open(KEYWORDS,"/tmp/file1") 
  or die "cannot open /tmp/file1: $!";
my %keywords=  map { ($_, 1) } <KEYWORDS>; # create a hash keyword => 1
open(STUFF_TO_MATCH,"/tmp/file2");
  or die "cannot open /tmp/file2: $!";
while(<STUFF_TO_MATCH>)
  { print "$_ matched!\n" if($keyword{$_}); }