Regular Expressions Reference Sheet


Regular Expressions Reference Sheet

Character Definition Example

^

The pattern has to appear at the beginning of a string. ^cat matches any string that begins with cat

$

The pattern has to appear at the end of a string. cat$ matches any string that ends with cat

.

Matches any character. cat. matches catT and cat2 but not catty

[]

Bracket expression. Matches one of any characters enclosed. gr[ae]y matches gray or grey

[^]

Negates a bracket expression. Matches one of any characters EXCEPT those enclosed. 1[^02] matches 13 but not 10 or 12

[-]

Range. Matches any characters within the range. [1-9] matches any single digit EXCEPT 0

?

Preceeding item must match one or zero times. colou?r matches color or colour but not colouur

+

Preceeding item must match one or more times. be+ matches be or bee but not b

*

Preceeding item must match zero or more times. be* matches b or be or beeeeeeeeee

()

Parentheses. Creates a substring or item that metacharacters can be applied to a(bee)?t matches at or abeet but not abet

{n}

Bound. Specifies exact number of times for the preceeding item to match. [0-9]{3} matches any three digits

{n,}

Bound. Specifies minimum number of times for the preceeding item to match. [0-9]{3,} matches any three or more digits

{n,m}

Bound. Specifies minimum and maximum number of times for the preceeding item to match. [0-9]{3,5} matches any three, four, or five digits

|

Alternation. One of the alternatives has to match. July (first|1st|1) will match July 1st but not July 2

POSIX Character Classes

Character Definition Example

[:alnum:]

alphanumeric character [[:alnum:]]{3} matches any three letters or numbers, like 7Ds

[:alpha:]

alphabetic character, any case [[:alpha:]]{5} matches five alphabetic characters, any case, like aBcDe

[:blank:]

space and tab [[:blank:]]{3,5} matches any three, four, or five spaces and tabs

[:digit:]

digits [[:digit:]]{3,5} matches any three, four, or five digits, like 3, 05, 489

[:lower:]

lowercase alphabetics [[:lower:]] matches a but not A

[:punct:]

punctuation characters [[:punct:]] matches ! or . or , but not a or 3

[:space:]

all whitespace characters, including newline and carriage return [[:space:]] matches any space, tab, newline, or carriage return

[:upper:]

uppercase alphabetics [[:upper:]] matches A but not a

Perl-Style Metacharacters

Character Definition Example

//

Default delimiters for pattern /colou?r/ matches color or colour

i

Append to pattern to specify a case insensitive match /colou?r/i matches COLOR or Colour

\b

A word boundary, the spot between word (\w) and non-word (\W) characters /\bfred\b/i matches Fred but not Alfred or Frederick

\B

A non-word boundary /fred\B/i matches Frederick but not Fred

\A

matches at the beginning of a string  

\Z

matches at the end of a string  

\d

A single digit character /a\db/i matches a2b but not acb

\D

A single non-digit character /a\Db/i matches aCb but not a2b

\G

matches where previous m//g left off (in perl, not so much in PHP)  

\n

The newline character. (ASCII 10) /\n/ matches a newline

\r

The carriage return character. (ASCII 13) /\r/ matches a carriage return

\s

A single whitespace character /a\sb/ matches a b but not ab

\S

A single non-whitespace character /a\Sb/ matches a2b but not a b

\t

The tab character. (ASCII 9) /\t/ matches a tab.

\w

A single word character - alphanumeric and underscore /\w/ matches 1 or _ but not ?

\W

A single non-word character /a\Wb/i matches a!b but not a2b