my $match = qr/thunderbird/i;

open FILE, '<', 'foo.txt' or die $!;

while (<FILE>) {
   if ($_ =~ $match) {
      my @word = split /\s+/, $_;
      $_ =~ s/[A-Za-z0-9_ ]//g;
      for my $i (0..$#word) {
         if ($word[$i] =~ $match) {
            print "match found on line $. word ", $i+1,"\n";
         }
      }
   }
}