Mastering Linux Shell Scripting - Second Edition

Regular expression engines

To start with, what are regular expressions?

Regular expressions are strings that the regex engine interprets to match a specific text. It's like an advanced way of searching.

Assume that you want to search a file for lines starting with any small letters, or you want to search for lines that contain a number, or maybe search for lines starting with specific text. The normal search can't be generic: the only way to do that is to use regular expressions.

And what is the regex engine?

The regex engine is the piece of software that understands these strings and translates them to find the matched text.

There are many regex engines out there; for example, the engines that are shipped with programming languages such ...