Regular expression (also known as regex or regexp) provides a way of specifying a pattern to be matched in a given big chunk of text data. It supports a set of characters to specify the pattern. It is widely used for a text search and string manipulation. A lot of shell commands provide an option to specify regex such as grep, sed, find, and so on.

The regular expression concept is also used in other programming languages such as C++, Python, Java, Perl, and so on. Libraries are available in different languages to support regular expression's features.