Java Cookbook

Regular Expression Syntax

Problem

You need to learn the syntax of regular expressions.

Solution

Consult Chapter 4 for a list of the regular expression characters that the Apache Regular Expression API matches.

Table 4-2. Regular expression syntax

Subexpression	Will match:	Notes
General
a	The letter a (and similarly for any other Unicode character not listed in this table)
^	Start of line/string
$	End of line/string
.	Any one character
[...]	“Character class”; any one character from those listed
[^...]	Any one character not from those listed
Normal (greedy) multipliers (“greedy closures”)
{m,n}	Multiplier (closure) for from m to n repetitions
{m,}	Multiplier for from m repetitions on up
{,n}	Multiplier for 0 up to n repetitions
*	Multiplier for 0 or more repetitions	Short for {0,}
+	Multiplier for 1 or more repetitions	Short for {1,}
?	Multiplier for 0 or 1 repetitions	Short for {0,1}
Reluctant (non-greedy) multipliers (“reluctant closures”)
*?	Reluctant multiplier: 0 or more
+?	Reluctant multiplier: 1 or more
??	Reluctant multiplier: 0 or 1 times
Alternation and grouping
( )	Grouping
|	Alternation
Escapes and shorthands
\	Escape character: turns metacharacters off, and turns following alphabetics (t, w, d, and s) into metacharacters.
\t	Tab character
\w	Character in a word	Use \w+ for a word
\d	Numeric digit	Use \d+ for a number ...