Regular expression quick start guide
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Revision as of 11:08, 19 October 2011 by Luc Morissette (Talk | contribs)
Quick Reference Table
| Regular Expression Pattern | Explanations | Examples |
|---|---|---|
| Meta characters [\^$.|?*+( |
Special caracters used in regex.
|
|
|
Literal characters |
All characters (except the metacharacters) match a single instance of themselves.
|
/a/ matches "a" |
| [characters] |
Character classes or character set. A character class matches a single character out of all the possibilities offered by the character class. |
/[0-9]/ matches a single digit |
| [\d] |
Shorthand character classes matching digits. Same as [0-9]. |
/[\d]/ matches a single digit |
| . |
Dot matches any characters. |
/a.c/ matches both "a4c" and "ayc" |
| ^ | Matches at the start of the string the regex pattern is applied to. Matches a position rather than a character. | |
| $ | Matches at the end of the string the regex pattern is applied to. Matches a position rather than a character. | |
| {m,n} |
Matches at least “m” and at most “n” occurrences of preceeding character, character class or group. |
|
| * | Matches zero or more occurrences of preceeding character, character class or group. | |
| + | Matches one or more occurrences of preceeding character, character class or group. |
|
| ? | Matches zero or one occurrences of preceeding character, character class or group. | |
| () | Parentheses are used for group or capturing group |
|
| \0, \1, \2, ... | Substitute the value matched by the nth grouped sub-expression, used in remapped fields. | |
Examples
Here are some examples:
Add 2720 prefix:
/^(\d+)$/2720\1/
or
/^([0-9]*)$/2720\1/
Strip first 4 digits:
/^([0-9]{4})([0-9]*)$/\2/
Strip # and 7 first digits:
/^([#])([0-9]{7})([0-9]*)$/\3/
Web Online Tools
- Regular builder tool : www.gskinner.com/RegExr
- Ruby regular expression editor and tester : rubular.com
- Ruby regular expression editor and tester with replace : http://lumadis.be/regex/test_regex.php
References
