use strict;
use warnings;

my $folder_IN     = $ARGV[0];
my $finaltreefile = "./final.CSV";
my $level = 0;
my $rootfile      = `ls $folder_IN/$level*.CSV`;
chomp($rootfile);
print "rootfile: $rootfile\n";


open( my $final, '>', $finaltreefile ) or die "$finaltreefile: $!";

treebuilder($rootfile, $level+1);

close($final);

exit(0);



sub treebuilder {
    my $filename = shift;
    my $level = shift;
    my $nextlevel = $level + 1;

    print "File level $level : $filename\n";

    my $PRESENTLEVELFILE;
    unless(open($PRESENTLEVELFILE, '<', $filename)) {
        warn "$filename: $!";
        return;
    }


    my $leafline = <$PRESENTLEVELFILE>;
    if ( $filename eq $rootfile ) {
        print $final "0 $leafline";
    }

    while ( my $leafline = <$PRESENTLEVELFILE> ) {
        print "Leggo $leafline\n";
        chomp($leafline);
        print "next level=$nextlevel\n";
        my @element = split( '§', $leafline );
        print "Find $element[0]\n";
        my $NEXTLEVELFILE =
          $folder_IN . "/" . $level . "_" . $element[0] . ".CSV";
        print "Check if file exists: $NEXTLEVELFILE\n";
        print $final "$level $leafline\n";
        treebuilder($NEXTLEVELFILE, $nextlevel);
    }
    close($PRESENTLEVELFILE);
}

##</code><code>##

0 440Z0220-932§other information
1 623Z5400-1§other information
1 623Z5400-1§other information
1 623Z5400-18other information
1 623Z5400-18§other information
1 623Z5400-3§other information
1 623Z5420-1301§other information
1 623Z5420-1307§other information
1 7010902H01§other information
1 7010900H01§other information
1 623Z5466-1013§other information
1 623Z5466-1015§other information
1 623Z5465-1039§other information
1 623Z5465-1041§other information
1 623Z5465-1001§other information
2 623Z5465-1§other information
2 623Z5465-11§other information
2 CA623Z5465-1001§other information
1 623Z5420-3301§other information
1 623Z5465-41§other information
1 623Z5462-1001§other information
1 623Z5462-1003§other information
2 623Z5468-1§Other information
2 623Z5468-9§Other information
2 623Z5468-7§Other information
2 623Z5468-5§Other information
2 CA623Z5462-1003§Other information
2 BACD40AC36B30§Other information
2 623Z5469-7§Other information
2 623Z5462-3§Other information
1 7010902H01§other information
1 623Z5420-3307§other information
1 B3-15838§other information
1 623Z5422-3307§other information

##</code><code>##

sub treebuilder {
    my ($filename, $level) = @_;

    my $PRESENTLEVELFILE;
    unless(open($PRESENTLEVELFILE, '<', $filename)) {
        warn "$filename: $!";
        return;
    }

    my $leafline = <$PRESENTLEVELFILE>;
    print $final "0 $leafline" if ( $filename eq $rootfile );

    while ( my $leafline = <$PRESENTLEVELFILE> ) {
        print $final "$level $leafline";
        my @element = split( '§', $leafline );
        treebuilder("$folder_IN/${level}_$element[0].CSV",$level + 1);
    }
    close($PRESENTLEVELFILE);
}