VB.NET

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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Dim success As Boolean = 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.

Dim ssh As New Chilkat.Ssh

Dim sshPort As Integer = 22
success = ssh.Connect("ssh.example.com",sshPort)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  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.
Dim password As String = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Open a session channel.  A negative return value indicates failure.
Dim channelNum As Integer = ssh.OpenSessionChannel()
If (channelNum < 0) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Set environment variables for the channel.  Multiple variables may be requested.
success = ssh.SendReqSetEnv(channelNum,"LANG","en_US.UTF-8")
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


success = ssh.SendReqSetEnv(channelNum,"MY_APP_MODE","production")
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Now run the command, which sees the requested environment.
success = ssh.SendReqExec(channelNum,"echo $MY_APP_MODE")
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  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.ReadTimeoutMs = 15000

success = ssh.ChannelReceiveToClose(channelNum)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


Dim output As String = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If

Debug.WriteLine(output)

ssh.Disconnect()