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Published 08/06/2002

Appendix A

Regular Expressions

This chapter provides a brief introduction to regular expressions.

Regular Expressions

The REGEX operator uses regular expressions to evaluate the contents of a field. Regular expressions test whether the contents match a pattern that you specify. If a field's contents match a regular expression, the rule returns true.

Regular expressions contain the following types of information:

• Characters that match themselves. For example, the regular expression testing will match a field that contains the text testing.
• Metacharacters that modify the meaning of other characters.

Metacharacters

Table 11 shows some metacharacters that are often used in regular expressions.

Table 11 Regular Expression Metacharacters 

Character	Description	Example
.	Matches any single character.	b.g matches bug, bag, and bog. It does not match bg or boogie.
*	Matches zero or more occurrences of the preceding character (which can also be a metacharacter).	bugs* matches bugs, bugss, and bugsy. It does not match bugout.
^	Matches the beginning of the string.	^tooth matches toothpaste and toothbrush. It does not match falsetooth.
$	Matches the end of the string.	bag$ matches totebag and sportbag. It does not match baggie.
\	Indicates that the following character should not be treated as a metacharacter.	test\* matches test*. It does not match testt or testtt.
[ ]	A set of characters, only one of which is needed for a match.	bu[gt] matches bug and but. It does not match bun, buzz, or butter. number[0-9] matches number3 and number7. It does not match numbers.
+	Matches one or more occurrences of the preceding character (which can also be a metacharacter).	ba+g matches bag and baaggie. It does not match bg or baieg.
?	Matches zero or more occurrences of the preceding character (which can also be a metacharacter).	ba?g matches bag and bg. It does not match baaggie or baeig.