A regular expression is a set of pattern matching rules encoded in a string
according to certain syntax rules. Although the syntax
is somewhat complex it is very powerful and allows much more useful pattern matching than say simple wildcards like ? and *.
Example of a Regular expression
Regular expressions originated in the Unix world and are a part of the Perl language. If a regular expression language is similar to Perl's regular expressions, it is called Perl Compliant Regular expression (PCRE for short). This is pretty much a standard.
The .NET framework includes pattern matching classes, as does Java.
Also Known As: PCRE
Regular Expressions can match complicated patterns.