Библиотека Net :: SSH включает в себя Net :: SCP , поэтому вам стоит начать поиск там.
Из Сети :: Документы SCP:
require 'net/scp'
# upload a file to a remote server
Net::SCP.upload!("remote.host.com", "username",
"/local/path", "/remote/path",
:password => "password")
# download a file from a remote server
Net::SCP.download!("remote.host.com", "username",
"/remote/path", "/local/path",
:password => password)
# download a file to an in-memory buffer
data = Net::SCP::download!("remote.host.com", "username", "/remote/path")