B4X

SSH ChannelReceiveUntilMatchN (Match Any of Several Prompts)

Demonstrates ChannelReceiveUntilMatchN, which receives until any one of several patterns is matched. This is useful when driving an interactive session where the shell prompt differs from device to device.

Note: This example deliberately requests a PTY. Matching a shell prompt only works in an interactive session — without a PTY the shell runs non-interactively and never prints a prompt at all. For scripted use, omit the PTY and match on a marker your own command echoes.

Background: Real sessions have more than one possible next output, so waiting for one specific string risks hanging when something else appears. Matching a set lets the code proceed on whichever actually occurs — a user prompt, a root prompt, or a device-specific one. A "dumb" terminal type is requested so the remote side does not mix ANSI escape sequences into the output, which would otherwise complicate matching. Remember that retrieving text clears the receive buffer; leaving a prompt buffered would make the next receive match immediately and return the wrong output.

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Dim success As Boolean = False

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

'  Demonstrates ChannelReceiveUntilMatchN, which receives until ANY one of several patterns is
'  matched.  This is useful when driving an interactive session where the shell prompt varies
'  from device to device.
'  
'  Note: This example deliberately DOES request a PTY.  Matching a shell prompt only works in an
'  interactive session -- without a PTY the shell runs non-interactively and never prints a
'  prompt at all.  For scripted use where no prompt is needed, omit the PTY and match on a
'  marker your own command echoes instead.

Dim ssh As ChilkatSsh
ssh.Initialize("ssh")

'  The remote shell prompt may be any of these, depending on the device.
Dim saPrompts As ChilkatStringArray
saPrompts.Initialize
saPrompts.Append("~$")
saPrompts.Append("mars#")
saPrompts.Append("jupiter%")
saPrompts.Append("chilkat$")
saPrompts.Append("admin>")

Dim hostname As String = "ssh.example.com"
Dim port As Int = 22
success = ssh.Connect(hostname, port)
If success = False Then
    Log(ssh.LastErrorText)
    Return
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
    Log(ssh.LastErrorText)
    Return
End If


Dim channelNum As Int = ssh.OpenSessionChannel
If channelNum < 0 Then
    Log(ssh.LastErrorText)
    Return
End If


'  Request a pseudo-terminal so the shell runs interactively and prints prompts.  A "dumb"
'  terminal is used so that ANSI escape sequences are not mixed into the output.
Dim termType As String = "dumb"
Dim widthInChars As Int = 120
Dim heightInChars As Int = 40
Dim pixWidth As Int = 0
Dim pixHeight As Int = 0
success = ssh.SendReqPty(channelNum, termType, widthInChars, heightInChars, pixWidth, pixHeight)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.SendReqShell(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
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

Dim caseSensitive As Boolean = True

'  Read the initial login text up to the first prompt.
success = ssh.ChannelReceiveUntilMatchN(channelNum, saPrompts, "utf-8", caseSensitive)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


Dim cmdOutput As String = ssh.GetReceivedText(channelNum, "utf-8")
If ssh.LastMethodSuccess = False Then
    Log(ssh.LastErrorText)
    Return
End If

Log(cmdOutput)

'  ---- 1st command ----
success = ssh.ChannelSendString(channelNum, "cd /tmp" & Chr(10), "utf-8")
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.ChannelReceiveUntilMatchN(channelNum, saPrompts, "utf-8", caseSensitive)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


'  Retrieving the text also clears the receive buffer, which matters: if a prompt were left
'  buffered, the next receive would match it immediately and return the wrong output.
cmdOutput = ssh.GetReceivedText(channelNum, "utf-8")
If ssh.LastMethodSuccess = False Then
    Log(ssh.LastErrorText)
    Return
End If

Log(cmdOutput)

'  ---- 2nd command ----
success = ssh.ChannelSendString(channelNum, "ls" & Chr(10), "utf-8")
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.ChannelReceiveUntilMatchN(channelNum, saPrompts, "utf-8", caseSensitive)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


cmdOutput = ssh.GetReceivedText(channelNum, "utf-8")
If ssh.LastMethodSuccess = False Then
    Log(ssh.LastErrorText)
    Return
End If

Log(cmdOutput)

'  Finish the session.
success = ssh.ChannelSendEof(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


success = ssh.ChannelReceiveToClose(channelNum)
If success = False Then
    Log(ssh.LastErrorText)
    Return
End If


cmdOutput = ssh.GetReceivedText(channelNum, "utf-8")
If ssh.LastMethodSuccess = False Then
    Log(ssh.LastErrorText)
    Return
End If

Log(cmdOutput)

ssh.Disconnect