#!/usr/bin/perl
use warnings;
use strict;

die "type file1 and file2 and output" unless @ARGV==3;
my ($fin1, $fin2, $fout) = @ARGV;

open my $in1, "<", $fin1 or die "Couldn't open '$fin1': $!";
open my $in2, "<", $fin2 or die "Couldn't open '$fin2': $!";
open my $out, ">", $fout or die "Couldn't open '$fout': $!";

<$in1>; <$in2>;  # skip headers

my %ligs;  # lookup table
while (<$in1>) {
    chomp;
    my ($lig, @fields) = split /\t/;
    $ligs{$lig} = [@fields];
}

while (<$in2>) {
    chomp;
    my ($lig, @f2) = split /\t/;
    if (exists $ligs{$lig}) {
        my $f1 = $ligs{$lig};  # get corresponding entry from other file
        my @diffs;
        for (0..$#f2) {
            $diffs[$_] = $f1->[$_] - $f2[$_];
        }
        print $out "$lig\t", join("   ", map sprintf("%.3f",$_), @diffs), "\n";
    }
}

##</code><code>##

...
...
}}}}}}}