Re: Dynamic regexp from array values

[jdporter]

Regexes are just strings (well, at least you can think of them that way), which means you can build them up just as you would any other strings.

  my $regex = join '|', @all_the_different_values;

  if ( $data =~ /$regex/ ) . . .

If you need only exact matches, then you should probably write it as

  if ( $data =~ /^($regex)$/ ) . . .

On the other hand, unless you're using the power of regexes to do something like "wildcard" matching, there's another way to do it you should consider: Make a "set" of the values, and test for the existence of $data in that set.

  my %set;
  @set{ @all_the_different_values } = (); # make the set

  if ( exists $set{ $data } ) . . .

jdporter
The 6th Rule of Perl Club is -- There is no Rule #6.

[VSarkiss]

jdporter makes a very good point above. I just want to make it explicit because it's a fairly common over-generalization: If you're only testing for string equality, don't use regular expressions at all. I can't tell from your note whether that's the case or not, but if so, a regular expression is much more work than necessary.

In that case, using a hash as shown above will work, and will be faster, though it may consume more memory. Another alternative is to use a simple loop:

foreach (@target_strings)
{
   if ($data eq $_) { doSomething(); last; }
}

(I'm guessing that you can short-circuit the loop if any one of the targets matches.)

[tachyon]

You *must* use quotemeta or \Q \E if you are going to do this and qr// or a /o modifier on the regex is also not a bad idea:

my $re = join '|', map{quotemeta}@vals;
$re = qr/$re/;
if ( $var =~ m/$re/ ) { blah }

If you fail to quotemeta then your regex will either die or commit weirdness if there are any / ( ) { } ^ $ * ? + \ - . chars present in @vals. quotemeta is a vital part of doing this.

cheers

tachyon

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