A regular expression is a special template type allowing you to create effective checks and substring changes in data. An expression consists of usual characters and meta symbols.

Most popular meta symbols and language clauses are:

Item	Match with
^	the beginning of line
$	the end of line
.	any character
[ ]	characters in set
[^ ]	characters not in set
|	previous or next pattern
?	previous pattern 0 or 1 times
+	previous pattern 1 or more times
*	previous pattern 0 or more times
( )	group pattern and remember to \n variable

If part of the expression is enclosed in brackets, after the matching is over, the substring value gets into a variable of the type \n, where n is the number of the expression from the beginning of the string. These variables can be used only in replace actions.

See also: How to...