use strict;
use warnings;
use feature qw{ say };

sub load {
    my ($file, $table, $phase) = @_;
    open my $in, '<', $file or die "$file: $!";
    while (<$in>) {
        chomp;
        my @columns = split /\t/;
        my $id = join '_', @columns[0, 1];
        die "Duplicate $id."
            if 'first' eq $phase && exists $table->{$id};

        push @{ $table->{$id} }, $columns[2];
        say join "\t", @columns[0, 1], @{ $table->{$id} }
            if 'print' eq $phase;
    }
}

my %table;
my $phase = 'first';
while (my $file = shift @ARGV) {
    load($file, \%table, $phase);
    $phase = 1 == @ARGV ? 'print' : '';
}