PHP PCRE Cheat Sheet
Functions
preg_match(pattern, subject[, submatches])
preg_match_all(pattern, subject[, submatches])
preg_replace(pattern, replacement, subject)
preg_replace_callback(pattern, callback, subject)
preg_grep(pattern, array)
preg_split(pattern, subject)
Base Character Classes
\w Any “word” character (a-z 0-9 _)
\W Any non “word” character
\s Whitespace (space, tab CRLF)
\S Any non whitepsace character
\d Digits (0-9)
\D Any non digit character
. (Period) – Any character except newline
Meta Characters
^ Start of subject (or line in multiline mode)
$ End of subject (or line in multiline mode)
[ Start character class definition
] End character class definition
| Alternates, eg (a|b) matches a or b
( Start subpattern
) End subpattern
\ Escape character
Quantifiers
n* Zero or more of n
n+ One or more of n
n? Zero or one occurrences of n
{n} n occurrences exactly
{n,} At least n occurrences
{,m} At most m occurrences
{n,m} Between n and m occurrences (inclusive)
Pattern Modifiers
i Caseless – ignore case
m Multiline mode - ^ and $ match start and
end of lines
s Dotall - . class includes newline
x Extended– comments & whitespace
e preg_replace only – enables evaluation of
replacement as PHP code
S Extra analysis of pattern
U Pattern is ungreedy
u Pattern is treated as UTF-8
Point based assertions
\b Word boundary
\B Not a word boundary
\A Start of subject
\Z End of subject or newline at end
\z End of subject
\G First matching position in subject
Subpattern Modifiers & Assertions
(?:) Non capturing subpattern ((?:foo|fu)bar) matches foobar or fubar without foo or fu
appearing as a captured subpattern
(?=) Positive look ahead assertion foo(?=bar) matches foo when followed by bar
(?!) Negative look ahead assertion foo(?!bar) matches foo when not followed by bar
(?<=) Positive look behind assertion (?<=foo)bar matches bar when preceded by foo
(?<!) Negative look behind assertion (?<!foo)bar matches bar when not preceded by foo
(?>) Once-only subpatterns (?>\d+)bar Performance enhancing when bar not present
(?(x)) Conditional subpatterns (?(3)foo|fu)bar Matches foo if 3rd subpattern has matched, fu if not
(?#) Comment (?# Pattern does x y or z)
