コマンド
$ nc -z host.example.com 20-30
結果
Connection to host.example.com 21 port [tcp/ftp] succeeded! Connection to host.example.com 22 port [tcp/ssh] succeeded! Connection to host.example.com 25 port [tcp/smtp] succeeded!
$ nc -z host.example.com 20-30
Connection to host.example.com 21 port [tcp/ftp] succeeded! Connection to host.example.com 22 port [tcp/ssh] succeeded! Connection to host.example.com 25 port [tcp/smtp] succeeded!