Regular expressions can be one of the most powerful tools in your toolbox as a Linux user, system administrator, or even as a programmer. It can also be one of the most daunting things to learn, but it doesn't have to be! While there are an infinite number of ways to write an expression, you don't have to learn every single switch and flag. In this short how-to, I'll show you a few simple ways to use regex that will have you running in no time and share some follow-up resources that will make you a regex master if you want to be.
A quick overview
Regular expressions, also referred to as "regex" patterns or even "regular statements," are in simple terms "a sequence of characters that define a search pattern." The idea came about in the 1950s when Stephen Cole Kleene wrote a description of an idea he called a "regular language," of which part came to be known as "Kleene's theorem." At a very high level, it says if the elements of the language can be defined, then an expression can be written to match patterns within that language.
Since then, regular expressions have been part of even the earliest Unix programs, including vi, sed, awk, grep, and others. In fact, the word grep is derived from the command that was used in the earliest "ed" editor, namelyg/re/p, which essentially means[1] "do a global search for this regular expression and print the lines." Cool!
Why we need regular expressions
As mentioned above, regular expressions are used to define a pattern to help us match on or "find" objects that match that pattern. Those objects can be files in a filesystem when using the find command for instance, or