<<TableOfContents>>

= Globs =
"Glob" is the common name for a set of Bash features that match or expand specific types of patterns.  Some synonyms for globbing (depending on the context in which it appears) are [[http://tiswww.case.edu/php/chet/bash/bashref.html#Pattern-Matching|pattern matching]], pattern expansion, filename expansion, and so on.  A glob may look like {{{*.txt}}} and, when used to match filenames, is sometimes called a "wildcard".

Traditional shell globs use a very simple syntax, which is less expressive than a RegularExpression.  Most characters in a glob are treated literally, but a {{{*}}} matches 0 or more characters, a {{{?}}} matches precisely one character, and {{{[...]}}} matches any single character in a specified set (see [[#Ranges|Ranges]] below).  All globs are implicitly anchored at both start and end.  For example:
||`*` ||Matches any string, of any length ||
||`foo*` ||Matches any string beginning with `foo` ||
||`*x*` ||Matches any string containing an `x` (beginning, middle or end) ||
||`*.tar.gz` ||Matches any string ending with `.tar.gz` ||
||`*.[ch]` ||Matches any string ending with `.c` or `.h` ||
||`foo?` ||Matches `foot` or `foo$` but not `fools` ||




Bash expands globs which appear unquoted in commands, by matching filenames relative to the current directory.  The expansion of the glob results in 1 or more words (0 or more, if certain options are set), and those words (filenames) are used in the command.  For example:

{{{#!highlight bash
tar xvf *.tar
# Expands to: tar xvf file1.tar file2.tar file42.tar ...
# (which is generally not what one wants)
}}}
Even if a file contains internal whitespace, the expansion of a glob that matches that file will still preserve each filename as a single word.  For example,

{{{#!highlight bash
# This is safe even if a filename contains whitespace:
for f in *.tar; do
    tar tvf "$f"
done

# But this one is not:
for f in $(ls | grep '\.tar$'); do
    tar tvf "$f"
done
}}}
In the second example above, the output of {{{ls}}} is filtered, and then the result of the whole pipeline is [[WordSplitting|divided into words]], to serve as iterative values for the loop.  This word-splitting will occur at internal whitespace within each filename, which makes it useless in the general case.  The first example has no such problem, because the filenames produced by the glob do ''not'' undergo any further word-splitting.  For more such examples, see BashPitfalls.

A glob that ends in `/` will only match directories (the `/` will be included in the results):

{{{#!highlight bash
touch file1 file2
mkdir dir1 dir2

printf '<%s>' *; printf '\n'
# <dir1><dir2><file1><file2>
printf '<%s>' */; printf '\n'
# <dir1/><dir2/>
}}}

Globs are also used to match patterns in a few places in Bash.  The most traditional is in the [[BashGuide/TestsAndConditionals#Choices|case]] command:

{{{#!highlight bash
case "$input" in
    [Yy]|'') confirm=1;;
    [Nn]*) confirm=0;;
    *) echo "I don't understand.  Please try again.";;
esac
}}}
Patterns (which are separated by {{{|}}} characters) are matched against the first word after the {{{case}}} itself.  The first pattern which matches, "wins", causing the corresponding commands to be executed.

Bash also allows globs to appear on the right-hand side of a comparison inside a {{{[[}}} command:

{{{#!highlight bash
if [[ $output = *[Ee]rror* ]]; then ...
}}}
Finally, globs are used during [[BashFAQ/073|parameter expansion]] to indicate patterns which may be stripped out, or replaced, during a substitution.  Simple examples (there are many more on the previously referenced page):

{{{#!highlight bash
filename=${path##*/}    # strip leading pattern that matches */ (be greedy)
dirname=${path%/*}      # strip trailing pattern matching /* (non-greedy)

printf '%s\n' "${arr[@]}"          # dump an array, one element per line
printf '%s\n' "${arr[@]/error*/}"  # dump array, removing error* if matched
}}}
(Reference: [[BashGuide/Arrays|Arrays]] [[Quotes]] [[http://wiki.bash-hackers.org/commands/builtin/printf|printf]].)

== Ranges ==
Globs can specify a ''range'' or ''class'' of characters, using square brackets.  This gives you the ability to match against a set of characters.  For example:
||`[abcd]` ||Matches `a` or `b` or `c` or `d` ||
||`[a-d]` ||The same as above, if ''globasciiranges'' is set or your [[locale]] is C or POSIX. Otherwise, implementation-defined. ||
||`[!aeiouAEIOU]` ||Matches any character ''except'' `a`, `e`, `i`, `o`, `u` and their uppercase counterparts ||
||`[[:alnum:]]` ||Matches any alphanumeric character in the current locale (letter or number) ||
||`[[:space:]]` ||Matches any whitespace character ||
||`[![:space:]]` ||Matches any character that is ''not'' whitespace ||
||`[[:digit:]_.]` ||Matches any digit, or `_` or `.` ||




In most shell implementations, one may also use `^` as the range negation character, e.g. `[^[:space:]]`.  However, POSIX specifies `!` for this role, and therefore `!` is the standard choice.

=== globasciiranges (since bash 4.3-alpha) ===
Interprets [a-d] as [abcd]. To match a literal -, include it as first or last character.

=== For older versions ===
Note that ''Implementation-defined'' means it may work as you expect on one machine, but give completely different results on another machine.  Do not use the `m-n` syntax unless you have explicitly set your locale to C first, or you may get unexpected results.  The [[http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_03_05|POSIX character class expressions]] should be preferred whenever possible.

== Options which change globbing behavior ==
=== extglob ===
In addition to the traditional globs (supported by all Bourne-family shells) that we've seen so far, Bash (and Korn Shell) offers ''extended globs'', which have the expressive power of [[RegularExpression|regular expressions]].  Korn shell enables these by default; in Bash, you must run the command

{{{#!highlight bash
shopt -s extglob
}}}
in your shell (or at the ''start'' of your script -- see note on parsing below) to use them.  The [[http://tiswww.case.edu/php/chet/bash/bashref.html#SEC36|pattern matching reference]] describes the syntax, which is reproduced here:

 ?(pattern-list):: Matches zero or one occurrence of the given patterns.
 *(pattern-list):: Matches zero or more occurrences of the given patterns.
 +(pattern-list):: Matches one or more occurrences of the given patterns.
 @(pattern-list):: Matches one of the given patterns.
 !(pattern-list):: Matches anything except one of the given patterns.

Patterns in a list are separated by `|` characters.

Extended globs allow you to solve a number of problems which otherwise require a rather surprising amount of ugly hacking; for example,

{{{#!highlight bash
# To remove all the files except ones matching *.jpg:
rm !(*.jpg)
# All except *.jpg and *.gif and *.png:
rm !(*.jpg|*.gif|*.png)
}}}
{{{#!highlight bash
# To copy all the MP3 songs except one to your device
cp !(04*).mp3 /mnt
}}}
To use an extglob in a parameter expansion (this can also be done in one BASH statement with [[BashFAQ/067|read]]):

{{{#!highlight bash
# To trim leading and trailing whitespace from a variable
x=${x##+([[:space:]])}; x=${x%%+([[:space:]])}
}}}
Extended glob patterns can be nested, too.

{{{#!highlight bash
[[ $fruit = @(ba*(na)|a+(p)le) ]] && echo "Nice fruit"
}}}
'''`extglob` changes the way certain characters are parsed. It is necessary to have a newline (not just a semicolon) between `shopt -s extglob` and any subsequent commands to use it.''' You cannot enable extended globs inside a [[BashGuide/CompoundCommands#Command.2BAFw_Grouping|group command]] that uses them, because the entire block is parsed before the `shopt` is ''evaluated''.  Note that the typical [[BashGuide/CompoundCommands#Functions|function]] body ''is'' a ''group command''. An unpleasant workaround could be to use a ''subshell command list'' as the function body.

Therefore, if you use this option in a script, it is best put right under the shebang line.

{{{#!highlight bash
#!/usr/bin/env bash
shopt -s extglob   # and others, such as nullglob dotglob
}}}
If your code must be sourced and needs `extglob`, ensure it preserves the original setting from your shell:

{{{#!highlight bash
# remember whether extglob was originally set, so we know whether to unset it
shopt -q extglob; extglob_set=$?
# set extglob if it wasn't originally set.
((extglob_set)) && shopt -s extglob
# Note, 0 (true) from shopt -q is "false" in a math context.

# The basic concept behind the following is to delay parsing of the globs until evaluation.
# This matters at group commands, such as functions in { } blocks

declare -a s='( !(x) )'
echo "${s[@]}"

echo "${InvalidVar:-!(x)}"

eval 'echo !(x)'  # using eval if no other option.

# unset extglob if it wasn't originally set
((extglob_set)) && shopt -u extglob
}}}
This should also apply for other shell options.

=== nullglob ===
`nullglob` expands non-matching globs to zero arguments, rather than to themselves.

{{{#!highlight bash
$ ls *.c
ls: cannot access *.c: No such file or directory

# with nullglob set
shopt -s nullglob
ls *.c
# Runs "ls" with no arguments, and lists EVERYTHING
}}}
Typically, `nullglob` is used to [[BashFAQ/004|count the number of files]] matching a pattern:

{{{#!highlight bash
shopt -s nullglob
files=(*)
echo "There are ${#files[@]} files in this directory."
}}}
Without `nullglob`, the glob would expand to a literal `*` in an empty directory, resulting in an erroneous count of 1.

It can also be used to iterate the matches of a glob with a `for` loop.

{{{#!highlight bash
shopt -s nullglob
for f in ./*.mp4; do
    command1 "$f"
    command2 "$f"
done
}}}
Without `nullglob`, if there were no matches for {{{./*.mp4}}}, the loop would be still run once with {{{f='./*.mp4'}}}.

==== Warning ====
Enabling `nullglob` on a wide scope can trigger bugs caused by bad programming practices. It "breaks" the expectations of many utilities.

Removing array elements:

{{{#!highlight bash
shopt -s nullglob
unset array[1]
#unsets nothing
unset -v "array[1]"
#correct
}}}
Array member assignments in compound form using subscripts:

{{{#!highlight bash
shopt -s nullglob
array=([1]=*)
#results in an empty array
}}}
This was reported as a [[http://lists.gnu.org/archive/html/bug-bash/2012-08/msg00032.html|bug]] in 2012, yet is unchanged to this day.

  EDIT: It has been changed in bash4.3; now, it results in an array that only contains {{{array[1]='*'}}}.

Apart from few builtins that use modified parsing under special conditions (e.g. declare) '''always use [[Quotes]]''' when arguments to simple commands could be interpreted as globs.

Enabling `failglob`, `nullglob`, or both during development and testing can help catch mistakes early. To prevent ''pathname expansion'' occuring in unintended places, you can set [[#failglob|failglob]]. However, you must then guarantee all intended globs match at least one file. Also note that the result of a glob expansion does not always differ from the glob itself. `failglob` won't distinguish `echo ?` from `echo '?'` in a directory containing only a file named `?`. `nullglob` will.

==== Portability ====
"null globbing" is not specified by POSIX. In portable scripts, you must explicitly check that a glob match was successful by checking that the files actually exist.

{{{#!highlight bash
# POSIX

for x in *; do
    [ -e "$x" ] || break
    ...
done

f() {
    [ -e "$1" ] || return 1

    for x do
        ...
    done
}

f * || echo "No files found"
}}}
Some modern POSIX-compatible shells allow null globbing as an extension.

{{{#!highlight bash
# Bash
shopt -s nullglob
}}}
In ksh93, there is no toggle-able option. Rather, that the "nullglob" behavior is to be enabled is specified inline using the "N" option to the `∼()` sub-pattern syntax.

{{{#!highlight bash
# ksh93

for x in ~(N)*; do
    ...
done
}}}
In zsh, a toggle-able option (NULL_GLOB) or a glob qualifier(N) can be used.

{{{#!highlight bash
# zsh
for x in *(N); do ...; done # or setopt NULL_GLOB
}}}
mksh doesn't yet support nullglob (maintainer says he'll think about it).

=== dotglob ===
By convention, a filename beginning with a dot is "hidden", and not shown by `ls`.  Globbing uses the same convention -- filenames beginning with a dot are not matched by a glob, unless the glob also begins with a dot.  Bash has a '''dotglob''' option that lets globs match "dot files":

{{{#!highlight bash
shopt -s dotglob nullglob
files=(*)
echo "There are ${#files[@]} files here, including dot files and subdirs"
}}}
It should be noted that when `dotglob` is enabled, `*` will match files like `.bashrc` but ''not'' the `.` or `..` directories.  This is orthogonal to the problem of matching "just the dot files" (prior to bash 5.2; see '''globskipdots''' below) -- a glob of `.*` ''will'' match `.` and `..`, typically causing problems.

=== globskipdots (since bash 5.2) ===
When '''globskipdots''' is on, pathname expansion will never expand to `.` or `..`.

{{{#!highlight bash
LC_COLLATE=C
shopt -s extglob nullglob

touch .a ..b ...c ....d ......

# with globskipdots on
declare -p files=( .* )            # filenames that start with "."
# declare -a files=([0]="......" [1]="....d" [2]="...c" [3]="..b" [4]=".a")
declare -p files=( ..* )           # filenames that start with ".."
# declare -a files=([0]="......" [1]="....d" [2]="...c" [3]="..b")
declare -p files=( +(..)?([!.]*) ) # filenames that start with an even number of "."
# declare -a files=([0]="......" [1]="....d" [2]="..b")

# with globskipdots off
shopt -u globskipdots
declare -p files=( .* )            # filenames that start with "."
# declare -a files=([0]="." [1]=".." [2]="......" [3]="....d" [4]="...c" [5]="..b" [6]=".a")
declare -p files=( ..* )           # filenames that start with ".."
# declare -a files=([0]=".." [1]="......" [2]="....d" [3]="...c" [4]="..b")
declare -p files=( +(..)?([!.]*) ) # filenames that start with an even number of "."
# declare -a files=([0]=".." [1]="......" [2]="....d" [3]="..b")
}}}

This option is enabled by default; before bash 5.2, pathname expansion behaved as if '''globskipdots''' was disabled.

=== globstar (since bash 4.0-alpha) ===
globstar recursively repeats a pattern containing `**`.

{{{#!highlight bash
$ shopt -s globstar; tree
.
├── directory2
│   ├── directory3
│   ├── file1.c
│   └── file2
├── file1
└── file2.c

# Suppose that for the following examples.
}}}
Matching files:

{{{#!highlight bash
$ files=(**)
# equivalent to: files=(* */* */*/*)
# finds all files recursively

$ files=(**/*.c)
# equivalent to: files=(*.c */*.c */*/*.c)
# finds all *.c files recursively
# corresponds to: find -name "*.c"
# Caveat: **.c will not work, it is equivalent to *.c
}}}
Just like '*', '**' followed by a '/' will only match directories:

{{{#!highlight bash
$ files=(**/)
# finds all subdirectories

$ files=(. **/)
# finds all subdirectories, including the current directory
# corresponds to: find -type d
}}}
=== failglob ===
If a pattern fails to match, bash reports an expansion error. This can be useful at the commandline:

{{{#!highlight bash
# Good at the command line!
$ > *.foo # creates file '*.foo' if glob fails to match
$ shopt -s failglob
$ > *.foo # doesn't get executed
-bash: no match: *.foo
}}}
=== GLOBIGNORE ===
The Bash variable (not shopt) `GLOBIGNORE` allows you to specify patterns a glob ''should not'' match.  This lets you work around the infamous "I want to match all of my dot files, but not . or .." problem:

{{{#!highlight bash
$ echo .*
. .. .bash_history .bash_logout .bashrc .inputrc .vimrc
$ GLOBIGNORE=.:..
$ echo .*
.bash_history .bash_logout .bashrc .inputrc .vimrc
}}}
Unset GLOBIGNORE

{{{#!highlight bash
$ GLOBIGNORE=
$ echo .*
. .. .bash_history .bash_logout .bashrc .inputrc .vimrc
}}}
=== nocasematch ===
Globs inside [[ and case commands are matched case-insensitive:

{{{#!highlight bash
foo() {
   local f r=0 nc=0
   shopt -q nocasematch && nc=1 || shopt -s nocasematch
   for f; do
      [[ $f = *.@(txt|jpg) ]] || continue
      cmd -on "$f" || r=1
   done
   ((nc)) || shopt -u nocasematch
   return $r
}
}}}
This is conventionally done this way:

{{{#!highlight bash
case $f in
    *.[Tt][Xx][Tt]|*.[Jj][Pp][Gg]) : ;;
    *) continue
esac
}}}
and in earlier versions of bash we'd use a similar glob:

{{{#!highlight bash
[[ $f = *.@([Tt][Xx][Tt]|[Jj][Pp][Gg]) ]] || continue
}}}
or with no extglob:

{{{#!highlight bash
[[ $f = *.[Tt][Xx][Tt] ]] || [[ $f = *.[Jj][Pp][Gg] ]] || continue
}}}
Here, one might keep the tests separate for maintenance; they can be easily reused and dropped,

 . without having to concern oneself with where they fit in relation to an internal ||.

Note also:

{{{#!highlight bash
[[ $f = *.@([Tt][Xx][Tt]|[Jj][Pp]?([Ee])[Gg]) ]]
}}}
Variants left as an exercise.

=== nocaseglob (since bash 2.02-alpha1) ===
This option makes ''pathname expansion'' case-insensitive. In contrast, [[#nocasematch|nocasematch]] operates on matches in ''[[BashGuide/TestsAndConditionals#Conditional_Blocks|[[]]'' and ''[[BashGuide/TestsAndConditionals#Choices|case]]'' commands.

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CategoryShell