LYCOS RETRIEVER 
Regular Expression: Characters
built 634 days ago
It is an error to use a backslash prior to any alphabetic character that does not denote an escaped construct; these are reserved for future extensions to the regular-expression language. A backslash may be used prior to a non-alphabetic character regardless of whether that character is part of an unescaped construct.
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Some text characters are reserved as regular expression syntax, rather than having its general term. This Wizard recognises this fact, and gives you a check box to decide whether conversion required or not.
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-->Including parentheses in a regular expression pattern causes the corresponding submatch to be remembered. For example, /a(b)c/ matches the characters 'abc' and remembers 'b'. To recall these parenthesized substring matches, use the Array elements [1], ..., [n].
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A regular expression is a pattern that describes what to match during a search. It is often called a regex, regexp or even just RE. The pattern is compiled by a regex engine before it used to match a sequence of characters.
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Being able to match varying sets of characters is the first thing regular expressions can do that isn't already possible with the methods available on strings. However, if that was the only additional capability of regexes, they wouldn't be much of an advance. Another capability is that you can specify that portions of the RE must be repeated a certain number of times.
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Some utitlities and most languages provide extensions or abbreviations to simplify(!) regular expressions. These tend to fall into Character Classes or position extensions and the most common are listed below. In general these extensions are defined by PERL and implemented in what is called PCRE's (Perl Compatible Regular Expressions) which has been implemented in the form of a libary that has been ported to many systems. Full details of PCRE. PERL 5.8.8 regular expression documentation.
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