CkPython

Get Received SSH Text Up To a Substring

Demonstrates the Chilkat Ssh.GetReceivedTextS method, which searches the receive buffer for a literal, case-sensitive substring. The arguments are the channel number, the substring, and the charset. If found, everything through and including the first occurrence is returned and removed; if not found, an empty string is returned successfully and the buffer is left unchanged.

Background: This gives you a consuming read up to a delimiter, which is how you carve a continuous shell stream into discrete responses — echo a marker after each command, then pull exactly the text through that marker and leave anything that arrived afterward for the next round. Note an empty substring is invalid and fails without consuming the buffer.

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import sys
import chilkat

success = False

#  Demonstrates the Ssh.GetReceivedTextS method, which searches the receive buffer for a literal
#  substring.  The 1st argument is the channel number, the 2nd is the substring, and the 3rd is
#  the charset.  If found, everything through and including the first occurrence is returned and
#  removed from the buffer.

ssh = chilkat.CkSsh()

sshPort = 22
success = ssh.Connect("ssh.example.com",sshPort)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  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())
    sys.exit()

channelNum = ssh.OpenSessionChannel()
if (channelNum < 0):
    print(ssh.lastErrorText())
    sys.exit()

#  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())
    sys.exit()

success = ssh.ChannelSendString(channelNum,"echo BEGIN; ls /tmp; echo END_MARKER\n","utf-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

pollTimeoutMs = 1000
result = ssh.ChannelReadAndPoll(channelNum,pollTimeoutMs)
if (result == -1):
    print(ssh.lastErrorText())
    sys.exit()

#  Return everything up through the marker.  If the marker is not present, an empty string is
#  returned successfully and the buffer is left unchanged.
upToMarker = ssh.getReceivedTextS(channelNum,"END_MARKER","utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(upToMarker)

ssh.Disconnect()