An Introduction To Regular Expressions

Introduction

As system administrators, developers, QA engineers, support engineers, etc. one needs to find a particular pattern, like a set of IP addresses belonging to certain range or a range of time-stamps or groups of domain or subdomain names, from files. One might also need to find a word spelled in a particular way or find possible typos in a file. This is where regular expressions come in.

Regular expressions are templates to match patterns (or sometimes not to match patterns). They provide a way to describe and parse text. This tutorial will give an insight to regular expressions without going into particularities of any language. We will simply use egrep to explain the concepts.