Regular expressions (regex) provide a concise and flexible means for matching strings of text, such as particular characters, words, or patterns of characters.  A detailed tutorial on regular expressions is beyond the scope of this section.  It provides only a useful mnemonic for regex within VWcms.  Regular expressions can be used in conditional configuration matching, as well as in the VWcms search facility.  Just prefix the expression with a ^ character.

Description		Usage
match-self operator		ordinary characters, e.g. a b c A B C 1 2 3
match-any-character operator		. (period)
concatenation operator		juxtaposition
repetition operators		* + ? {}
alternation operators		|
list operators		[...] [^...]
grouping operators		(...)
back-reference  operator		\digit
anchoring operators		^ $
backslash operator		escape a meta-character, e.g. \ ^ . $ | [ (

The following operators are used to match one, or in conjunction with the repetition operators more, characters of the target string. These single and leading characters are reserved meta-characters and must be escaped using a leading backslash ("\") if required as a literal character in the matching pattern.

Expression		Purpose
^		match the beginning of a line
. (period)		match any character
$		match the end of a line
|		alternation (logical or)
[abc]		match only a, b or c
l[^abc]		match anything except a, b c
[a-z0-9]		match any character in the range a to z or 0 to 9

Repetition operators control the extent, or number, of whatever the matching operators match. These are also reserved meta-characters and must be escaped using a leading backslash if required as a literal character.

Expression		Function
*		match 0 or more times
+		match 1 or more times
?		match 0 or 1 time
{n}		match exactly n times
{n,}		match at least n times
{n,m}		match at least n but not more than m times

Examples

^\.example\.net|example\.net		matches any host name containing the domain example.net
/one/.*|/two/.*		matches paths beginning with /one/ or with /two/
/[0-9]/.*		matches numeric paths (bit contrived)