rubysshnet-ssh

How to get exit status with Ruby's Net::SSH library?


I have a snippet of code, simply trying to execute a script on a remote server, in the event that it fails, I'd like to make a follow-up call, imagine this:

require 'rubygems'
require 'net/ssh'
require 'etc'

server = 'localhost'

Net::SSH.start(server, Etc.getlogin) do |ssh|
  puts (ssh.exec("true")  ? 'Exit Success' : "Exit Failure")
  puts (ssh.exec("false") ? 'Exit Success' : "Exit Failure")  
end

I would expect (ignoring that stdout and stderr are printed in my contrived example) - but first line should exit with 0 which I would expect Ruby would interperate as false and display "Exit Failure" (sure, so the logic is wrong, the ternary needs to be flipped) - but the second line should exit with the opposite status, and it doesn't.

I can't even find anything in the documentation about how to do this, and I'm a little worried that I might be doing it wrong?!


Solution

  • I find the following way of running processes with Net::SSH much more useful. It provides you with distinct stdout and stderr, exit code and exit signal.

    require 'rubygems'
    require 'net/ssh'
    require 'etc'
    
    server = 'localhost'
    
    def ssh_exec!(ssh, command)
      stdout_data = ""
      stderr_data = ""
      exit_code = nil
      exit_signal = nil
      ssh.open_channel do |channel|
        channel.exec(command) do |ch, success|
          unless success
            abort "FAILED: couldn't execute command (ssh.channel.exec)"
          end
          channel.on_data do |ch,data|
            stdout_data+=data
          end
    
          channel.on_extended_data do |ch,type,data|
            stderr_data+=data
          end
    
          channel.on_request("exit-status") do |ch,data|
            exit_code = data.read_long
          end
    
          channel.on_request("exit-signal") do |ch, data|
            exit_signal = data.read_long
          end
        end
      end
      ssh.loop
      [stdout_data, stderr_data, exit_code, exit_signal]
    end
    
    Net::SSH.start(server, Etc.getlogin) do |ssh|
      puts ssh_exec!(ssh, "true").inspect
      # => ["", "", 0, nil]
    
      puts ssh_exec!(ssh, "false").inspect  
      # => ["", "", 1, nil]
    
    end
    

    Hope this helps.