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wtd

Sat Nov 13, 2004 9:46 pm


[Regex-tut] Multiples

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It's either there or not

In the last tutorial I spoke of alternatives, groups and sets.  The last regex used was:

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

Now, what if I want to either recognize that comma or not?  This is a multiples situation.  I want either one comma or none.  The ? suffix provides this.

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

Once, and maybe more... oh, and something else

Now, you'll also notice that I put one space between the greeting/parting and world.  What difference does it make to me if someone uses one or more spaces?  Maybe they used a tab.  It's all the same to me.

The \s entity respresents any whitespace, so a simple rewrite looks like:

/([hH]ello|[tT]oodles),?\sworld/

Now, I still have the problem of wanting to match the string even if someone has used more than one space.  The + suffix handles this nicely.

/([hH]ello|[tT]oodles),?\s+world/

Maybe nobody's home, or maybe there's a party going on

I mentioned in a previous tutorial that ^ and $ are sued to represent the beginning and end of the string.  So let's say I want to include those:

/^([hH]ello|[tT]oodles),?\s+world$/

Of course, now I can't have anything before the greeting/parting or after world.  But that's what I wat, right?

Yes.  On the other hand, what do I care if the stuff before or after the expression I'm looking for is just empty space?  

I want to look for any number of spaces, and I also want to be able to match no spaces.  The * suffix will handle this for me.

/^\s*([hH]ello|[tT]oodles),?\s+world\s*$/