Patterns and pattern matching

FIXME missing better extglob description; missing shell options to control matching, e.g. nocalseglob etc..

A pattern is a string description. Bash can use it in various situations:

Pathname expansion (Globbing - matching filenames)
Pattern matching in conditional expressions
Substring removal and search and replace in Parameter Expansion
Pattern-based branching using the case command

The pattern description language is relatively easy. Any character that's not mentioned below matches itself. The NUL character may not occur in a pattern. If special characters are quoted, they're matched literally without their special meaning.

Normal pattern language

Sequence	Description
`*`	Matches any string, including the null string (empty string)
`?`	Matches any single character
`X`	Matches the character `X` which can be any character that has no special meaning
`\X`	Matches the character `X`, where the character's special meaning is taken away using the backslash
`\\`	Matches a backslash
`[...]`	Defines a pattern bracket expression (see below). Matches any of the enclosed characters at this position.

Bracket expressions

The bracket expression [...] mentioned above has some useful specialities:

Bracket expression	Description
`[XYZ]`	The "normal" bracket expression, matching either `X`, `Y` or `Z`
`[X-Z]`	A range expression: Matching all the characters from `X` to `Y` (whatever that means in your current locale, it depends how the characters are sorted!)
`[[:class:]]`	Matches all the characters defined by a POSIX® character class: `alnum`, `alpha`, `ascii`, `blank`, `cntrl`, `digit`, `graph`, `lower`, `print`, `punct`, `space`, `upper`, `word` and `xdigit`
`[^...]`	A negating expression: It matches all the characters that are not in the bracket expression
`[!...]`	Equivalent to `[^...]`
`[]...]` or `[-...]`	Used to include the characters `]` and `-` into the set, they need to be the first characters after the opening bracket
`[=C=]`	Matches any character that is eqivalent to the collation weight of `C` (current locale!)
`[[.SYMBOL.]]`	Matches the collating symbol `SYMBOL`

Examples

Some simple examples using normal pattern matching:

Pattern "Hello world" matches
- Hello world
Pattern [Hh]"ello world" matches
- ⇒ Hello world
- ⇒ hello world
Pattern Hello* matches (for example)
- ⇒ Hello world
- ⇒ Helloworld
- ⇒ HelloWoRlD
- ⇒ Hello
Pattern Hello world[[:punct:]] matches (for example)
- ⇒ Hello world!
- ⇒ Hello world.
- ⇒ Hello world+
- ⇒ Hello world?
Pattern [[.backslash.]]Hello[[.vertical-line.]]world[[.exclamation-mark.]] matches (using collation sybols)
- ⇒ \Hello|world!

Extended pattern language

If you set the shell option extglob, Bash understands some more powerful patterns. Here, a <PATTERN-LIST> is one or more pattern, separated by the pipe-symbol (|).

`?(<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

Examples

Delete all but one specific file

rm -f !(survivior.txt)

Pattern matching configuration

Related shell options

option	classification	description
`dotglob`	globbing	see Pathname expansion customization
`extglob`	global	enable/disable extended pattern matching language, as described above
`failglob`	globbing	see Pathname expansion customization
`nocaseglob`	globbing	see Pathname expansion customization
`nocasematch`	pattern/string matching	perform pattern matching without regarding the case of individual letters
`nullglob`	globbing	see Pathname expansion customization