in reply to read from two files at once?

The problem with:

my ($in) = <CURR>;

Is that it puts <CURR> in list context. That causes it read all the lines in your file and then put the first one in $in! Instead you want:

my $in = <CURR>;

Which will read just one line. Reading from two files should work with something like:

open FILE1, "<", "file1.txt" or die $!; open FILE2, "<", "file1.txt" or die $!; while (!eof(FILE1) and !eof(FILE2)) { my $line1 = <FILE1>; my $line2 = <FILE2>; # ... }