PHP Regex Cheat Sheet

Special Sequences

• \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 - Case Insensitive
• m - Multiline mode - ^ and $ match start and end of lines
• s - Dotall - . class includes newline
• x - Extended– comments and 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

Assertions

• (?=) - 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 (?
• (?>) - 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)

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