Introduction

A regular expression is a text pattern consisting of a combination of alphanumeric characters and special characters known as meta-characters. A close relative is in fact the wildcard expression, which is often used in file management. The pattern is used to match against text strings. The result of a match is either successful or not, however when a match is successful not all of the pattern must match. This is explained later in the article.

You'll find that regular expressions are used in three different ways: Regular text match, search and replace and splitting. The latter is basically the same as the reverse match i.e. everything the regular expression did not match.

Regular expressions are often simply called regexp's or RE, but for consistency I'll be referring to them with their full name throughout this article.

Due to the versatility of the regular expression, it is widely used in text processing and parsing. UNIX users are probably familiar with them through the use of the programs grep, sed, awk and ed. Text editors such as (X)Emacs and vi also use them heavily. Probably the most known use of regular expressions are in the programming language Perl. You'll find that Perl sports the most advanced regular expression implementation to this day.

In this article I will not concentrate on any particular programming language. Instead, I will provide you with a general overview of regular expressions, from which you can implement into your desired programming/scripting language.

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