CkPython

Set an Environment Variable on an SSH Channel

Demonstrates the Chilkat Ssh.SendReqSetEnv method, which asks the server to set an environment variable for a session channel. The arguments are the channel number, the variable name, and its value. Send these requests before the exec, shell, or subsystem request.

Background: This is the clean way to pass configuration to a remote command without embedding it in the command line. Be aware that many SSH servers restrict which variables clients may set (OpenSSH's AcceptEnv), so a request can be silently ignored or rejected — do not rely on it without verifying the server's policy.

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import sys
import chilkat

success = False

#  Demonstrates the Ssh.SendReqSetEnv method, which asks the server to set an environment
#  variable for a session channel.  The 1st argument is the channel number, the 2nd is the
#  variable name, and the 3rd is its value.  Send it before the exec, shell, or subsystem
#  request.

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()

#  Open a session channel.  A negative return value indicates failure.
channelNum = ssh.OpenSessionChannel()
if (channelNum < 0):
    print(ssh.lastErrorText())
    sys.exit()

#  Set environment variables for the channel.  Multiple variables may be requested.
success = ssh.SendReqSetEnv(channelNum,"LANG","en_US.UTF-8")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

success = ssh.SendReqSetEnv(channelNum,"MY_APP_MODE","production")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  Now run the command, which sees the requested environment.
success = ssh.SendReqExec(channelNum,"echo $MY_APP_MODE")
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

#  IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
#  it, this call waits forever if the server never sends channel close.
ssh.put_ReadTimeoutMs(15000)

success = ssh.ChannelReceiveToClose(channelNum)
if (success == False):
    print(ssh.lastErrorText())
    sys.exit()

output = ssh.getReceivedText(channelNum,"utf-8")
if (ssh.get_LastMethodSuccess() == False):
    print(ssh.lastErrorText())
    sys.exit()

print(output)

ssh.Disconnect()