exec.rb

#!/usr/bin/env ruby
require 'libssh'

GC.stress = true
puts "libssh #{LibSSH::LIBSSH_VERSION}"
puts LibSSH.version
session = LibSSH::Session.new
# session.log_verbosity = :debug
session.host = 'barkhorn'
session.parse_config
session.add_identity('%d/id_ed25519')

session.connect
if session.server_known == LibSSH::SERVER_NOT_KNOWN
  pubkey = session.get_publickey
  print "Connect to #{pubkey.type_str} #{pubkey.sha1_hex} ? (y/N) "
  $stdout.flush
  yesno = $stdin.gets.chomp
  if yesno != 'y'
    raise
  end
  session.write_knownhost
  puts 'Wrote known_hosts'
elsif session.server_known != LibSSH::SERVER_KNOWN_OK
  raise
end

session.userauth_none
list = session.userauth_list
unless list.include?(:publickey)
  raise "publickey is unsupported: #{list}"
end

if session.userauth_publickey_auto != LibSSH::AUTH_SUCCESS
  raise 'authorization failed'
end

bufsiz = 16384

channel = LibSSH::Channel.new(session)
channel.open_session do
  channel.request_exec('ps auxf')
  until channel.eof?
    LibSSH::Channel.select([channel], [], [], nil)
    out = channel.read_nonblocking(bufsiz)
    if out && !out.empty?
      $stdout.write(out)
    end
    err = channel.read_nonblocking(bufsiz, stderr: true)
    if err && !err.empty?
      $stderr.write(err)
    end
  end
end