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:
Expression |
Matches |
---|---|
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 |
. |
Any character |
^ |
Line start |
$ |
Line end |
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.
The \
character can be used to escape the metacharacters used in
the expressions. For instance, the \\
expression represents a
single \,
and \(
represents a parenthesis.