sub check_file {
   my $filename = shift;
   my $string = shift;

   open(F, "< $filename") or die "$filename: $!";
   while(<F>) {
      close(F), return 1 if /\Q$string\E/;
   }
   close(F);
   return
}

if (search_file('file1', 'string1') &&
    search_file('file2', 'string2'))
{
   print "OK\n";
} else {
   print "No\n";
}