my $file1 = "/home/scott/file1"; my $file2 = "/home/scott/file2"; my $hashOfLists; my %hashOfLists; open (FILE1, "$file1") or die "Could not open $file1 $!"; open (FILE2, "$file2") or die "Could not open $file2 $!"; ###################################################### #####This block reads all of the items of the file into #####a hash with the item being the key. Since I ##### was comparing 2 files each key received a #####value of 1 if it was in the first file, 2 if #####it was in both , and 3 if it was only in file 2 ###################################################### foreach () { chomp $_; $hashOfLists{$_} =1; } foreach () { chomp $_; ###################################################### #####if exists checks the hash to see if $_ exists. ##### If true $_'s value becomes 2, #####if false, $_ gets a value of three ###################################################### if (exists $hashOfLists{$_}) { ($hashOfLists{$_}) =2; } else { ($hashOfLists{$_})=3; } } close FILE1 or die "Could not close $file1 $!"; close FILE2 or die "Could not close $file2 $!";