VB.NET

SSH Exec (Execute Command Line)

Demonstrates running a single command on an SSH server with an exec request and retrieving its output. The example connects, authenticates, opens a session channel, sends the command, reads until the server closes the channel, and then checks the exit status.

Background: exec is the workhorse of SSH automation: it runs one command and the server closes the channel when the command exits, which is a definitive end-of-output signal. No PTY is involved, so the shell runs non-interactively — no prompt, no echoed input, no ANSI escape codes — giving clean, parseable output. Remember that an accepted exec request only means the request was accepted; the command's own success is reported through the channel exit status. Command syntax depends on the remote shell, which is the user's default shell on Linux/UNIX and usually CMD.EXE on Windows SSH servers.

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VB.NET

Dim success As Boolean = False

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

'  Demonstrates running a single command on an SSH server with an exec request and retrieving
'  its output.  An exec request runs one command and the server closes the channel when it
'  finishes -- no PTY and no shell prompt are involved, so the output is clean and parseable.

Dim ssh As New Chilkat.Ssh

'  The hostname may be a hostname or an IP address.
Dim hostname As String = "ssh.example.com"
Dim port As Integer = 22
success = ssh.Connect(hostname,port)
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.  Several session channels may be open at once on one connection.
Dim channelNum As Integer = ssh.OpenSessionChannel()
If (channelNum < 0) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  The command syntax depends on the remote system's shell.  On Linux/UNIX it is typically the
'  user's default shell; on Windows SSH servers it is usually CMD.EXE.
'    Linux/UNIX:  "ls -l /tmp"        or  "cd /etc; ls -la"
'    Windows:     "dir"               or  "\"cd \\temp&&dir\""
success = ssh.SendReqExec(channelNum,"ls -l /tmp")
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

'  Read the output until the server sends channel close, which happens when the command exits.
success = ssh.ChannelReceiveToClose(channelNum)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


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

Debug.WriteLine(cmdOutput)

'  An accepted exec request does not mean the command succeeded.  Check the exit status.
If (ssh.ChannelReceivedExitStatus(channelNum)) Then
    Debug.WriteLine("Exit status: " & ssh.GetChannelExitStatus(channelNum))
End If


ssh.Disconnect()