$/ = "";
while(<>) {
    chomp;
    my ($k, $v) = split /\t/;
    my $k1 = (split /\n/, $k, 3)[1];
    my $out = -e $k1 ? "$value\n" : "$key:$value\n";
    open my $ofh, '>>', $k1 or die $!;
    print $ofh $out;
    close $ofh or die $!;
}

foreach my $file (sort glob('./')) {
    open my $ifh, '<', $file or die $!;
    # ... and so on...
}