Regular Expressions Reference Sheet
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Yeah, kitt finished writing this at 22:13 on 2 September 2004
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 |