand. If
some of the backreferences fail to match -- which happens if
they are in an alternate branch which fails to match, or if they
are followed by # and matched zero times -- then the matched
string is set to the empty string, and the start and end indices
are set to -1.
Pattern matching with backreferences is slightly slower than
without.
B Deactivate backreferences, negating the effect of the b flag
from that point on.
cN,M The flag (#cN,M) can be used anywhere that the # or ## operators
can be used except in the expressions `(*/)#' and `(*/)##' in
filename generation, where `/' has special meaning; it cannot be
combined with other globbing flags and a bad pattern error oc-
curs if it is misplaced. It is equivalent to the form {N,M} in
regular expressions. The previous character or group is re-
quired to match between N and M times, inclusive. The form
(#cN) requires exactly N matches; (#c,M) is equivalent to speci-
fying N as 0; (#cN,) specifies that there is no maximum limit on
the number of matches.
m Set references to the match data for the entire string matched;
this is similar to backreferencing and does not work in filename
generation. The flag must be in effect at the end of the pat-
tern, i.e. not local to a group. The parameters $MATCH, $MBEGIN
and $MEND will be set to the string matched and to the indices
of the beginning and end of the string, respectively. This is
most useful in parameter substitutions, as otherwise the string
matched is obvious.
For example,
arr=(veldt jynx grimps waqf zho buck)
print ${arr//(#m)[aeiou]/${(U)MATCH}}
forces all the matches (i.e. all vowels) into uppercase, print-
ing `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 `$' in standard regular ex-
pressions. They are useful for matching path segments in pat-
terns other than those in filename generation (where path seg-
ments are in any case treated separately). For example,
`*((#s)|/)test((#e)|/)*' matches a path segment `test' in any of
the following strings: test, test/at/start, at/end/test,
in/test/middle.
Another use is in parameter substitution; for example `${ar-
ray/(#s)A*Z(#e)}' will remove only elements of an array which
match the complete pattern `A*Z'. There are other ways of per-
forming 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 actu-
ally 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 glob-
bing flags are ignored by the pattern matching code. This is
intended to support the use of glob qualifiers, see below. The
result is that the pattern `(#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 use-
ful for backreferences and the `(#q.)' will be ignored. Note
that colon modifiers in the glob qualifiers are also not applied
in ordinary pattern matching.
u Respect the current locale in determining the presence of multi-
byte 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 op-
posite of u. This overrides the MULTIBYTE option.
For example, the test string fooxx can be matched by the pattern
(#i)FOOXX, but not by (#l)FOOXX, (#i)FOO(#I)XX or ((#i)FOOX)X. The
string (#ia2)readme specifies case-insensitive matching of readme with
up to two errors.
When using the ksh syntax for grouping both KSH_GLOB and EXTENDED_GLOB
must be set and the left parenthesis should be preceded by @. Note
also that the flags do not affect letters inside [...] groups, in other
words (#i)[a-z] still matches only lowercase letters. Finally, note
that when examining whole paths case-insensitively every directory must
be searched for all files which match, so that a pattern of the form
(#i)/foo/bar/... is potentially slow.
Approximate Matching
When matching approximately, the shell keeps a count of the errors
found, which cannot exceed the number specified in the (#anum) flags.
Four types of error are recognised:
1. Different characters, as in fooxbar and fooybar.
2. Transposition of characters, as in banana and abnana.
3. A character missing in the target string, as with the pattern
road and target string rod.
4. An extra character appearing in the target string, as with stove
and strove.
Thus, the pattern (#a3)abcd matches dcba, with the errors occurring by
using the first rule twice and the second once, grouping the string as
[d][cb][a] and [a][bc][d].
Non-literal parts of the pattern must match exactly, including charac-
ters in character ranges: hence (#a1)??? matches strings of length
four, by applying rule 4 to an empty part of the pattern, but not
strings of length two, since all the ? must match. Other characters
which must match exactly are initial dots in filenames (unless the
GLOB_DOTS option is set), and all slashes in filenames, so that a/bc is
two errors from ab/c (the slash cannot be transposed with another char-
acter). Similarly, errors are counted separately for non-contiguous
strings in the pattern, so that (ab|cd)ef is two errors from aebf.
When using exclusion via the ~ operator, approximate matching is
treated entirely separately for the excluded part and must be activated
separately. Thus, (#a1)README~READ_ME matches READ.ME but not READ_ME,
as the trailing READ_ME is matched without approximation. However,
(#a1)README~(#a1)READ_ME does not match any pattern of the form READ?ME
as all such forms are now excluded.
Apart from exclusions, there is only one overall error count; however,
the maximum errors allowed may be altered locally, and this can be de-
limited by grouping. For example, (#a1)cat((#a0)dog)fox allows one er-
ror in total, which may not occur in the dog section, and the pattern
(#a1)cat(#a0)dog(#a1)fox is equivalent. Note that the point at which
an error is first found is the crucial one for establishing whether to
use approximation; for example, (#a1)abc(#a0)xyz will not match
abcdxyz, because the error occurs at the `x', where approximation is
turned off.
Entire path segments may be matched approximately, so that
`(#a1)/foo/d/is/available/at/the/bar' allows one error in any path seg-
ment. This is much less efficient than without the (#a1), however,
since every directory in the path must be scanned for a possible ap-
proximate match. It is best to place the (#a1) after any path segments
which are known to be correct.
Recursive Globbing
A pathname component of the form `(foo/)#' matches a path consisting of
zero or more directories matching the pattern foo.
As a shorthand, `**/' is equivalent to `(*/)#'; note that this there-
fore matches files in the current directory as well as subdirectories.
Thus:
ls -ld -- (*/)#bar
or
ls -ld -- **/bar
does a recursive directory search for files named `bar' (potentially
including the file `bar' in the current directory). This form does not
follow symbolic links; the alternative form `***/' does, but is other-
wise identical. Neither of these can be combined with other forms of
globbing within the same path segment; in that case, the `*' operators
revert to their usual effect.
Even shorter forms are available when the option GLOB_STAR_SHORT is
set. In that case if no / immediately follows a ** or *** they are
treated as if both a / plus a further * are present. Hence:
setopt GLOBSTARSHORT
ls -ld -- **.c
is equivalent to
ls -ld -- **/*.c
Glob Qualifiers
Patterns used for filename generation may end in a list of qualifiers
enclosed in parentheses. The qualifiers specify which filenames that
otherwise match the given pattern will be inserted in the argument
list.
If the option BARE_GLOB_QUAL is set, then a trailing set of parentheses
containing no `|' or `(' characters (or `~' if it is special) is taken
as a set of glob qualifiers. A glob subexpression that would normally
be taken as glob qualifiers, for example `(^x)', can be forced to be
treated as part of the glob pattern by doubling the parentheses, in
this case producing `((^x))'.
If the option EXTENDED_GLOB is set, a different syntax for glob quali-
fiers is available, namely `(#qx)' where x is any of the same glob
qualifiers used in the other format. The qualifiers must still appear
at the end of the pattern. However, with this syntax multiple glob
qualifiers may be chained together. They are treated as a logical AND
of the individual sets of flags. Also, as the syntax is unambiguous,
the expression will be treated as glob qualifiers just as long any
parentheses contained within it are balanced; appearance of `|', `(' or
`~' does not negate the effect. Note that qualifiers will be recog-
nised in this form even if a bare glob qualifier exists at the end of
the pattern, for example `*(#q*)(.)' will recognise executable regular
files if both options are set; however, mixed syntax should probably be
avoided for the sake of clarity. Note that within conditions using the
`[[' form the presence of a parenthesised expression (#q...) at the end
of a string indicates that globbing should be performed; the expression
may include glob qualifiers, but it is also valid if it is simply (#q).
This does not apply to the right hand side of pattern match operators
as the syntax already has special significance.
A qualifier may be any one of the following:
/ directories
F `full' (i.e. non-empty) directories. Note that the opposite
sense (^F) expands to empty directories and all non-directories.
Use (/^F) for empty directories.
. plain files
@ symbolic links
= sockets
p named pipes (FIFOs)
* executable plain files (0100 or 0010 or 0001)
% device files (character or block special)
%b block special files
%c character special files
r owner-readable files (0400)
w owner-writable files (0200)
x owner-executable files (0100)
A group-readable files (0040)
I group-writable files (0020)
E group-executable files (0010)
R world-readable files (0004)
W world-writable files (0002)
X world-executable files (0001)
s setuid files (04000)
S setgid files (02000)
t files with the sticky bit (01000)
fspec files with access rights matching spec. This spec may be a octal
number optionally preceded by a `=', a `+', or a `-'. If none of
these characters is given, the behavior is the same as for `='.
The octal number describes the mode bits to be expected, if com-
bined with a `=', the value given must match the file-modes ex-
actly, 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 ac-
cess 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 sta-
tus (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 separa-
tor 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 execu-
tion.
During the execution of string the filename currently being
tested is available in the parameter REPLY; the parameter may be
altered to a string to be inserted into the list instead of the
original filename. In addition, the parameter reply may be set
to an array or a string, which overrides the value of REPLY. If
set to an array, the latter is inserted into the command line
word by word.
For example, suppose a directory contains a single file
`lonely'. Then the expression `*(e:'reply=(${REPLY}{1,2})':)'
will cause the words `lonely1' and `lonely2' to be inserted into
the command line. Note the quoting of string.
The form +cmd has the same effect, but no delimiters appear
around cmd. Instead, cmd is taken as the longest sequence of
characters following the + that are alphanumeric or underscore.
Typically cmd will be the name of a shell function that contains
the appropriate test. For example,
nt() { [[ $REPLY -nt $NTREF ]] }
NTREF=reffile
ls -ld -- *(+nt)
lists all files in the directory that have been modified more
recently than reffile.
ddev files on the device dev
l[-|+]ct
files having a link count less than ct (-), greater than ct (+),
or equal to ct
U files owned by the effective user ID
G files owned by the effective group ID
uid files owned by user ID id if that is a number. Otherwise, id
specifies a user name: the character after the `u' will be taken
as a separator and the string between it and the next matching
separator will be taken as a user name. The starting separators
`[', `{', and `<' match the final separators `]', `}', and `>',
respectively; any other character matches itself. The selected
files are those owned by this user. For example, `u:foo:' or
`u[foo]' selects files owned by user `foo'.
gid like uid but with group IDs or names
a[Mwhms][-|+]n
files accessed exactly n days ago. Files accessed within the
last n days are selected using a negative value for n (-n).
Files accessed more than n days ago are selected by a positive n
value (+n). Optional unit specifiers `M', `w', `h', `m' or `s'
(e.g. `ah5') cause the check to be performed with months (of 30
days), weeks, hours, minutes or seconds instead of days, respec-
tively. 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 ac-
cessed 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 in-
ode 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 giga-
bytes, `g' or `G', and terabytes, `t' or `T'.) If a size speci-
fier 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 inclu-
sive. Note also that the set of files "less than" the test size
only includes files that would not match the equality test;
hence `*(Lm-1)' only matches files of zero size.
^ negates all qualifiers following it
- toggles between making the qualifiers work on symbolic links
(the default) and the files they point to, if any; any symbolic
link for whose target the `stat' system call fails (whatever the
cause of the failure) is treated as a file in its own right
M sets the MARK_DIRS option for the current pattern
T appends a trailing qualifier mark to the filenames, analogous to
the LIST_TYPES option, for the current pattern (overrides M)
N sets the NULL_GLOB option for the current pattern
D sets the GLOB_DOTS option for the current pattern
n sets the NUMERIC_GLOB_SORT option for the current pattern
Yn enables short-circuit mode: the pattern will expand to at most n
filenames. If more than n matches exist, only the first n
matches in directory traversal order will be considered.
Implies oN when no oc qualifier is used.
oc specifies how the names of the files should be sorted. The fol-
lowing values of c sort in the following ways:
n By name.
L By the size (length) of the files.
l By number of links.
a By time of last access, youngest first.
m By time of last modification, youngest first.
c By time of last inode change, youngest first.
d By directories: files in subdirectories appear before
those in the current directory at each level of the
search -- this is best combined with other criteria, for
example `odon' to sort on names for files within the same
directory.
N No sorting is performed.
estring
+cmd Sort by shell code (see below).
Note that the modifiers ^ and - are used, so `*(^-oL)' gives a
list of all files sorted by file size in descending order, 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 qual-
ifier 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 re-
turn, 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 num-
ber 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 sub-
scripts. beg and the optional end may be mathematical expres-
sions. As in parameter subscripting they may be negative to make
them count from the last match backward. E.g.: `*(-OL[1,3])'
gives a list of the names of the three largest files.
Pstring
The string will be prepended to each glob match as a separate
word. string is delimited in the same way as arguments to the e
glob qualifier described above. The qualifier can be repeated;
the words are prepended separately so that the resulting command
line contains the words in the same order they were given in the
list of glob qualifiers.
A typical use for this is to prepend an option before all occur-
rences of a file name; for example, the pattern `*(P:-f:)' pro-
duces the command line arguments `-f file1 -f file2 ...'
If the modifier ^ is active, then string will be appended in-
stead of prepended. Prepending and appending is done indepen-
dently so both can be used on the same glob expression; for ex-
ample 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 `Modi-
fiers' in the section `History Expansion'). Each modifier must be in-
troduced by a separate `:'. Note also that the result after modifica-
tion 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 ac-
tual filename generation is performed, although note that the presence
of the parentheses causes the entire expression to be subjected to any
global pattern matching options such as NULL_GLOB. Thus:
ls -ld -- *(-/)
lists all directories and symbolic links that point to directories, and
ls -ld -- *(-@)
lists all broken symbolic links, and
ls -ld -- *(%W)
lists all world-writable device files in the current directory, and
ls -ld -- *(W,X)
lists all files in the current directory that are world-writable or
world-executable, and
print -rC1 /tmp/foo*(u0^@:t)
outputs the basename of all root-owned files beginning with the string
`foo' in /tmp, ignoring symlinks, and
ls -ld -- *.*~(lex|parse).[ch](^D^l1)
lists all files having a link count of one whose names contain a dot
(but not those starting with a dot, since GLOB_DOTS is explicitly
switched off) except for lex.c, lex.h, parse.c and parse.h.
print -rC1 b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/)
demonstrates how colon modifiers and other qualifiers may be chained
together. The ordinary qualifier `.' is applied first, then the colon
modifiers in order from left to right. So if EXTENDED_GLOB is set and
the base pattern matches the regular file builtin.pro, the shell will
print `shmiltin.shmo'.
zsh 5.9 May 14, 2022 ZSHEXPN(1)
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