I think the problem is that what you have still reads everything into @subfolders. Here's the snippet I'm talking about.

open(FFINFO,"$folderfolder_file") or die "Can't open $folderfolder_fil
+e: $!\n";
# This reads in every line from FFINFO
my @subfolders = <FFINFO>;

my %parents_of;
my $parentid;

# This loop also wants to read every line,
# but the handle is already at EOF,
# so it gets nothing.
while ( my $line = <FFINFO> ) {
[download]

If you need @subfolders for some purpose outside the code we're talking about, you could still have it. Just declare my @subfolders; at the same scope as $parentid and %parents_of, without initializing it. Then, right inside the FFINFO read loop, push every $line in. It winds up looking like this:

open(FFINFO,"$folderfolder_file") or die "Can't open $folderfolder_fil
+e: $!\n";

my @subfolders;
my %parents_of;
my $parentid;

while ( my $line = <FFINFO> ) {
    push @subfolders, $line;
[download]

You also had a question about this:

    return @parents ? [ map {
                                map { "$_/$folderid" } @{ build_path( 
+$_ ) }
                            } @parents ]
                    : [ $folderid ];
[download]

What this means is, "if @parents is non-empty, return first expression (with nested maps), else return the second expression ($folderid alone in an array reference)." Your description leads me to believe that you have the precedence mixed up. What you describe is this:

( return @parents ) ? [ X ] : [ Y ];
[download]

What's happening is this:

return ( @parents ? [ X ] : [ Y ] );
[download]

You can see this kind of thing yourself using B::Deparse. I ran this command line:

perl -MO=Deparse,-p input-file.pl
[download]

With the -p, it puts parentheses in to clarify how expressions are interpreted. As a result, it showed me this (along with all the other code):

return((@parents ? [map({map({"$_/$folderid";} @{build_path($_);});} @
+parents)] : [$folderid]));
[download]

That's not pretty, but it does show that the return is "outside" the whole rest of the line.

I hope this helps. I feel I've written in some haste, so I wouldn't be surprised if I've been unclear. If I have left you with any other questions, feel free to ask.

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