I'm sorry to say it, but File::DirWalk is not a very well written module. To do what you want to do properly, you have to reach into the object, breaking its encapsulation. (Hey, at least it's possible. :-) And the module's documentation is poor, in that it does not tell you what the depth parameter is really for or how it's used.

The following works:

for my $directory ( @directory )
{
    my $dw = new File::DirWalk;
    $dw->onDirLeave(
        sub{
            my $dir = shift;
            if ( $dw->{'depth_count'} == $depth )
            {
                push @folder, $dir;
            }
            return File::DirWalk::SUCCESS;
        }
    );
    $dw->setDepth( $depth + 1 );
    $dw->walk( $directory );
}
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Note two things:

1. The test of the object's data member 'depth_count' against $depth;
2. passing $depth + 1 to the setDepth method.

Just for fun, here's how I'd probably write the above:

my $dw = new File::DirWalk;

    sub on_dir_leave
    {
        $dw->{'depth_count'} == $depth and
            push @folder, shift;
        File::DirWalk::SUCCESS
    }

$dw->onDirLeave( \&on_dir_leave );
$dw->setDepth( $depth + 1 );

$dw->walk( $_ ) for @directory;
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