RegEx

Regular Expressions

Anchors

Syntax	Description
^	Start of string, or start of line in multi-line pattern
$	End of string, or end of line in multi-line pattern

Syntax	Description
*	0 or more
?	0 or 1
+	1 or more
{3}	Exactly 3
{3,}	3 or more
{3,5}	3, 4 or 5
note	Add a ? to a quantifier to make it ungreedy

Syntax	Description
\	Escape following character

Escaping is a way of treating characters which have a special meaning in regular expressions literally, rather than as special characters.

Syntax	Description
.	Any character except new line (\n)
(a\|b)	a or b
(…)	Group, capturing
(?:…)	Passive (non-capturing) group
[abc]	Range (a or b or c)
[^abc]	Not (a or b or c)
[a-q]	Lower case letter from a to q
[A-Q]	Upper case letter from A to Q
[0-7]	Digit from 0 to 7

Use a group to “capture and replace”.

a(bc) parentheses create a capturing group with value bc
The parentheses are used to create “groups,” which then get assigned a base-1 index, accessible in a replace with a $ (i.e., the first parentheses-bounded (characters) become a group that can be referenced by $1, the second group would be $2, the third $3, etc.).
NOTE: in gedit you reference with a backslash: \ not a $ (i.e., \1\2\3, etc.).
See the follow table regarding string replacements.

Note: Some regex implementations use \ instead of $.

Syntax	Description
[:upper:]	Upper case letters
[:lower:]	Lower case letters
[:alpha:]	All letters
[:alnum:]	Digits and letters
[:digit:]	Digits
[:xdigit:]	Hexadecimal digits
[:punct:]	Punctuation
[:blank:]	Space and tab
[:space:]	Blank characters
[:cntrl:]	Control characters
[:graph:]	Printed characters
[:print:]	Printed characters and spaces
[:word:]	Digits, letters and underscore