bikeNomad already answered your question, just let me elaborate a little bit on some of your statements

• (Honestly, I don't know why; this was a suggestion from a more experienced engineer, ...)

  you should always try to see the logic behind such statements. In your case of matching different pattern against a string, this solution might be more effective (to shorten my code, consider $string to be in $_): if (/($m1)/ || /($m2)/ || /($m3)/) This is quicker then your big regex if you know that $m1 will be more frequent than $m2 (which in turn is more frequent than $m3).
  The explanation is simple, in your case the regex engine has to check all three patterns for every position in the string. With the || construct, the checking of the $m2 and $m3 pattern might not be necessary. So you see, it pays off, to know your data. (Remark: In general, the size of a regex says nothing about its execution time, only the compile time increases. Execution time depends on the content!)
• If speed is an issue, consider the /o modifier and qr//. Furthermore you might try to lowercase the whole string and the patterns instead of matching /i. And studying the string might also help.
• For all this advice, the 'correct' way can be found out by using Benchmark on some real data. By doing that you can find out yourself what works when and don't have to rely on some 'experts'.

• The FAQs/resources don't offer any aid, and other Perl wizards say it can't be done.

  Just to show you TMTOWTDI - not that I recommend this if (/($m1(?{$match=1})|$m2(?{$match=2})|$m3(?{$match=3}))/) { ... you can execute code from within the regex ... and this is a really bad example of this powerful feature - but a way to do it :)

-- Hofmator

If you happen to have a lot of patterns to match, I like the "build a sub on the fly" approach

     my @patterns = qw/ foo bar baz /;

     ## if you need to return the pattern itself, return '$_' instead
     my $match_n_return = join( "\n",
              map{  "return \$1 if \$_[0] =~ /$_/o;" } @patterns
     );
     my $sub =  eval qq|sub  { $match_n_return return undef }|;
     if( $@ ) {
           ## some syntax error in the eval string
           die $@
      }

      my $matched = $sub->( "string you want to match" );
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The only problem here is, you don't get a fine granularity of control for each match. But I like the fact that this can be used over and over, and that since all the regexes are pre-compiled, you save some time for repeated use

Let's just say that you end up with three different regexs. You deside to write three different ones because it would have made the single combined regex a god-awful mess. Good. Now, if you use Hofmator's suggestion, you'll get something like this:

if ($string =~ /re1/ || $string =~ /re2/ || $string =~ /re3/)
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if      ( $string =~ /re1/ ) {
#do thing 1
} elsif ( $string =~ /re2/ ) {
#do thing 2
} elsif ( $string =~ /re3/ ) {
#do thing 3
}
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Scott

Remember to use quotemeta or \Q and \E on any variables you are going to use inside a regex. If you forget to, and any special regex meta-characters exist in your variables, your program can do anything between match unwanted strings to completely die'ing.

I see this problem in alot of code where the program "builds" a regex. Bugs caused by forgetting to do this can go undetected for a long time until a "+", "|" or a ")" occurs somewhere in the incoming data. (assuming the data being searched through is not hard coded into the script, and thus it's content controlled by the programmer - as it's often not in the real world)

Here's some sample code to illustrate the use of quotemeta in solving your problem:

#!/usr/bin/perl -w

use strict;

use constant STRING   => 'clintonesque';
use constant TO_MATCH => qw(
  Clinton
  Bush
  Reagan
);

my $regex = join '|', map { quotemeta } TO_MATCH;

my ($first_match) = STRING =~ /($regex)/i;

print $first_match;
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