open (FH,"//192.168.0.11/share/hoge.txt");
opendir (DIR,"192.168.0.11/share");
まあ目的はローカルにあるファイルを共有フォルダへコピーだったので
こんな感じで
use File::Copy;
$dir='//192.168.0.11/share/';
copy $backup_filename,$dir;
open (FH,"//192.168.0.11/share/hoge.txt");
opendir (DIR,"192.168.0.11/share");
use File::Copy;
$dir='//192.168.0.11/share/';
copy $backup_filename,$dir;