Regular expressions (which will now be referred to as "regexes") are basically pattern matching inside of text. They use special syntax and concepts in order to obtain information from a string. Many programming languages have some sort of support for regexes, because of the sheer usefulness of them. Not only can patterns be used to validate that a certain pattern exists in a string, but they can also be used to physically extract matched portions and make them usable in your PHP code.

They look at some of the basics - example structure, metacharacters, greediness as well as include a brief comparison of PCRE versus POSIX versions. The tutorial is peppered with plenty of example expressions too, giving you a good idea of what you're working towards knowing.

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