Regular Expression Syntax

Special characters

Characters	Description	Matches
.	Not newline	Any character except line terminators (LF, CR, LS, PS).
\t	Tab (HT)	A horizontal tab character (same as \u0009).
\n	Newline (LF)	A newline (line feed) character (same as \u000A).
\v	Vertical tab (VT)	A vertical tab character (same as \u000B).
\f	Form feed (FF)	A form feed character (same as \u000C).
\r	Carriage return (CR)	A carriage return character (same as \u000D).
\cletter	Control code	A control code character whose code unit value is the same as the remainder of dividing the code unit value of letter by 32. For example, \ca is the same as \u0001, \cb the same as \u0002, and so on.
\xhh	ASCII character	A character whose code unit value has an hex value equivalent to the two hex digits hh. For example, \x4c is the same as L, or \x23 the same as #.
\uhhhh	Unicode character	A character whose code unit value has an hex value equivalent to the four hex digits hhhh.
\0	Null	A null character (same as \u0000).
\int	Backreference	The result of the submatch whose opening parenthesis is the int-th (int shall begin by a digit other than 0). See groups below for more info.
\d	Digit	A decimal digit character (same as [[:digit:]]).
\D	Not digit	Any character that is not a decimal digit character (same as [^[:digit]]).
\s	Whitespace	A whitespace character (same as [[:space:]]).
\S	Not whitespace	Any character that is not a whitespace character (same as [^[:space:]]).
\w	Word	An alphanumeric character (same as [[:alnum:]]).
\W	Not word	Any character that is not an alphanumeric character (same as [^[:alnum:]]).
\character	Character	The character character as it is, without interpreting its special meaning within a regex expression. Any character can be escaped except those which form any of the special character sequences above. Needed for: ^ $ \ . * + ? ( ) [ ] { } \|
[class]	Character class	The target character is part of the class
[^class]	Negated character class	The target character is not part of the class

Quantifiers

Quantifiers follow a character or a special pattern character. They can modify the amount of times that character is repeated in the match:

Characters	Times	Effects
*	0 or more	The preceding atom is matched 0 or more times.
+	1 or more	The preceding atom is matched 1 or more times.
?	0 or 1	The preceding atom is optional (matched either 0 times or once).
{int}	int	The preceding atom is matched exactly int times.
{int,}	int or more	The preceding atom is matched int or more times.
{min,max}	Between min and max	The preceding atom is matched at least min times, but not more than max.

By default, all these quantifiers are greedy (that is, they take as many characters that meet the condition as possible). This behavior can be overridden to ungreedy (that is, take as few characters that meet the condition as possible) by adding a question mark (?) after the quantifier.

Assertions

Assertions are conditions that do not consume characters in the target sequence: they do not describe a character, but a condition that must be fulfilled before or after a character.

Characters	Description	Condition for match
^	Beginning of line	Either it is the beginning of the target sequence, or follows a line terminator.
$	End of line	Either it is the end of the target sequence, or precedes a line terminator.
\b	Word boundary	The previous character is a word character and the next is a non-word character (or vice-versa). The beginning and the end of the target sequence are considered here as non-word characters.
\B	Not a word boundary	The previous and next characters are both word characters or both are non-word characters. The beginning and the end of the target sequence are considered here as non-word characters.
(?=subpattern)	Positive lookahead	The characters following the assertion must match subpattern, but no characters are consumed.
(?!subpattern)	Negative lookahead	The characters following the assertion must not match subpattern, but no characters are consumed.

A pattern can include different alternatives

Characters	Description	Effects
\|	Separator	Separates two alternative patterns or subpatterns.