Regex can be a powerful tool for working with text, but it can also be complex and difficult to master. This cheat sheet provides a quick reference for some of the most common regex patterns and syntax.

POSIX or "Portable Operating System Interface for Unix" is a collection of standards that define some of the functionality that a UNIX operating system should support. One of these standards defines two flavours of regular expressions. Commands involving regular expressions, such as grep and egrep , implement these flavours on POSIX-compliant UNIX systems.