The Anonymonk is close, but I prefer a solution that works without code assertions:

#!/usr/local/bin/perl -w
use strict;
my @pattern = ('B.B', 'CB');

my $re = qr/^(.*?)(?:@{[ join "|", map "($_)", @pattern ]})/;

foreach (qw(ABCBXBCA APCBXBCAC)){
        if(my ($keyword,@match) = /$re/) {
                my $i = 0; 
                $i++ until defined shift @match; 
                print "String:$_ Pattern:$pattern[$i] KeyWord:$keyword
+\n";
        }       
}
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The key is that I capture separately for each pattern.

Update: per jryan's point, edited to generate the regex once before the loop.

Makeshifts last the longest.