use strict;
use warnings;

my $spat = qr/(?:abc|xyz)/;

while(<DATA>) {
        chomp;
        my $r = $_;
        my @flds = unpack "(A3)*", $r;

        print "$r => ";
        do { print "$_ " if /$spat/ } for @flds;
        print "\n";
}
__DATA__
abcmmmnnn
mmmxyznnn
xyzfooabc
mabcmxyzm