Q: What is the regular expression ?
A: The regular expression (written as regexp below) is a grammar, to pick up some "you-like" string from a long string, according to your given rule.
Q: Why I should learn regexp?
A: Some advantages here:
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Universal: People around the world are using it.
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Simple: Simple grammar, easy to learn.
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Powerful: Do almost everything you want.
Q: How to learn regexp?
A: Here is the right place to start! The following is a catalog!