The regular expression is a pattern that depicts some text string using literals, operators or constructs.

Regular Expressions are a powerful tool for advanced text work. Most often met when validating data entered by users (such as an email address), but also it can help to find a pattern in the text, or to replace/extract/delete strings.

Before using the regular expression in a program code it’s worth testing it if it works as planned. There are quite a few websites to help you test regular expressions.

Some most popular patterns are in following table.