Regular Expressions for Filters¶
A regular expression is a text model formed of ordinary characters (for example, letters from a to z) and special characters known as metacharacters. The model describes one or several strings that coincide when searching a text body. The regular expression is used as a template to collate a model of characters with the string being searched.
The table below includes a complete list of metacharacters and their behavior in the context of the regular expressions:
|X||The character x|
|\||The character \|
|[abc]||a, b, or c|
|[^abc]||Any character except a, b, or c (negation)|
|[A-Z]||From A to Z inclusive|
|X?||X, once or never|
|X*||X, zero or more times|
|X+||X, once or more times|
|XY||X followed by Y|
|X|Y||X or Y|
|(X)||X, as a group|
Groups are enumerated by counting the brackets open from left to right. The zero group refers to the complete expression.
\ character can be used to escape the metacharacters used in
the expressions. For instance, the
\\ expression represents a
\( represents a parenthesis.