Nginx HTTP Server - Fourth Edition

Purpose

The first question we must answer is: what is the purpose of regular expressions? To put it simply, the main purpose is to verify that a string of characters matches a given pattern. The pattern is written in a particular language that allows for defining extremely complex and accurate rules:

String	Pattern	Does it match?	Explanation
hello	^hello$	Yes	The string begins with character h (^h), followed by e, l, l, and then finishes with o (o$).
hell	^hello$	No	The string begins with character h (^h), followed by e, l, l, but does not finish with o.
Hello	^hello$	Depends	If the engine performing the match is case-sensitive, the string doesn't match the pattern.

This concept becomes a lot more ...