As someone who works in security, you often have to deal with large quantities of information (in the form of log files, internet packets, etc.). You also likely have to design firewall rules, analyze internet traffic, or set up malware scanners.

Regex is the most underrated security skill that can help you accomplish these tasks. This article is going to break down the most useful RegEx tips and show you how to use them to automate complex tasks.

Regex Syntax Overview

A regular expression, or “RegEx”, is a special string that describes a search pattern.

You can think of RegEx as consisting of two different parts: constants and operators. Constants are sets of strings, while operators are symbols that denote operations over these strings. These two elements together make RegEx a powerful tool of pattern matching.

For example, the regular expression below matches every IP address from subnet 192.168.0.0/24. The highlighted portions are constants, meaning that the RegEx will match the highlighted strings literally. The rest of the RegEx are operators: they have special meanings and add flexibility to the pattern matching.

Shell

192\.168\.0\.\d{1,3}

Different Regex Flavors

Before we dive into the basics of RegEx syntax, please note that RegEx has many different versions. Different software and RegEx engines will often have their own specificities, and it’s best to check the official documentation pages for a full reference of the RegEx version that you are using. However, all RegEx tends to build upon the same set of generic rules.

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