Regular expressions or regex are sequences of characters that define a pattern.
There are three types of regular expressions: regex (OS_Regex), sregex (OS_Match) and PCRE2.
Regex (OS_Regex) syntax
This is a fast and simple library for regular expressions in C.
This library is designed to be simple while still supporting the most common regular expressions.
Sregex (OS_Match) syntax
This is faster than OS_Regex, but only supports simple string matching and the
following special characters.
Perl Compatible Regular Expressions (PCRE) tries to match Perl syntax and semantics as closely as it can.
It provides features like recursive patterns, look-ahead and look-behind assertions, non-capturing groups, non-greedy quantifiers, extended syntax for characters and character classes, and many other. For more details, please refer to the PCRE Syntax documentation.