Ruby

SSH Remote Shell with Multiple Commands

Demonstrates running several commands one after another in a single remote shell session, retrieving each command's output separately. No PTY is requested, so each command is followed by an echoed marker that signals where its output ends.

Background: Interleaving commands and reads in one shell requires a way to know where each command's output stops. An interactive session would use the shell prompt, but without a PTY the shell is non-interactive and never prints one — so the dependable technique is to append echo SOME_MARKER to each command and read up to that marker. Retrieving the text also clears the receive buffer, which matters here: if a marker were left buffered, the next receive would match it immediately and return the wrong output.

Chilkat Ruby Downloads

Download Chilkat for Ruby

Ruby

require 'chilkat'

success = false

#  This example requires the Chilkat API to have been previously unlocked.
#  See Global Unlock Sample for sample code.

#  Demonstrates running several commands one after another in a single remote shell session,
#  retrieving each command's output separately.
#  
#  No PTY is requested, so the shell runs non-interactively and never prints a command prompt.
#  Because there is no prompt to synchronize on, each command is followed by an "echo" of a
#  unique marker, and the output is read up to that marker.

ssh = Chilkat::CkSsh.new()

hostname = "ssh.example.com"
port = 22
success = ssh.Connect(hostname,port)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  Normally you would not hard-code the password in source.  You should instead obtain it
#  from an interactive prompt, environment variable, or a secrets vault.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

channelNum = ssh.OpenSessionChannel()
if (channelNum < 0)
    print ssh.lastErrorText() + "\n";
    exit
end

#  Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
#  raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
#  echo typed commands back, and skips interactive login scripts.  The output is therefore
#  clean and easily parseable -- but because no prompt is ever sent, code must not wait for
#  one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
success = ssh.SendReqShell(channelNum)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
#  which means no limit -- without it, this call waits forever if the received data never
#  contains a match.
ssh.put_ReadTimeoutMs(15000)

caseSensitive = true

#  ---- 1st command: change directory ----
success = ssh.ChannelSendString(channelNum,"cd /tmp; echo END_OF_CMD_1\n","utf-8")
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

success = ssh.ChannelReceiveUntilMatch(channelNum,"END_OF_CMD_1","utf-8",caseSensitive)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  Retrieving the text also clears the receive buffer, which matters: if the next marker were
#  left in the buffer, the following receive would match immediately.
cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == false)
    print ssh.lastErrorText() + "\n";
    exit
end

print cmdOutput + "\n";

#  ---- 2nd command: directory listing ----
success = ssh.ChannelSendString(channelNum,"ls; echo END_OF_CMD_2\n","utf-8")
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

success = ssh.ChannelReceiveUntilMatch(channelNum,"END_OF_CMD_2","utf-8",caseSensitive)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == false)
    print ssh.lastErrorText() + "\n";
    exit
end

print cmdOutput + "\n";

#  ---- 3rd command: long listing, then finish the session ----
success = ssh.ChannelSendString(channelNum,"ls -l\n","utf-8")
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

#  No more input will be sent.
success = ssh.ChannelSendEof(channelNum)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

success = ssh.ChannelReceiveToClose(channelNum)
if (success == false)
    print ssh.lastErrorText() + "\n";
    exit
end

cmdOutput = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == false)
    print ssh.lastErrorText() + "\n";
    exit
end

print cmdOutput + "\n";

ssh.Disconnect()