GNU grep is an amazing power tool for finding words, numbers, spaces, punctuation, and random text strings inside of files, and this introduction will get you up and running quickly.
We’ll stick to GNU grep and the Bash shell, because both are the defaults on most Linux distros. You can verify that you have GNU grep, and not some other grep:
$grep -Vgrep (GNU grep) 2.21Copyright (C) 2014 Free Software Foundation, Inc.
It’s unlikely that you will bump into a non-GNU grep on Linux unless you put it there. There are some differences between GNU grep and Unix grep, and these are often discussed in documentation and forums as though we spend our days traipsing through multiples Linuxes and Unixes with gay abandon. Which sounds like fun, but if you use only Linux then you don’t need to worry about any …