Regular Expressions: An Introduction
Published: January 12, 2004
User Rating: 8.9 (257 votes)
What is a regular expression ?
"A regular expression is a pattern that is matched against a subject string from left to right". Well, that was textbook answer. But in simple terms, regular expression is a string used for find and replacing strings in other large strings.
You can even say that regular expression (a.k.a regex or regexp) are fourth generation (4G) wilcards, that we used in the good ol' days of DOS.
(But don't say that I said so, otherwise those perl experts are going to bite my head off for this remark. Why ? Because ... regexp are so powerful, yet easy to use, and saying that they are just wilcard, would be an insult. So i didn't say it, ok)
Why use regular expression ?
In the good old dos prompt, typing
would actually display all the files. Meaning the pattern * means "match anything".
So if you were to write this is in the regular expression, you would write