Regular expression quick start guide

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Revision as of 14:44, 27 January 2010

Quick Reference Table

Regular Expression Pattern	Explanations	Examples
Meta characters [\^$.\|?*+(	Special caracters used in regex. Must be escape with backslash "\" to use a literal characters.
Literal characters	All characters (except the metacharacters) match a single instance of themselves. { and } are literal characters, unless they're part of a valid regular expression token (e.g. the {n} quantifier).	/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.

Quick References

Text Patterns and Matches

A regular expression, or regex for short, is a pattern describing a certain amount of text.

Metacharacters

Literal Characters

Character Classes or Character Sets

Shorthand Character Classes

The Dot Matches (Almost) Any Character

Repetition

Optional

Anchors

Alternation

Grouping and Capturing Group

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

@@ Line 29: / Line 29: @@
 | ''/[0-9]/'' matches a single digit<br>
 |-
 | [\d]<br>
 | Shorthand character classes matching digits. Same as [0-9].<br>
 | ''/[\d]/'' matches a single digit<br>
 |-
 | .<br>
 | Dot matches any characters.<br>
 | ''/a.c/'' matches both "a4c" and "ayc"'''<br>'''
 |-
 | ^
 | Matches at the start of the string the regex pattern is applied to. Matches a position rather than a character.
 | <br>
 |-
 | $
 | Matches at the end of the string the regex pattern is applied to. Matches a position rather than a character.
 | <br>
 |-
 | {m,n}<br>
 | Matches at least “m” and at most “n” occurrences of preceeding character, character class or group.<br>
 | <br>
 |-
@@ Line 54: / Line 54: @@
 |-
 | +
 | Matches '''one '''or '''more '''occurrences of preceeding character, character class or group.'''<br>'''
 | <br>
 |-
-| ?
+| &nbsp;?
 | Matches '''zero '''or '''one '''occurrences of&nbsp; preceeding character, character class or group.
 | <br>
 |-
 | ()
 | Parentheses are used for group or capturing group<br>
 | <br>
 |-
@@ Line 76: / Line 76: @@
 === Text Patterns and Matches<br>  ===
-<br>
+A regular expression, or regex for short, is a pattern describing a certain amount of text.<br>
 === Metacharacters  ===
 === Literal Characters<br>  ===