use warnings;
use strict;
use Data::Dumper;

my %collector;

foreach my $file (@ARGV) {
    open my $fh, '<', $file or die $!;
    while (<$fh>) {
        chomp;
        my @vals = split /,/, $_, 4;
        if ( !exists $collector{ $vals[0] } ) {
            $collector{ $vals[0] } = [ @vals[ 1 .. 3 ] ];
        }
        else {
            push @{ $collector{ $vals[0] } }, $vals[2];
        }
    }
}

print Dumper \%collector;