>>601
早速ありがとうございます。
そのままの記述でテストしたところ

Warning: fopen(test.dat) [function.fopen]: failed to open stream: Permission denied in /var/www/vhosts/localhost/httpdocs/test.php on line 3

Warning: fwrite(): supplied argument is not a valid stream resource in /var/www/vhosts/localhost/httpdocs/test.php on line 4

Warning: fclose(): supplied argument is not a valid stream resource in /var/www/vhosts/localhost/httpdocs/test.php on line 5

とのエラー文が出てしまいます。