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 argu-
ment, any of the five steps that are needed are performed one af-
ter 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 file-
name expansion is performed immediately after alias expansion,
preceding the set of five expansions mentioned above.
Filename Generation
This expansion, commonly referred to as globbing, is always done
last.
The following sections explain the types of expansion in detail.
HISTORY EXPANSION
History expansion allows you to use words from previous command lines in
the command line you are typing. This simplifies spelling corrections
and the repetition of complicated commands or arguments.
Immediately before execution, each command is saved in the history list,
the size of which is controlled by the HISTSIZE parameter. The one most
recent command is always retained in any case. Each saved command in
the history list is called a history event and is assigned a number, be-
ginning with 1 (one) when the shell starts up. The history number that
you may see in your prompt (see EXPANSION OF PROMPT SEQUENCES in zsh-
misc(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 pa-
rameter, which is `!' by default, and may occur anywhere on the command
line, including inside double quotes (but not inside single quotes '...'
or C-style quotes $'...' nor when escaped with a backslash).
The first character is followed by an optional event designator (see the
section `Event Designators') and then an optional word designator (the
section `Word Designators'); if neither of these designators is present,
no history expansion occurs.
Input lines containing history expansions are echoed after being ex-
panded, but before any other expansions take place and before the com-
mand is executed. It is this expanded form that is recorded as the his-
tory event for later references.
History expansions do not nest.
By default, a history reference with no event designator refers to the
same event as any preceding history reference on that command line; if
it is the only history reference in a command, it refers to the previous
command. However, if the option CSH_JUNKIE_HISTORY is set, then every
history reference with no event specification always refers to the pre-
vious command.
For example, `!' is the event designator for the previous command, so
`!!:1' always refers to the first word of the previous command, and
`!!$' 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, respec-
tively, of the same event referenced by the nearest other history refer-
ence preceding them on the current command line, or to the previous com-
mand 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 para-
meter.
! 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 refer-
ence with no event designator (see the section `Overview').
!! Refer to the previous command. By itself, this expansion repeats
the previous command.
!n Refer to command-line n.
!-n Refer to the current command-line minus n.
!str Refer to the most recent command starting with str.
!?str[?]
Refer to the most recent command containing str. The trailing
`?' is necessary if this reference is to be followed by a 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 des-
ignators 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 di-
rectory, 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 function
to resolve symbolic links.
Note: on systems that do not have a realpath(3) library function,
symbolic links are not resolved, so on those systems `a' and `A'
are equivalent.
Note: foo:A and realpath(foo) are different on some inputs. For
realpath(foo) semantics, see the `P` modifier.
c Resolve a command name into an absolute path by searching the
command path given by the PATH variable. This does not work for
commands containing directory parts. Note also that this does
not usually work as a glob qualifier unless a file of the same
name is found in the current directory.
e Remove all but the part of the filename extension following the
`.'; see the definition of the filename extension in the descrip-
tion of the r modifier below. Note that according to that defin-
ition the result will be empty if the string ends with a `.'.
h [ digits ]
Remove a trailing pathname component, shortening the path by one
directory level: this is the `head' of the pathname. This works
like `dirname'. If the h is followed immediately (with no spaces
or other separator) by any number of decimal digits, and the
value of the resulting number is non-zero, that number of leading
components is preserved instead of the final component being re-
moved. In an absolute path the leading `/' is the first compo-
nent, 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 expan-
sion).
l Convert the words to all lowercase.
p Print the new command but do not execute it. Only works with
history expansion.
P Turn a file name into an absolute path, like realpath(3). The
resulting path will be absolute, will refer to the same directory
entry as the input filename, and none of its components will be
symbolic links or equal to `.' or `..'.
Unlike realpath(3), non-existent trailing components are 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 components is
preserved instead of the default 1; 0 is treated the same as 1.
u Convert the words to all uppercase.
x Like q, but break into words at whitespace. Does not work with
parameter expansion.
The s/l/r/ substitution works as follows. By default the left-hand side
of substitutions are not patterns, but character strings. Any character
can be used as the delimiter in place of `/'. A backslash quotes the
delimiter character. The character `&', in the right-hand-side r, is
replaced by the text from the left-hand-side l. The `&' can be quoted
with a backslash. A null l uses the previous string either from the
previous l or from the contextual scan string s from `!?s'. You can
omit the rightmost delimiter if a newline immediately follows r; the
rightmost `?' in a context scan can similarly be omitted. Note the same
record of the last l and r is maintained across all forms of expansion.
Note that if a `&' is used within glob qualifiers an extra backslash is
needed as a & is a special character in this case.
Also note that the order of expansions affects the interpretation of l
and r. When used in a history expansion, which occurs before any other
expansions, l and r are treated as literal strings (except as explained
for HIST_SUBST_PATTERN below). When used in parameter expansion, the
replacement of r into the parameter's value is done first, and then any
additional process, parameter, command, arithmetic, or brace references
are applied, which may evaluate those substitutions and expansions more
than once if l appears more than once in the starting value. When used
in a glob qualifier, any substitutions or expansions are performed once
at the time the qualifier is parsed, even before the `:s' expression it-
self 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, how-
ever, 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 compli-
cated patterns used in globbing qualifiers may need the extended glob
qualifier notation (#q:s/.../.../) in order for the shell to recognize
the expression as a glob qualifier. Further, note that bad patterns in
the substitution are not subject to the NO_BAD_PATTERN option so will
cause an error.
When HIST_SUBST_PATTERN is set, l may start with a # to indicate that
the pattern must match at the start of the string to be substituted, and
a % may appear at the start or after an # to indicate that the pattern
must match at the end of the string to be substituted. The % or # may
be quoted with two backslashes.
For example, the following piece of filename generation code with the
EXTENDED_GLOB option:
print -r -- *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/)
takes the expansion of *.c and applies the glob qualifiers in the
(#q...) expression, which consists of a substitution modifier anchored
to the start and end of each word (#%). This turns on backreferences
((#b)), so that the parenthesised subexpression is available in the 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 expansion
and filename generation. They are listed here to provide a single point
of reference for all modifiers.
f Repeats the immediately (without a colon) following modifier un-
til the resulting word doesn't change any more.
F:expr:
Like f, but repeats only n times if the expression expr evaluates
to n. Any character can be used instead of the `:'; if `(', `[',
or `{' is used as the opening delimiter, the closing delimiter
should be ')', `]', or `}', respectively.
w Makes the immediately following modifier work on each word in the
string.
W:sep: Like w but words are considered to be the parts of the string
that are separated by sep. Any character can be used instead of
the `:'; opening parentheses are handled specially, see above.
PROCESS SUBSTITUTION
Each part of a command argument that takes the form `<(list)', `>(list)'
or `=(list)' is subject to process substitution. The expression may be
preceded or followed by other strings except that, to prevent clashes
with commonly occurring strings and patterns, the last form must occur
at the start of a command argument, and the forms are only expanded when
first parsing command or assignment arguments. Process substitutions
may be used following redirection operators; in this case, the substitu-
tion 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 system
supports the /dev/fd mechanism, the command argument is the name of the
device file corresponding to a file descriptor; otherwise, if the system
supports named pipes (FIFOs), the command argument will be a named pipe.
If the form with > is selected then writing on this special file will
provide input for list. If < is used, then the file passed as an argu-
ment will be connected to the output of the list process. For example,
paste <(cut -f1 file1) <(cut -f3 file2) |
tee >(process1) >(process2) >/dev/null
cuts fields 1 and 3 from the files file1 and file2 respectively, pastes
the results together, and sends it to the processes process1 and
process2.
If =(...) is used instead of <(...), then the file passed as an argument
will be the name of a temporary file containing the output of the list
process. This may be used instead of the < form for a program that ex-
pects 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 con-
tents.
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 security
reasons such as when the programme is running setuid. In the second
case, if the programme does not actually open the file, the subshell at-
tempting to read from or write to the pipe will (in a typical implemen-
tation, different operating systems may have different behaviour) block
for ever and have to be killed explicitly. In both cases, the shell ac-
tually supplies the information using a pipe, so that programmes that
expect to lseek (see lseek(2)) on the file will not work.
Also note that the previous example can be more compactly and 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 fin-
ish and hence an immediately following command cannot rely on the re-
sults 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 ap-
propriate 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 func-
tion 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
$scalar substitutes a single word `only word'. Note that second element
of array was elided. Scalar parameters can be elided too if their value
is null (empty). To avoid elision, use quoting as follows: "$scalar"
for scalars and "${array[@]}" or "${(@)array}" for arrays. (The last
two forms are equivalent.)
Parameter expansions can involve flags, as in `${(@kv)aliases}', and
other operators, such as `${PREFIX:-"/usr/local"}'. Parameter 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 parame-
ter expansion, command substitution, and arithmetic expansion. In addi-
tion to the following operations, the colon modifiers described in the
section `Modifiers' in the section `History Expansion' can be applied:
for example, ${i:s/foo/bar/} performs string substitution on the expan-
sion 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 subscript
or any colon modifiers appearing after the name, or any of the
characters `^', `=', `~', `#' or `+' appearing before the name,
all of which work with or without braces.
If name is an array parameter, and the KSH_ARRAYS option is not
set, then the value of each element of name is substituted, one
element per word. Otherwise, the expansion results in one word
only; with KSH_ARRAYS, this is the first element of an array. No
field splitting is done on the result unless the SH_WORD_SPLIT
option is set. See also the flags = and s:string:.
${+name}
If name is the name of a set parameter `1' is substituted, other-
wise `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 substitution
is not quoted, or if the `(@)' flag or the name[@] syntax is used,
matching and replacement is performed on each array element separately.
${name#pattern}
${name##pattern}
If the pattern matches the beginning of the value of name, then
substitute the value of name with the matched portion deleted;
otherwise, just substitute the value of name. In the first form,
the smallest matching pattern is preferred; in the second form,
the largest matching pattern is preferred.
${name%pattern}
${name%%pattern}
If the pattern matches the end of the value of name, then substi-
tute the value of name with the matched portion deleted; other-
wise, 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 ${a:^b}
will output `1 a 2 b'. For `:^^', then the input is repeated un-
til all of the longer array has been used up and the above will
output `1 a 2 b 3 a 4 b'.
Either or both inputs may be a scalar, they will be treated as an
array of length 1 with the scalar as the only element. If either
array is empty, the other array is output with no extra elements
inserted.
Currently the following code will output `a b' and `1' as two
separate elements, which can be unexpected. The second print pro-
vides a workaround which should continue to work if this is
changed.
a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}"
${name:offset}
${name:offset:length}
This syntax gives effects similar to parameter subscripting in
the form $name[start,end], but is compatible with other shells;
note that both offset and length are interpreted differently from
the components of a subscript.
If offset is non-negative, then if the variable name is a scalar
substitute the contents starting offset characters from the first
character of the string, and if name is an array substitute ele-
ments 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 ar-
ray (this is different from native zsh subscript notation).
Hence 0 refers to the first character or element regardless of
the setting of the option KSH_ARRAYS.
A negative offset counts backwards from the end of the scalar or
array, so that -1 corresponds to the last character or element,
and so on.
When positive, length counts from the offset position toward the
end of the scalar or array. When negative, length counts back
from the end. If this results in a position smaller than offset,
a diagnostic is printed and nothing is substituted.
The option MULTIBYTE is obeyed, i.e. the offset and length count
multibyte characters where appropriate.
offset and length undergo the same set of shell substitutions as
for scalar assignment; in addition, they are then subject to
arithmetic evaluation. Hence, for example
print ${foo:3}
print ${foo: 1 + 2}
print ${foo:$(( 1 + 2))}
print ${foo:$(echo 1 + 2)}
all have the same effect, extracting the string starting at the
fourth character of $foo if the substitution would otherwise re-
turn a scalar, or the array starting at the fourth element if
$foo would return an array. Note that with the option KSH_ARRAYS
$foo always returns a scalar (regardless of the use of the offset
syntax) and a form such as ${foo[*]:3} is required to extract el-
ements 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. In-
stead, a space may be inserted before the -. Furthermore, nei-
ther offset nor length may begin with an alphabetic character or
& as these are used to indicate history-style modifiers. To sub-
stitute a value from a variable, the recommended approach is to
precede it with a $ as this signifies the intention (parameter
substitution can easily be rendered unreadable); however, as
arithmetic substitution is performed, the expression ${var: offs}
does work, retrieving the offset from $offs.
For further compatibility with other shells there is a special
case for array offset 0. This usually accesses the first element
of the array. However, if the substitution refers to the posi-
tional 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 spe-
cially unless either the option GLOB_SUBST is set, or $opat is
instead substituted as ${~opat}.
The pattern may begin with a `#', in which case the pattern must
match at the start of the string, or `%', in which case it must
match at the end of the string, or `#%' in which case the pattern
must match the entire string. The repl may be an empty string,
in which case the final `/' may also be omitted. To quote the
final `/' in other cases it should be preceded by a single back-
slash; this is not necessary if the `/' occurs inside a substi-
tuted parameter. Note also that the `#', `%' and `#% are not ac-
tive 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 ef-
fect 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 result
is `spy spy lispy star'.
${#spec}
If spec is one of the above substitutions, substitute the length
in characters of the result instead of the result itself. If
spec is an array expression, substitute the number of elements of
the result. This has the side-effect that joining is skipped
even in quoted forms, which may affect other sub-expressions in
spec. Note that `^', `=', and `~', below, must appear to the
left of `#' when these forms are combined.
If the option POSIX_IDENTIFIERS is not set, and spec is a simple
name, then the braces are optional; this is true even for special
parameters so e.g. $#- and $#* take the length of the string $-
and the array $* respectively. If POSIX_IDENTIFIERS is set, then
braces are required for the # to be treated in this fashion.
${^spec}
${^^spec}
Turn on the RC_EXPAND_PARAM option for the evaluation of spec; if
the `^' is doubled, turn it off. When this option is set, array
expansions of the form foo${xx}bar, where the parameter xx is set
to (a b c), are substituted with `fooabar foobbar foocbar' in-
stead 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 them-
selves 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 affects
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 surrounding
pattern operation on the result may cancel it. Hence, for exam-
ple, if the parameter foo is set to *, ${~foo//\*/*.c} is substi-
tuted by the pattern *.c, which may be expanded by filename gen-
eration, but ${${~foo}//\*/*.c} substitutes to the string *.c,
which will not be further expanded.
If a ${...} type parameter expression or a $(...) type command substitu-
tion is used in place of name above, it is expanded first and the result
is used as if it were the value of name. Thus it is possible to perform
nested operations: ${${foo#head}%tail} substitutes the value of $foo
with both `head' and `tail' deleted. The form with $(...) is often use-
ful in combination with the flags described next; see the examples be-
low. Each name or nested ${...} in a parameter expansion may also be
followed by a subscript expression as described in Array Parameters in
zshparam(1).
Note that double quotes may appear around nested expressions, in which
case only the part inside is treated as quoted; for example,
${(f)"$(foo)"} quotes the result of $(foo), but the flag `(f)' (see be-
low) is applied using the rules for unquoted expansions. Note further
that quotes are themselves nested in this context; for example, in
"${(@f)"$(foo)"}", there are two sets of quotes, one surrounding the
whole expression, the other (redundant) surrounding the $(foo) as be-
fore.
Parameter Expansion Flags
If the opening brace is directly followed by an opening parenthesis, the
string up to the matching closing parenthesis will be taken as a list of
flags. In cases where repeating a flag is meaningful, the repetitions
need not be consecutive; for example, `(q%q%q)' means the same thing as
the more readable `(%%qqq)'. The following flags are supported:
# Evaluate the resulting words as numeric expressions and interpret
these as character codes. Output the corresponding characters.
Note that this form is entirely distinct from use of the # with-
out parentheses.
If the MULTIBYTE option is set and the number is greater than 127
(i.e. not an ASCII character) it is treated as a Unicode charac-
ter.
% Expand all % escapes in the resulting words in the same way as in
prompts (see EXPANSION OF PROMPT SEQUENCES in zshmisc(1)). If
this flag is given twice, full prompt expansion is done on the
resulting words, depending on the setting of the PROMPT_PERCENT,
PROMPT_SUBST and PROMPT_BANG options.
@ In double quotes, array elements are put into separate words.
E.g., `"${(@)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 `${...::=...}'. If this flag is repeated (as in `AA'), as-
signs an associative array parameter. Assignment is made before
sorting or padding; if field splitting is active, the word part
is split before assignment. The name part may be a subscripted
range for ordinary arrays; when assigning an associative array,
the word part must be converted to an array, for example by using
`${(AA)=name=...}' to activate field splitting.
Surrounding context such as additional nesting or use of the
value in a scalar assignment may cause the array to be joined
back into a single string again.
a Sort in array index order; when combined with `O' sort in reverse
array index order. Note that `a' is therefore equivalent to the
default but `Oa' is useful for obtaining an array's elements in
reverse order.
b Quote with backslashes only characters that are special to 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-alphanumer-
ics, 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 expansion,
command substitution and arithmetic expansion, on the result.
Such expansions can be nested but too deep recursion may have un-
predictable 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 (ele-
ment 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. How-
ever, this flag may not be combined with subscript ranges. With
the KSH_ARRAYS option a subscript `[*]' or `[@]' is needed to op-
erate 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 charac-
ters 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 inte-
ger. 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 lo-
cale 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 para-
meter name. It is an error if this nested substitution produces
an array with more than one word. For example, if `name=assoc'
where the parameter assoc is an associative array, then
`${${(P)name}[elt]}' refers to the element of the associative
subscripted `elt'.
q Quote characters that are special to the shell in the resulting
words with backslashes; unprintable or invalid characters are
quoted using the $'\NNN' form, with separate quotes for each
octet.
If this flag is given twice, the resulting words are quoted in
single quotes and if it is given three times, the words are
quoted in double quotes; in these forms no special handling of
unprintable or invalid characters is attempted. If the flag is
given four times, the words are quoted in single quotes preceded
by a $. Note that in all three of these forms quoting is done
unconditionally, even if this does not change the way the result-
ing string would be interpreted by the shell.
If a q- is given (only a single q may appear), a minimal form of
single quoting is used that only quotes the string if needed to
protect special characters. Typically this form gives the most
readable output.
If a q+ is given, an extended form of minimal quoting is used
that causes unprintable characters to be rendered using $'...'.
This quoting is similar to that used by the output of values by
the typeset family of commands.
Q Remove one level of quotes from the resulting words.
t Use a string describing the type of the parameter where the value
of the parameter would usually appear. This string consists of
keywords separated by hyphens (`-'). The first keyword in the
string describes the main type, it can be one of `scalar', `ar-
ray', `integer', `float' or `association'. The other keywords de-
scribe the type in more detail:
local for local parameters
left for left justified parameters
right_blanks
for right justified parameters with leading blanks
right_zeros
for right justified parameters with leading zeros
lower for parameters whose value is converted to all lower case
when it is expanded
upper for parameters whose value is converted to all upper case
when it is expanded
readonly
for readonly parameters
tag for tagged parameters
tied for parameters tied to another parameter in the manner of
PATH (colon-separated list) and path (array), whether
these are special parameters or user-defined with `typeset
-T'
export for exported parameters
unique for arrays which keep only the first occurrence of 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 op-
tions)
Note that this is done very late, even later than the `(s)' flag.
So to access single words in the result use nested expansions as
in `${${(z)foo}[2]}'. Likewise, to remove the quotes in the re-
sulting words use `${(Q)${(z)foo}}'.
0 Split the result of the expansion on null bytes. This is a
shorthand for `ps:\0:'.
The following flags (except p) are followed by one or more arguments as
shown. Any character, or the matching pairs `(...)', `{...}', `[...]',
or `<...>', may be used in place of a colon as delimiters, but note that
when a flag takes more than one argument, a matched pair of delimiters
must surround each argument.
p Recognize the same escape sequences as the print builtin in
string arguments to any of the flags described below that follow
this argument.
Alternatively, with this option string arguments may be in the
form $var in which case the value of the variable is substituted.
Note this form is strict; the string argument does not undergo
general parameter expansion.
For example,
sep=:
val=a:b:c
print ${(ps.$sep.)val}
splits the variable on a :.
~ Strings inserted into the expansion by any of the flags below are
to be treated as patterns. This applies to the string arguments
of flags that follow ~ within the same set of parentheses. Com-
pare with ~ outside parentheses, which forces the entire substi-
tuted 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 truncated
if required and placed in a field expr characters wide.
The arguments :string1: and :string2: are optional; neither, the
first, or both may be given. Note that the same pairs of 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 certain
Asian character sets and certain special effects use wider char-
acters; combining characters have zero width. Non-printable
characters are arbitrarily counted as zero width; how they would
actually be displayed will vary.
If the m is repeated, the character either counts zero (if it has
zero width), else one. For printable character strings this has
the effect of counting the number of glyphs (visibly separate
characters), except for the case where combining characters them-
selves 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 padding is ap-
plied 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 ele-
ments 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 unquoted
comment character is a comment.
(Z+C+) causes comments to be parsed and removed. The rule for
comments is standard: anything between a word starting
with the third character of $HISTCHARS, default #, up to
the next newline is a comment.
(Z+n+) causes unquoted newlines to be treated as ordinary white-
space, else they are treated as if they are shell code de-
limiters 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
longest match should be replaced:
% str="abab"
% echo ${str/*b/_}
_
% echo ${(S)str/*b/_}
_ab
%
I:expr:
Search the exprth match (where expr evaluates to a number). This
only applies when searching for substrings, either with the S
flag, or with ${.../...} (only the exprth match is substituted)
or ${...//...} (all matches from the exprth on are substituted).
The default is to take the first match.
The exprth match is counted such that there is either one or zero
matches from each starting position in the string, although for
global substitution matches overlapping previous replacements are
ignored. With the ${...%...} and ${...%%...} forms, the starting
position for the match moves backwards from the end as the index
increases, while with the other forms it moves forward from the
start.
Hence with the string
which switch is the right switch for Ipswich?
substitutions of the form ${(SI:N:)string#w*ch} as N increases
from 1 will match and remove `which', `witch', `witch' and
`wich'; the form using `##' will match and remove `which switch
is the right switch for Ipswich', `witch is the right switch for
Ipswich', `witch for Ipswich' and `wich'. The form using `%' will
remove the same matches as for `#', but in reverse order, and the
form using `%%' will remove the same matches as for `##' in re-
verse 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 per-
formed from the inside outwards. At each level, the substitution
takes account of whether the current value is a scalar or an ar-
ray, whether the whole substitution is in double quotes, and what
flags are supplied to the current level of substitution, just as
if the nested substitution were the outermost. The flags are not
propagated up to enclosing substitutions; the nested substitution
will return either a scalar or an array as determined by the
flags, possibly adjusted for quoting. All the following steps
take place where applicable at all levels of substitution.
Note that, unless the `(P)' flag is present, the flags and any
subscripts apply directly to the value of the nested 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 expansion
and filename expansion (i.e. leading ~ and =). Thus, for exam-
ple, ${${:-=cat}:h} expands to the directory where the cat pro-
gram resides. (Explanation: the internal substitution has no pa-
rameter but a default value =cat, which is expanded by filename
expansion to a full path; the outer substitution then applies the
modifier :h and takes the directory part of the path.)
2. Internal parameter flags
Any parameter flags set by one of the typeset family of commands,
in particular the -L, -R, -Z, -u and -l options for padding and
capitalization, are applied directly to the parameter value.
Note these flags are options to the command, e.g. `typeset -Z';
they are not the same as the flags used within parameter substi-
tutions.
At the outermost level of substitution, the `(P)' flag (rule 4.)
ignores these transformations and uses the unmodified value of
the parameter as the name to be replaced. This is usually the
desired behavior because padding may make the value syntactically
illegal as a parameter name, but if capitalization changes are
desired, use the ${${(P)foo}} form (rule 25.).
3. Parameter subscripting
If the value is a raw parameter reference with a subscript, such
as ${var[3]}, the effect of subscripting is applied directly to
the parameter. Subscripts are evaluated left to right; 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 result
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 substitution
appears in double quotes, and neither an `(@)' flag nor a `#'
length operator is present at the current level, then words of
the value are joined with the first character of the parameter
$IFS, by default a space, between each word (single word arrays
are not modified). If the `(j)' flag is present, that is used
for joining instead of $IFS.
6. Nested subscripting
Any remaining subscripts (i.e. of a nested substitution) are
evaluated at this point, based on whether the value is an array
or a scalar. As with 3., multiple subscripts can appear. Note
that ${foo[2,4][2]} is thus equivalent to ${${foo[2,4]}[2]} and
also to "${${(@)foo[2,4]}[2]}" (the nested substitution returns
an array in both cases), but not to "${${foo[2,4]}[2]}" (the
nested substitution returns a scalar because of the quotes).
7. Modifiers
Any modifiers, as specified by a trailing `#', `%', `/' (possibly
doubled) or by a set of modifiers of the form `:...' (see the
section `Modifiers' in the section `History Expansion'), are ap-
plied 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 together
using the given string or the first character of $IFS if none.
Note that the `(F)' flag implicitly supplies a string for joining
in this manner.
11. Simple word splitting
If one of the `(s)' or `(f)' flags are present, or the `=' speci-
fier was present (e.g. ${=var}), the word is split on occurrences
of the specified string, or (for = with neither of the two flags
present) any of the characters in $IFS.
If no `(s)', `(f)' or `=' was given, but the word is not quoted
and the option SH_WORD_SPLIT is set, the word is split on 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 ap-
plied.
14. Quote application
Any quoting or unquoting using `(q)' and `(Q)' and related flags
is applied.
15. Directory naming
Any directory name substitution using `(D)' flag is applied.
16. Visibility enhancement
Any modifications to make characters visible using the `(V)' flag
are applied.
17. Lexical word splitting
If the '(z)' flag or one of the forms of the '(Z)' flag is
present, the word is split as if it were a shell command line, so
that quotation marks and other metacharacters are used to decide
what constitutes a word. Note this form of splitting is entirely
distinct from that described by rule 11.: it does not use $IFS,
and does not cause forced joining.
18. Uniqueness
If the result is an array and the `(u)' flag was present, dupli-
cate elements are removed from the array.
19. Ordering
If the result is still an array and one of the `(o)' or `(O)'
flags was present, the array is reordered.
20. RC_EXPAND_PARAM
At this point the decision is made whether any resulting array
elements are to be combined element by element with surrounding
text, as given by either the RC_EXPAND_PARAM option or the `^'
flag.
21. Re-evaluation
Any `(e)' flag is applied to the value, forcing it to be re-exam-
ined for new parameter substitutions, but also for command and
arithmetic substitutions.
22. Padding
Any padding of the value by the `(l.fill.)' or `(r.fill.)' flags
is applied.
23. Semantic joining
In contexts where expansion semantics requires a single word to
result, all words are rejoined with the first character of IFS
between. So in `${(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 result-
ing zero-length argument, whether from a scalar or an element of
an array, is elided from the list of arguments inserted into the
command line.
Strictly speaking, the removal happens later as the same happens
with other forms of substitution; the point to note here is 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. Compare this
with the effect of $(<file) alone, which divides the file up by words,
or the same inside double quotes, which makes the entire content of the
file a single string.
The following illustrates the rules for nested parameter expansions.
Suppose that $foo contains the array (bar baz):
"${(@)${foo}[1]}"
This produces the result b. First, the inner substitution
"${foo}", which has no array (@) flag, produces a single word re-
sult "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 substi-
tution 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 sub-
stitution, including the special form just mentioned, is eligible for
filename generation.
ARITHMETIC EXPANSION
A string of the form `$[exp]' or `$((exp))' is substituted with the
value of the arithmetic expression exp. exp is subjected to parameter
expansion, command substitution and arithmetic expansion before it is
evaluated. See the section `Arithmetic Evaluation'.
BRACE EXPANSION
A string of the form `foo{xx,yy,zz}bar' is expanded to the individual
words `fooxxbar', `fooyybar' and `foozzbar'. Left-to-right order is
preserved. This construct may be nested. Commas may be quoted in order
to include them literally in a word.
An expression of the form `{n1..n2}', where n1 and n2 are integers, is
expanded to every number between n1 and n2 inclusive. If either number
begins with a zero, all the resulting numbers will be padded with lead-
ing zeroes to that minimum width, but for negative numbers the - charac-
ter is also included in the width. If the numbers are in decreasing or-
der the resulting sequence will also be in decreasing order.
An expression of the form `{n1..n2..n3}', where n1, n2, and n3 are inte-
gers, is expanded as above, but only every n3th number starting from n1
is output. If n3 is negative the numbers are output in reverse order,
this is slightly different from simply swapping n1 and n2 in the case
that the step n3 doesn't evenly divide the range. Zero padding can be
specified in any of the three numbers, specifying it in the third can be
useful to pad for example `{-99..100..01}' which is not possible to
specify by putting a 0 on either of the first two numbers (i.e. pad to
two characters).
An expression of the form `{c1..c2}', where c1 and c2 are single charac-
ters (which may be multibyte characters), is expanded to every character
in the range from c1 to c2 in whatever character sequence is used inter-
nally. For characters with code points below 128 this is US ASCII (this
is the only case most users will need). If any intervening character is
not printable, appropriate quotation is used to render it printable. If
the character sequence is reversed, the output is in reverse order, e.g.
`{d..a}' is substituted as `d c b a'.
If a brace expression matches none of the above forms, it is left un-
changed, unless the option BRACE_CCL (an abbreviation for `brace charac-
ter class') is set. In that case, it is expanded to a list of the indi-
vidual characters between the braces sorted into the order of the char-
acters in the ASCII character set (multibyte characters are not cur-
rently handled). The syntax is similar to a [...] expression in file-
name generation: `-' is treated specially to denote a range of charac-
ters, but `^' or `!' as the first character is treated normally. For
example, `{abcdef0-9}' expands to 16 words 0 1 2 3 4 5 6 7 8 9 a b c d e
f.
Note that brace expansion is not part of filename generation (globbing);
an expression such as */{foo,bar} is split into two separate words */foo
and */bar before filename generation takes place. In particular, note
that this is liable to produce a `no match' error if either of the two
expressions does not match; this is to be contrasted with */(foo|bar),
which is treated as a single pattern but otherwise has similar effects.
To combine brace expansion with array expansion, see the ${^spec} form
described in the section `Parameter Expansion' above.
FILENAME EXPANSION
Each word is checked to see if it begins with an unquoted `~'. If it
does, then the word up to a `/', or the end of the word if there is no
`/', is checked to see if it can be substituted in one of the ways 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 position
in the directory stack. `~0' is equivalent to `~+', and `~1' is the top
of the stack. `~+' followed by a number is replaced by the directory at
that position in the directory stack. `~+0' is equivalent to `~+', and
`~+1' is the top of the stack. `~-' followed by a number is replaced by
the directory that many positions from the bottom of the stack. `~-0'
is the bottom of the stack. The PUSHD_MINUS option exchanges the ef-
fects of `~+' and `~-' where they are followed by a number.
Dynamic named directories
If the function zsh_directory_name exists, or the shell variable zsh_di-
rectory_name_functions exists and contains an array of function names,
then the functions are used to implement dynamic directory naming. The
functions are tried in order until one returns status zero, so it is im-
portant that functions test whether they can handle the case in question
and return an appropriate status.
A `~' followed by a string namstr in unquoted square brackets is treated
specially as a dynamic directory name. Note that the first unquoted
closing square bracket always terminates namstr. The shell function is
passed two arguments: the string n (for name) and namstr. It should ei-
ther set the array reply to a single element which is the directory cor-
responding 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 direc-
tory; 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 expan-
sion 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 ef-
fective.
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 di-
rectories 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 di-
rectory 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 fam-
ily. In this case, the right hand side will be treated as a colon-sepa-
rated list in the manner of the PATH parameter, so that a `~' or an `='
following a `:' is eligible for expansion. All such behaviour can be
disabled by quoting the `~', the `=', or the whole expression (but not
simply the colon); the EQUALS option is also respected.
If the option MAGIC_EQUAL_SUBST is set, any unquoted shell argument in
the form `identifier=expression' becomes eligible for file expansion as
described in the previous paragraph. Quoting the first `=' also 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; otherwise
they are not treated specially by the shell.
The word is replaced with a list of sorted filenames that match the pat-
tern. If no matching pattern is found, the shell gives an error mes-
sage, unless the NULL_GLOB option is set, in which case the word is
deleted; or unless the NOMATCH option is unset, in which case the word
is left unchanged.
In filename generation, the character `/' must be matched explicitly;
also, a `.' must be matched explicitly at the beginning of a pattern or
after a `/', unless the GLOB_DOTS option is set. No filename generation
pattern matches the files `.' or `..'. In other instances of pattern
matching, the `/' and `.' are not treated specially.
Glob Operators
* Matches any string, including the null string.
? Matches any character.
[...] Matches any of the enclosed characters. Ranges of characters can
be specified by separating two characters by a `-'. A `-' or `]'
may be matched by including it as the first character in the
list. There are also several named classes of characters, in the
form `[:name:]' with the following meanings. The first set use
the macros provided by the operating system to test for the given
character combinations, including any modifications due to local
language settings, see ctype(3):
[:alnum:]
The character is alphanumeric
[:alpha:]
The character is alphabetic
[:ascii:]
The character is 7-bit, i.e. is a single-byte character
without the top bit set.
[:blank:]
The character is a blank character
[:cntrl:]
The character is a control character
[:digit:]
The character is a decimal digit
[:graph:]
The character is a printable character other than 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 charac-
ter. Note that there may be a sequence of more than one
bytes that taken together form the prefix of a multibyte
character. To test for a potentially incomplete byte se-
quence, use the pattern `[[:INCOMPLETE:]]*'. This will
never match a sequence starting with a valid multibyte
character.
[:INVALID:]
Matches a byte that does not start a valid multibyte char-
acter. Note this may be a continuation byte of an incom-
plete multibyte character as any part of a multibyte
string consisting of invalid and incomplete multibyte
characters is treated as single bytes.
[:WORD:]
The character is treated as part of a word; this test is
sensitive to the value of the WORDCHARS parameter
Note that the square brackets are additional to those enclosing
the whole set of characters, so to test for a single alphanumeric
character you need `[[:alnum:]]'. Named character sets can be
used alongside other types, e.g. `[[:alpha:]0-9]'.
[^...]
[!...] Like [...], except that it matches any character which is not in
the given set.
<[x]-[y]>
Matches any number in the range x to y, inclusive. Either of the
numbers may be omitted to make the range open-ended; hence `<->'
matches any number. To match individual digits, the [...] form
is more efficient.
Be careful when using other wildcards adjacent to patterns of
this form; for example, <0-9>* will actually match any number
whatsoever at the start of the string, since the `<0-9>' will
match the first digit, and the `*' will match any others. This
is a trap for the unwary, but is in fact an inevitable 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 `!' immedi-
ately 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 pat-
terns 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 re-
peated; this includes an empty string, a pattern already followed
by `##', or parentheses when part of a KSH_GLOB pattern (for ex-
ample, `!(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 re-
cursive 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 ex-
ample, in case statements and tests within `[[...]]'), a `/' is not spe-
cial; and `/' is also not special after a `~' appearing outside paren-
theses 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 begin-
ning of the matched parentheses in the array $mbegin, and the in-
dices of the end in the array $mend, with the first element of
each array 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 substitution,
such as ${param//pat/repl}, only the data for the last match re-
mains available. In the case of global replacements this may
still be useful. See the example for the m flag below.
The numbering of backreferences strictly follows the order of the
opening parentheses from left to right in the pattern string, al-
though 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 fol-
lowed by # and matched zero times -- then the matched string is
set to the empty string, and the start and end indices are set to
-1.
Pattern matching with backreferences is slightly slower than
without.
B Deactivate backreferences, negating the effect of the b flag from
that point on.
cN,M The flag (#cN,M) can be used anywhere that the # or ## operators
can be used except in the expressions `(*/)#' and `(*/)##' in
filename generation, where `/' has special meaning; it cannot be
combined with other globbing flags and a bad pattern error occurs
if it is misplaced. It is equivalent to the form {N,M} in regu-
lar expressions. The previous character or group is required to
match between N and M times, inclusive. The form (#cN) requires
exactly N matches; (#c,M) is equivalent to specifying N as 0;
(#cN,) specifies that there is no maximum limit on the number of
matches.
m Set references to the match data for the entire string matched;
this is similar to backreferencing and does not work in filename
generation. The flag must be in effect at the end of the 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, printing
`vEldt jynx grImps wAqf zhO bUck'.
Unlike backreferences, there is no speed penalty for using match
references, other than the extra substitutions required for the
replacement strings in cases such as the example shown.
M Deactivate the m flag, hence no references to match data will be
created.
anum Approximate matching: num errors are allowed in the string
matched by the pattern. The rules for this are described in the
next subsection.
s, e Unlike the other flags, these have only a local effect, and each
must appear on its own: `(#s)' and `(#e)' are the only valid
forms. The `(#s)' flag succeeds only at the start of the test
string, and the `(#e)' flag succeeds only at the end of the test
string; they correspond to `^' and `$' in standard regular ex-
pressions. They are useful for matching path segments in pat-
terns other than those in filename generation (where path seg-
ments are in any case treated separately). For example,
`*((#s)|/)test((#e)|/)*' matches a path segment `test' in any of
the following strings: test, test/at/start, at/end/test,
in/test/middle.
Another use is in parameter substitution; for example `${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 in-
tended to support the use of glob qualifiers, see below. The re-
sult is that the pattern `(#b)(*).c(#q.)' can be used both for
globbing and for matching against a string. In the former case,
the `(#q.)' will be treated as a glob qualifier and the `(#b)'
will not be useful, while in the latter case the `(#b)' is useful
for backreferences and the `(#q.)' will be ignored. Note that
colon modifiers in the glob qualifiers are also not applied in
ordinary pattern matching.
u Respect the current locale in determining the presence of 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 sepa-
rately. 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, be-
cause 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 approx-
imate match. It is best to place the (#a1) after any path segments
which are known to be correct.
Recursive Globbing
A pathname component of the form `(foo/)#' matches a path consisting of
zero or more directories matching the pattern foo.
As a shorthand, `**/' is equivalent to `(*/)#'; note that this therefore
matches files in the current directory as well as subdirectories. Thus:
ls -ld -- (*/)#bar
or
ls -ld -- **/bar
does a recursive directory search for files named `bar' (potentially in-
cluding 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 qual-
ifiers used in the other format. The qualifiers must still appear at
the end of the pattern. However, with this syntax multiple glob quali-
fiers may be chained together. They are treated as a logical AND of the
individual sets of flags. Also, as the syntax is unambiguous, the ex-
pression will be treated as glob qualifiers just as long any parentheses
contained within it are balanced; appearance of `|', `(' or `~' does not
negate the effect. Note that qualifiers will be recognised in this form
even if a bare glob qualifier exists at the end of the pattern, for ex-
ample `*(#q*)(.)' will recognise executable regular files if both op-
tions 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 syn-
tax 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 charac-
ters specify which access rights are to be checked. If a `u' is
given, those for the owner of the file are used, if a `g' is
given, those of the group are checked, a `o' means to test those
of other users, and the `a' says to test all three groups. The
`=', `+', and `-' again says how the modes are to be checked and
have the same meaning as described for the first form above. The
second list of characters finally says which access rights are to
be expected: `r' for read access, `w' for write access, `x' for
the right to execute the file (or to search a directory), `s' for
the setuid and setgid bits, and `t' for the sticky bit.
Thus, `*(f70?)' gives the files for which the owner has read,
write, and execute permission, and for which other group members
have no rights, independent of the permissions for other users.
The pattern `*(f-100)' gives all files for which the owner does
not have execute permission, and `*(f:gu+w,o-rx:)' gives the
files for which the owner and the other members of the group have
at least write permission, and for which other users don't have
read or execute permission.
estring
+cmd The string will be executed as shell code. The filename will be
included in the list if and only if the code returns a zero 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 separator
will be taken as the string; `[', `{', and `<' match `]', `}',
and `>', respectively, while any other character matches itself.
Note that expansions must be quoted in the string to prevent them
from being expanded before globbing is done. string is then exe-
cuted as shell code. The string globqual is appended to the ar-
ray zsh_eval_context the duration of execution.
During the execution of string the filename currently being
tested is available in the parameter REPLY; the parameter may be
altered to a string to be inserted into the list instead of the
original filename. In addition, the parameter reply may be set
to an array or a string, which overrides the value of REPLY. If
set to an array, the latter is inserted into the command line
word by word.
For example, suppose a directory contains a single file `lonely'.
Then the expression `*(e:'reply=(${REPLY}{1,2})':)' will cause
the words `lonely1' and `lonely2' to be inserted into the command
line. Note the quoting of string.
The form +cmd has the same effect, but no delimiters appear
around cmd. Instead, cmd is taken as the longest sequence of
characters following the + that are alphanumeric or underscore.
Typically cmd will be the name of a shell function that contains
the appropriate test. For example,
nt() { [[ $REPLY -nt $NTREF ]] }
NTREF=reffile
ls -ld -- *(+nt)
lists all files in the directory that have been modified more re-
cently 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 com-
parison. For instance, `echo *(ah-5)' would echo files accessed
within the last five hours, while `echo *(ah+5)' would echo files
accessed at least six hours ago, as times strictly between five
and six hours are treated as five hours.
m[Mwhms][-|+]n
like the file access qualifier, except that it uses the file mod-
ification 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 gigabytes,
`g' or `G', and terabytes, `t' or `T'.) If a size specifier is
used a file is regarded as "exactly" the size if the file size
rounded up to the next unit is equal to the test size. Hence
`*(Lm1)' matches files from 1 byte up to 1 Megabyte inclusive.
Note also that the set of files "less than" the test size only
includes files that would not match the equality test; hence
`*(Lm-1)' only matches files of zero size.
^ negates all qualifiers following it
- toggles between making the qualifiers work on symbolic links (the
default) and the files they point to, if any; any symbolic link
for whose target the `stat' system call fails (whatever the cause
of the failure) is treated as a file in its own right
M sets the MARK_DIRS option for the current pattern
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 direc-
tory.
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 quali-
fier respectively (see above). The code is executed for each
matched file with the parameter REPLY set to the name of the file
on entry and globsort appended to zsh_eval_context. The code
should modify the parameter REPLY in some fashion. On return,
the value of the parameter is used instead of the file name as
the string on which to sort. Unlike other sort operators, oe and
o+ may be repeated, but note that the maximum number of sort op-
erators 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 instead
of prepended. Prepending and appending is done independently so
both can be used on the same glob expression; for example by
writing `*(P:foo:^P:bar:^P:baz:)' which produces the command line
arguments `foo baz file1 bar ...'
More than one of these lists can be combined, separated by commas. The
whole list matches if at least one of the sublists matches (they are
`or'ed, the qualifiers in the sublists are `and'ed). Some qualifiers,
however, affect all matches generated, independent of the sublist in
which they are given. These are the qualifiers `M', `T', `N', `D', `n',
`o', `O' and the subscripts given in brackets (`[...]').
If a `:' appears in a qualifier list, the remainder of the expression in
parenthesis is interpreted as a modifier (see the section `Modifiers' in
the section `History Expansion'). Each modifier must be introduced by a
separate `:'. Note also that the result after modification does not
have to be an existing file. The name of any existing file can be fol-
lowed by a modifier of the form `(:...)' even if no actual filename gen-
eration 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 to-
gether. 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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