Regular Expression Syntax in PHP

Regular Expression Syntax

^ – Start of string

$ – End of string

. – Any single character

( ) – Group of expressions

[] – Item range ( e.g. [afg] means a, f, or g )

[^] – Items not in range ( e.g. [^cde] means not c, d, or e )

- (dash) – character range within an item range ( e.g. [a-z] means a through z )

| (pipe) – Logical or ( e.g. (a|b) means a or b )

? – Zero or one of preceding character/item range

* – Zero or more of preceding character/item range

+ – One or more of preceding character/item range

{integer} – Exactly integer of preceding character/item range ( e.g. a{2} )

{integer,} – Integer or more of preceding character/item range ( e.g. a{2,} )

{integer,integer} – From integer to integer (e.g. a{2,4} means 2 to four of a )

\ – Escape character

[:punct:] – Any punctuation

[:space:] – Any space character

[:blank:] – Any space or tab

[:digit:] – Any digit: 0 through 9

[:alpha:] – All letters: a-z and A-Z

[:alnum:] – All digits and letters: 0-9, a-z, and A-Z

[:xdigit:] – Hexadecimal digit

[:print:] – Any printable character

[:upper:] – All uppercase letters: A-Z

[:lower:] – All lowercase letters: a-z