There are some of us out there that use appliances, equipment, or software that is still stuck with the telnet protocol. Where there are options for scripting interactions with webpages, SSH, and many other resources, I did not find many options for telnet scripting, and I'm not at the point in powershell where I could whip up a telnet client in powershell. Fortunately,
Grant Carthew has already done the heavy lifting here. Below you can find a modified version of his script that allows scripting interactions through the telnet protocol, retrieving the responses so that logic can be performed on them.
Credits to the
Ugly Gizmo blog, this script would not be without Grant's work.
<#
.SYNOPSIS
A modified graceful telnet scripting client using PowerShell and the .NET Framework.
.DESCRIPTION
This script was originally made with a view of using it to have full control over the text
stream for automating Cisco router and switch configurations. Modifications have been
added for scripting automation and logic
.PARAMETER TelnetHost
The address of the server or router hosting the telnet service.
.PARAMETER Port
The TCP port number of the Telnet service running on the Telnet host.
.NOTES
Modified: http://garcol.blogspot.com/2014/07/powershell-scripting-telnet.html
Original: http://uglygizmo.blogspot.com/2013/10/a-telnet-client-written-in-powershell.html
#>
param
(
[parameter(Mandatory)]
[String]
$TelnetHost,
[Int]
$TelnetPort = 23
)
# Initialize variables
[System.Text.ASCIIEncoding]$ASCIIEncoding = [System.Text.Encoding]::ASCII
[System.Net.Sockets.Socket]$Socket = $null
# Checking host address and port.
if ($TelnetHost -match ":")
{
$hostBytes = $TelnetHost.Split(':')
$TelnetHost = $hostBytes[0]
$TelnetPort = $hostBytes[1]
}
if ([String]::IsNullOrEmpty($TelnetHost))
{
Write-Host -Object "Error: Invalid host address (null or empty)." -ForegroundColor Red
return
}
# Setup and connect the TCP Socket.
$Socket = New-Object -TypeName System.Net.Sockets.Socket(
[System.Net.Sockets.AddressFamily]::InterNetwork,
[System.Net.Sockets.SocketType]::Stream,
[System.Net.Sockets.ProtocolType]::Tcp)
$Socket.NoDelay = $true
try
{
$Socket.Connect($TelnetHost, $TelnetPort)
}
catch
{
"Unable to connect to host {0}:{1}" -f $TelnetHost,$TelnetPort
return
}
# This state object is used to pass the connected Socket and the
# PowerShell parent Host reference to the child PowerShell object.
$State = [PSCustomObject]@{"Socket"=$Socket;"Host"=$Host;"Exception"=$null;"Response"=$null}
# This script block is used as the receive code for the Socket
# from within the child PowerShell object.
$Script = {
param($state)
[string[]]$returnLog = "Started"
# This encoding object is used to decode the return string.
[System.Text.ASCIIEncoding]$ASCIIEncoding = [System.Text.Encoding]::ASCII
# TELNET commands
[Byte]$GA = 249 # Go Ahead
[Byte]$WILL = 251 # Desire to begin
[Byte]$WONT = 252 # Refusal to perform
[Byte]$DO = 253 # Request that the other party perform
[Byte]$DONT = 254 # Demand that the other party stop performing
[Byte]$IAC = 255 # Interpret as Command
# TELNET options
[Byte]$ECHO = 1 # Used to check the echo mode
[Byte]$SUPP = 3 # Suppress go ahead
# Used to hold the number of bytes returned from the network stream.
[Int]$bytes = 0
# Buffer to hold the returned Bytes.
[Byte[]]$buffer = New-Object -TypeName Byte[]($state.Socket.ReceiveBufferSize)
# This is the main receive loop.
while ($state.Socket.Connected)
{
try
{
# The following statement will block the thread until data is received.
$bytes = $state.Socket.Receive($buffer)
}
catch
{
# This exception reference is used to pass the error back to the
# parent PowerShell process.
$state.Exception = $Error[0]
break
}
if ($bytes -gt 0)
{
$index = 0
$responseLen = 0
# The index is used to move through the buffer to analyze the received data
# looking for Telnet commands and options.
while ($index -lt $bytes)
{
if ($buffer[$index] -eq $IAC)
{
try
{
switch ($buffer[$index + 1])
{
# If two IACs are together they represent one data byte 255
$IAC
{
$buffer[$responseLen++] = $buffer[$index]
$index += 2
break
}
# Ignore the Go-Ahead command
$GA
{
$index += 2
break
}
# Respond WONT to all DOs and DONTs
{($_ -eq $DO) -or ($_ -eq $DONT)}
{
$buffer[$index + 1] = $WONT
$state.Socket.Send($buffer, $index, 3,
[System.Net.Sockets.SocketFlags]::None) | Out-Null
$index += 3
break
}
# Respond DONT to all WONTs
$WONT
{
$buffer[$index + 1] = $DONT
$state.Socket.Send($buffer, $index, 3,
[System.Net.Sockets.SocketFlags]::None) | Out-Null
$index += 3
break
}
# Respond DO to WILL ECHO and WILL SUPPRESS GO-AHEAD
# Respond DONT to all other WILLs
$WILL
{
[Byte]$action = $DONT
if ($buffer[$index + 2] -eq $ECHO)
{
$action = $DO
}
elseif ($buffer[$index + 2] -eq $SUPP)
{
$action = $DO
}
$buffer[$index + 1] = $action
$state.Socket.Send($buffer, $index, 3,
[System.Net.Sockets.SocketFlags]::None) | Out-Null
$index += 3;
break;
}
}
}
catch
{
# If there aren't enough bytes to form a command, terminate the loop.
$index = $bytes
}
}
else
{
if ($buffer[$index] -ne 0)
{
$buffer[$responseLen++] = $buffer[$index]
}
$index++
}
}
# Displays the response with no command codes on the parent PowerShell object.
$returnString = $ASCIIEncoding.GetString($buffer, 0, $responseLen)
$returnLog += $returnString
#$state.Host.UI.Write($returnString)
$state.response += $returnString
}
}
} # End of the child PowerShell script definition.
# Create a child PowerShell object to run the background Socket receive method.
$PS = [PowerShell]::Create()
$PS.AddScript($Script).AddArgument($State) | Out-Null
[System.IAsyncResult]$AsyncJobResult = $null
try
{
# The receive job is started asynchronously.
$AsyncJobResult = $PS.BeginInvoke()
#YOUR TELNET COMMANDS IN HERE
# Sends Commands
function sendCmd($command)
{
# Wait, then send data.
start-sleep -m 500
$Data = $ASCIIEncoding.GetBytes($command)
$Socket.Send($Data) | Out-Null
$Socket.Send(13) | Out-Null #sends the return keystroke after each cmd
start-sleep -m 500
}
######################################################################################
#TELNET COMMANDS IN HERE
# Use sendCmd("") to send text commands, use $Socket.Send() to send ascii encoded keystrokes
#
# List of Commands to be Sent
[string[]]$cmdList = "username"
$cmdlist += "password"
# Login
foreach ($cmd in $cmdlist){ sendCmd($cmd) | out-null}
sendCmd("show something") | out-null
$thisData = $state.response #Can perform logic on the response here
$state.response = $null
# Issue the Exit command, closing the session gracefully
sendCmd("exit") | out-null
#
#TELNET COMMANDS IN HERE
######################################################################################
}
finally
{
# Cleanup the socket and child PowerShell process.
if ($Socket -ne $null)
{
$Socket.Close()
$Socket.Dispose()
$Socket = $null
}
if ($PS -ne $null -and $AsyncJobResult -ne $null)
{
$PS.EndInvoke($AsyncJobResult)
$PS.Dispose()
}
}
