Regular Expressions/Shell Regular Expressions
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The Unix shell recognises a glob syntax for use with filename substitution. With the extglob extension of ksh and bash, it is equivalent to a basic form of regular expression in expressiveness.
Operator | Effect |
---|---|
? | The hook operator specifies any single character. |
[ ] | boxes enable a single character to be matched against a character lists or character range. |
[! ] | A compliment box enables a single character not within in a character list or character range to be matched. A non-standard equivalent, supported by GNU bash, is the caret syntax [^ ]. |
* | An asterisk specifies zero or more characters to match. |
?(pattern-list) | Matches zero or one occurrence of the given patterns. extglob extension. |
*(pattern-list) | Matches zero or more occurrences of the given patterns. extglob extension. |
+(pattern-list) | Matches one or more occurrences of the given patterns. extglob extension. |
@(pattern-list) | Matches exactly one of the given patterns. extglob extension. |
!(pattern-list) | Matches anything except one of the given patterns. extglob extension. |
Differences from common regular expressions are:
- The asterisk and hook operators mean different things.
- The compliment bow is formed using the exclamation mark (!) in the POSIX standard, not a caret (^). Some shells, such as GNU bash, allow the caret to be used as an extension.
- The extglob extensions are not standard. They are only available in Korn shell (enabled by default) and GNU bash (enabled via
shopt -s extglob
).
Use in Tools
[edit | edit source]Tools and languages that utilize this regular expression syntax include:
- For the general glob syntax, all POSIX "bourne-compatible" shells.
- For the extglob part, Korn shell and bash.