Mar 172009
 
^ 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, clinic } 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

[: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

// 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
 A word boundary, the spot between word (w) and non-word (W) characters /fred/i matches Fred but not Alfred or Frederick
B A non-word boundary /fredB/i matches Frederick but not Fred
d A single digit character /adb/i matches a2b but not acb
D A single non-digit character /aDb/i matches aCb but not a2b

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

The carriage return character. (ASCII 13) /
/
matches a carriage return
s A single whitespace character /asb/ matches a b but not ab
S A single non-whitespace character /aSb/ matches a2b but not a b
The tab character. (ASCII 9) / / matches a tab.
w A single word character – alphanumeric and underscore /w/ matches 1 or _ but not ?
W A single non-word character /aWb/i matches a!b but not a2b