VBScript

SSH Commands that Prompt for Input, such as su

Demonstrates running a shell command that prompts for additional input, using su as the example. The technique is: send the command, read until the expected prompt appears, then send the response exactly as though it were typed.

Note: This example deliberately requests a PTY. su reads its password from a controlling terminal and refuses to run without one, so a pseudo-terminal is genuinely required here.

Background: Programs that ask for a password almost always insist on reading it from a real terminal rather than a pipe — a deliberate safeguard against passwords being fed in by scripts. That is why this is one of the cases where a PTY is necessary despite the general advice to avoid one. The interaction is a strict send-then-read-to-prompt cycle, and retrieving the received text between steps is essential: a prompt left in the buffer would make the next receive return immediately with the wrong output. Where possible, a passwordless sudo rule avoids this dance altogether.

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VBScript

Dim fso, outFile
Set fso = CreateObject("Scripting.FileSystemObject")
'Create a Unicode (utf-16) output text file.
Set outFile = fso.CreateTextFile("output.txt", True, True)

success = 0

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

'  Demonstrates running a shell command that prompts for additional input, using "su" as the
'  example.  The technique is: send the command, read until the expected prompt, then send the
'  response as though it were typed.
'  
'  Note: This example deliberately DOES request a PTY.  "su" reads its password from a
'  controlling terminal and refuses to run without one, so a pseudo-terminal is required here.

set ssh = CreateObject("Chilkat.Ssh")

hostname = "ssh.example.com"
port = 22
success = ssh.Connect(hostname,port)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
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.
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

channelNum = ssh.OpenSessionChannel()
If (channelNum < 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

'  Request a pseudo-terminal.  A "dumb" terminal avoids ANSI escape sequences in the output.
termType = "dumb"
widthInChars = 120
heightInChars = 40
pixWidth = 0
pixHeight = 0
success = ssh.SendReqPty(channelNum,termType,widthInChars,heightInChars,pixWidth,pixHeight)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

success = ssh.SendReqShell(channelNum)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

'  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.ReadTimeoutMs = 15000

caseSensitive = 1

'  Send the su command.  Linux/UNIX servers generally expect a bare LF, not a CRLF.
success = ssh.ChannelSendString(channelNum,"su" & vbLf,"utf-8")
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

'  Read until su prompts for the password.
success = ssh.ChannelReceiveUntilMatch(channelNum,"Password:","utf-8",caseSensitive)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

outFile.WriteLine(cmdOutput)

'  Send the root password, exactly as if it were typed at the prompt.  Like the login password,
'  this should come from a secure source rather than being hard-coded.
suPassword = "myRootPassword"
success = ssh.ChannelSendString(channelNum,suPassword,"utf-8")
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

success = ssh.ChannelSendString(channelNum,vbLf,"utf-8")
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

'  Read the response up to the root shell prompt.  This will differ on your system.
myShellPrompt = "root@myserver:~#"
success = ssh.ChannelReceiveUntilMatch(channelNum,myShellPrompt,"utf-8",caseSensitive)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

'  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
'  buffered, the next receive would match it immediately.
cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

outFile.WriteLine(cmdOutput)

'  Now run a command as root.
success = ssh.ChannelSendString(channelNum,"ls" & vbLf,"utf-8")
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

success = ssh.ChannelReceiveUntilMatch(channelNum,myShellPrompt,"utf-8",caseSensitive)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

outFile.WriteLine(cmdOutput)

'  Additional commands follow the same pattern: send the command, read to the next prompt, then
'  fetch and clear the receive buffer.

success = ssh.ChannelSendEof(channelNum)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

success = ssh.ChannelSendClose(channelNum)
If (success = 0) Then
    outFile.WriteLine(ssh.LastErrorText)
    WScript.Quit
End If

ssh.Disconnect 

outFile.Close