my %reversetbl;  # at the beginning

# ... open each file ...
while (<$fh>) {
	chomp; # remove newline
	# ...
	$reversetbl{$_}{$curdir}++;
}

# at the end:
for my $k (keys %reversetbl) {
	print $k, ';', join(',', keys %{ $reversetbl{$k} } ), "\n";
}