What is a regular expression?

A regular expression is phrase or formula, representing a pattern. A regular expression allows you to search for strings matching the pattern within a set of documents.

An everyday example of a regular expression is the usage of the wildcard character * when searching for files.

For instance, when using the phrase *.txt during a file search, you have used a simple regular expression to locate text files.
In other words, in this example, the regular expression *.txt represents all files having a name ending in .txt.

In case you want to learn more on regular expressions, please see the right-hand column of this page. There you will find a number of links to very useful regular expression tutorials and regular expression reference sites.

Remember that regular expressions are case sensitive by default!

Online tutorials and reference:

Regular Expressions Tutorial
Regular Expressions Reference
Regular Expressions
Regular Expression Basic Syntax Reference
Regular Expression Examples
Regular Expressions Database

Regular-expression tutorial software:

Regex-coach
Regulator