Regular Expressions

A cheat sheet with regular expressions.

Special characters and their meanings

Character	Meaning	Example
*	Match zero, one or more of the previous	Ca* matches C or Ca or Caaaa
?	Match zero or one of the previous	Ca? matches C or Ca, but not Caaa
+	Match one or more of the previous	Ca* matches Ca or Caaaa, but not C
\	Used to escape a special characters \ ? ( ) [ ] |	C:\\ matches C:\
.	Wildcard character, matches any character	Ca.* matches Canada, Can't, Caught, etc.
( )	Group characters	See example for |. Can also be used for replacing text with \1, \2, etc.
[ ]	Matches a range of characters	[cbf]ar matches car, bar, far. [0-9]+ matches any integer. [a-zA-Z] matches ASCII letters a-z (upper and lower case) [^0-9] matches any character not 0-9
|	Matches previous OR next character/group	(Mon|Tues)day matches "Monday" or "Tuesday"
{ }	Matches a specified number of occurrences of the previous	[a-z]{3} matches any 3 character string using characters a-z. Eg. abc, xyz. [0-9]{2,4} matches any 2 to 4 digit number. Eg. 23, 349, 5934. [a-z0-9]{2,} matches any alpha-numeric lowercase string longer than 2 characters. Eg. a9, c1cd...
^	Beginning of a string or negation in a range.	^http:\/\/ matches anything starting with http:// [^0-9] matches any character not 0-9.
$	End of a string.	\.exe$ matches anything ending with .exe

POSIX character classes

Character Class	Meaning
[:alpha:]	Any letter, [A-Za-z]
[:upper:]	Any uppercase letter, [A-Z]
[:lower:]	Any lowercase letter, [a-z]
[:digit:]	Any digit, [0-9]
[:alnum:]	Any alphanumeric character, [A-Za-z0-9]
[:xdigit:]	Any hexadecimal digit, [0-9A-Fa-f]
[:space:]	A tab, new line, vertical tab, form feed, carriage return, or space
[:blank:]	A space or a tab.
[:print:]	Any printable character
[:punct:]	Any punctuation character: ! ' # S % & ' ( ) * + , - . / : ; < = > ? @ [ / ] ^ _ { | } ~
[:graph:]	Any character defined as a printable character except those defined as part of the space character class
[:word:]	Continuous string of alphanumeric characters and underscores.
[:ascii:]	ASCII characters, in the range: 0-127
[:cntrl:]	Any character not part of the character classes: [:upper:], [:lower:], [:alpha:], [:digit:], [:punct:], [:graph:], [:print:], [:xdigit:]

Other notes

Usage with sed

When using sed, you need to escape special characters like (), {}, and /. For example:

$ cat file | sed 's/\(9[0-9]\{1\}%\)/<strong style="color:orange">\1<\/strong>/'