In Linux and Unix, the syntax that is commonly used by many applications for specifying text patterns is known as regular expressions or in short form – regex. Regex is a very powerful technique to describe patterns and many programs use them to describe sequences of characters to be matched. Search programs such as ‘grep’ rely heavily on regex. Basically regex forms the core in the linux world. Many scripting languages such as perl, ruby, php…etc has build in regex functions as well. So you can see, learning regular expression is important because they are used a lot in many places and probably more so in the future.