sub recursion
{
    my $plf = shift;
    open my $fh, '<', $plf or die "could not open '$plf' $!";
    
    foreach (my $line = <$fh>){
        if($line =~ /(\w+\.plf)$/)
        {
            $match_plf_name = $1;
            next if $match_plf_name eq $plf;   
            push @recursive_plfs ,$match_plf_name;
            recursion($match_plf_name);
        }
    }
}