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Regular Expressions Cheatsheet (PCRE)



Regular Expression Basics


Any character except newline


The character a


The string ab


a or b


0 or more a's


Escapes a special character



Regular Expression Quantifiers


0 or more


1 or more


0 or 1


Exactly 2

{2, 5}

Between 2 and 5


2 or more

Default is greedy. Append ? for reluctant.


Regular Expression Groups


Capturing group


Capturing group named Y


Non-capturing group


Atomic group


Duplicate group numbers


Match the Y'th captured group


Match the named group Y


Recurse into entire pattern


Recurse into numbered group Y


Recurse into named group Y


Match the named or numbered group Y


Recurse into named or numbered group Y




Regular Expression Character Classes


One character of: a, b, c, d


One character except: a, b, c, d


Backspace character


One digit


One non-digit


One whitespace


One non-whitespace


One word character


One non-word character



Regular Expression Assertions


Start of string


Start of string, ignores m flag


End of string


End of string, ignores m flag


Word boundary


Non-word boundary


Start of match


Positive lookahead


Negative lookahead


Positive look-behind


Negative look-behind





Regular Expression Escapes


Remove special meaning


Regular Expression Flags


Ignore case


^ and $ match start and end of line


. matches newline as well


Allow spaces and comments


Duplicate group names allowed


Ungreedy quantifiers


Set flags within regex



Regular Expression Special Characters




Carriage return




Null character


Octal character YYY


Hexadecimal character YY


Hexadecimal character YY


Control character Y



Regular Expression Posix Classes


Letters and digits




ASCII codes 0 - 127


Space or tab only


Control characters


Decimal digits


Visible characters, except space


Lowercase letters


Visible characters


Visible punctuation characters




Uppercase letters


Word characters


Hexadecimal digits



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Last modified: Tuesday, January 24, 2017

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