use strict;
use vars qw($outfile);
open(DATA, $ARGV[0]) or die "Couldn't open $ARGV[0]: $!";
$outfile = "test.txt";
open (OUT, ">$outfile") || die "Can't open $outfile for creation: $!\n";

my (%hash,@order);
while(<DATA>) {
    chomp;
    my @bits = split /\t/;
    my $first = "$bits[0]"; 
    push @order, $first unless exists $hash{$first};
    $hash{$first} .= ' ' . "$bits[1] $bits[2]\t";
    }
print OUT "$_\t$hash{$_}" for @order;