Net::SSH exec command on remote host

ruby-talk
1

I try to use Net::SSH to exec command on remote host. A session was
openned and a few command should be exec and get the output.
It always failed to get the output of second cmd no matter what
command it is. Here is the code

def do_cmd(s, cmd) #session, command
    s.open_channel do |channel|
    channel.on_data do |ch, data|
      puts "#{data}"
    end
    channel.exec cmd, true
    end
end

  session = Net::SSH.start(h,u,p) #hostname, userid, passwd
  do_cmd(session, "version") # first cmd
  do_cmd(session, "version") # 2nd cmd
  session.loop
  session.close

Here is the error:
/usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/packet-stream.rb:
202:in `<<': can't convert nil into String (TypeError)
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
packet-stream.rb:202:in `read'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
packet-stream.rb:153:in `get'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
packet-stream.rb:147:in `synchronize'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
packet-stream.rb:147:in `get'
        from /usr/local/lib/ruby/site_ruby/1.8/needle/lifecycle/
proxy.rb:60:in `__send__'
        from /usr/local/lib/ruby/site_ruby/1.8/needle/lifecycle/
proxy.rb:60:in `method_missing'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
session.rb:247:in `wait_for_message'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
session.rb:242:in `loop'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/transport/
session.rb:242:in `wait_for_message'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/connection/
driver.rb:148:in `process'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/connection/
driver.rb:138:in `loop'
        from /usr/local/lib/ruby/site_ruby/1.8/net/ssh/session.rb:
164:in `loop'

Could anyone give me a hint?

2

Hi,

do you have installed the ruby openssl bindings?

Andre

···

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3

Saga,

There are many ways to execute commands via the NET::SSH. Here is one
option that will do what you want it to do:

This encapsulates the commands:
Net::SSH.start(h,u,p) do |session|
  shell = session.shell.sync
    cmd = shell.send_command "whatevercommand\n"
    p cmd.stdout
    cmd2 = shell.send_command "whatevercommand\n"
    p cmd2.stdout
  end
end

Or, if it's a standard command, you can do this:
Net::SSH.start(h,u,p) do |session|
  shell = session.shell.sync
    cmd = shell.whatevercommand
    p cmd.stdout
    cmd2 = shell.whatevercommand
    p cmd2.stdout
  end
end

Cool thing about this is, if you are running a command that pipes to
stderr, you can also capture that with cmd.stderr.

Using the shell.send_command method allows you to send entire strings
to be executed, such as:

cmd = shell.send_command("cat /proc/partitions")
p cmd.stdout

Which allows you to capture the stdout as a string, then parse it as
such:

cmd = shell.send_command("cat /proc/partitions")
devices = out.stdout
devices.gsub!(/\n/,'')
devices.gsub!(/([0123456789])/, '')
disks<<devices.scan(%r/ (.*) /)
puts disks.uniq!

Which "should" give you a list of all unique mounted drives in your
system... just as an example.

Hope this helps,
Caveman

4

The ssh authentication works fine. Login to the remote host
successfully. I assume the openssl binding are installed.

···

On May 10, 5:12 pm, Andre Ferreira <alf...@gmail.com> wrote:

Hi,

do you have installed the ruby openssl bindings?

Andre

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