Regular expression
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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 UNLarium framework, regular expressions follow the PCRE library.
Syntax
Regular expressions come between /forward slashes/. They are used to replace "/strings/" (between quotes), [/natural language entries/] (between brackets), [[/UWs/]] (between double square brackets) or /features/. For instance:
- "/.../" matches any string made of three characters
- [/[abc]/] matches the natural language entries "a", "b" and "c"
- [[/(abc|def)/]] matches the UW "abc" or "def"
- /(MCL|FEM)/ matches the features MCL or FEM
Metacharacters
For a comprehensive list of metacharacters, please consult Perl Compatible Regular Expressions.
| 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 | |
| (...) | |
| Special characters | |
| { } [ ] ( ) ^ $ . | * + ? | to match these characters, override (escape) with \ |
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, ... |
