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wtd

Sat Nov 13, 2004 9:18 pm


[Regex-tut] Alternatives, Groups, and Sets... oh my!

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Alternatives

Alternatives let us create regular expressions that match one thing or another... or another, or another.

Let's say we want to match a string that contains a greeting for world, regardless of whether the greeting is hello or goodbye.  No exclamation point this time, because I'm not feeling as enthusiastic about this "world" guy.

/Hello, world|Toodles, world/

Groups

Now, we should look at that previous regex:

/Hello, world|Toodles, world/

I've talked about the word "pattern", and you should notice a pattern here.  The only thing that changes is the greeting (or parting) word used.  We can use a group to make the "|" work on only part of the expression.

/(Hello|Toodles), world/

Much better.  This is beginning to look like a pattern.

Sets

Now, why am I being pedantic about use of case?  Shouldn't it be just as friendly if someone used Hello or Toodles without the capital letters?

A set matches any one of the characters contained within it.  So we can use sets comprised of "h", "H", "t" and "T" to do the trick.

/([hH]ello|[tT]oodles), world/