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Regular Expressions Overview

Regular Expressions Overview

^ Start of string, or start of line if multiline
$ End of string, or end of line if multiline
\A Start of string
\Z End of string
\b Word boundary
\B Not word boundary
\G The match must occur at the point where the previous match ended

?= Lookahead
?! Negative lookahead
?<= Lookbehind
?!= Negative lookbehind
?() Conditional (if then)
?()| Conditional(if then else)
?# Comment

Character Classes
[chars] Any single character in chars
[^chars] Any single character not in chars
[first-last] Character range: Matches any single character in the range from first to last
. Wildcard: Matches any single character except \n
\d Any digit
\D Any non-digit
\w Any word character
\W Any non-word character
\s Any whitespace character
\S Any non-whitespace character
\p{name} Any character from a Unicode category or named block
\P{name} Any character not from a Unicode category or named block

Character Escapes
\a Alarm (beep)
\b In a character class, matches a backspace character
\e Escape
\n Newline
\r Carriage Return
\f Form feed
\t Horizontal Tab
\v Vertical tab, x0B
\Ooctal Character specified by a two-digit octal code
\xhex Character specified by a two-digit hexadecimal code
\uhex Character specified by a four-digit hexadecimal code
\cchar Named control character

. Any character (except newline)
(a|b) Alternation, a or b
(...) Group
(?:...) Non-capturing group
\n nth group/subpattern
\k<name> named group 'name'

g Global match
i Case-insensitive
m Multiline
s Single line
x Allow comments and white space in pattern
e Evaluate replacement
U Ungreedy pattern

POSIX Character Classes
[:alnum:] Digits and letters
[:alpha:] All letters
[:ascii:] ASCII characters
[:blank:] Space and tab
[:cntrl:] Control characters
[:digit:] Digits
[:graph:] Printed characters
[:lower:] Lower case letters
[:print:] Printed characters and spaces
[:punct:] Punctuation
[:space:] Blank characters
[:upper:] Upper case letters
[:word:] Digits, letters and underscore
[:xdigit:] Hexadecimal digits

* 0 or more
+ 1 or more
? 0 or 1 time
{n} Exactly n times
{n,} At least n times
{n,m} At least n times, but no more than m times

Note: Add ? to a quantifier to make it lazy


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