A regular expression is nothing but a sequence of characters that define a pattern which then can be used to filter or Match information ... Regular expressions are used to identify whether a pattern exists in a given sequence of characters or not and also to locate the position of the pattern in the whole text ... There are multiple regular expression engines like (PCRE, RE2) and programming languages uses or implements One of these engines, as a result, there is a slight difference in syntax and performance across different languages.