Regular expression: Difference between revisions
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'''Regular expressions''', also referred to as regex or regexp, provide a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters. In the UNL<sup>arium</sup> framework, regular expressions follow the [http://www.pcre.org/ PCRE library] and must be provided between / /. They are used mainly to enhance the power of [[ | '''Regular expressions''', also referred to as regex or regexp, provide a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters. In the UNL<sup>arium</sup> framework, regular expressions follow the [http://www.pcre.org/ PCRE library] and must be provided between / /. They are used mainly to enhance the power of [[L-rule]]s. | ||
== Main features == | == Main features == | ||
{|border=1 cellpadding=2 align=center | {|border=1 cellpadding=2 align=center | ||
Revision as of 16:41, 26 March 2010
Regular expressions, also referred to as regex or regexp, provide a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters. In the UNLarium framework, regular expressions follow the PCRE library and must be provided between / /. They are used mainly to enhance the power of L-rules.
Main features
| Characters | |
|---|---|
| a | match the character a |
| 3 | match the number 3 |
| Wildcards | |
| . | match any character |
| \… | quote single metacharacter: \. matches a dot instead of any character and \\ matches a single backslash |
| \w | alphanumeric + underscore (shortcut for [0-9a-zA-Z_]) |
| \W | any character not covered by \w |
| \d | numeric (shortcut for [0-9]) |
| \D | any character not covered by \d |
| \s | whitespace (shortcut for [ \t\n\r\f]) |
| \S | any character not covered by \s |
| […] | any character listed: [a5!d-g] means a, 5, ! and d, e, f, g |
| [^…] | any character not listed: [^a5!d-g] means anything but a, 5, ! and d, e, f, g |
| Quantifiers | |
| ? | match 1 or 0 times |
| * | 0 or more times |
| + | 1 or more times |
| {n} | exactly n times |
| {n,} | at least n times |
| {n,m} | at least n but not more than m times, as often as possible |
| Grouping | |
| (...) | |
Examples
| RegEx | Description | Matches |
|---|---|---|
| /abc/ | match the sequence "abc" | abc |
| /abc./ | match the sequence "abc" plus one character | abca, abcb, abcc, abcd, abce, ... |
| /abc(a)?/ | match the sequence "abc" plus zero or one character "a" | abc, abca |
| /abc(a)*/ | match the sequence "abc" plus zero or more characters "a" | abc, abca, abcaa, abcaaa, abcaaaa, abcaaaaa, |
| /abc(a)+/ | match the sequence "abc" plus one or more characters "a" | abca, abcaa, abcaaa, abcaaaa, ... |
| /abc(a){3}/ | match the sequence "abc" plus three characters "a" | abcaaa |
| /abc(a)(3,}/ | match the sequence "abc" plus at least three characters "a" | abcaaa, abcaaaa, abcaaaaa, abcaaaaaa, ... |
| /abc(a)(2,5}/ | match the sequence "abc" plus two to five characters "a" | abcaa, abcaaa, abcaaaa, abcaaaaa |
| /a[bcd]e/ | match "a" plus "b", "c" or "d", plus "e" | abe, ace, ade |
| /a[^bcd]e/ | match "a" plus any character that is not "b", "c" or "d", plus "e" | aae, aee, afe, age, ahe, ... |
| /a\d/ | match "a" plus any single digit | a0, a1, a2, a3, a4, a5, a6, a7, a8, a9 |
| /a(\d){2}/ | match "a" plus any two digits | a00, a01, a02, a03, a04, ... |
