Is there a way to send character strings between 2 powershell terminal windows?

In unix world we have always been able to send character strings between terminal windows using the /dev/ttyS serial devices or the /dev/pty pseudo-terminals. To do that is trivial once you know your tty/pty number, and could use:

# On /dev/pty1 write:
echo -e "\nHello! \n" >/dev/pty0

# On /dev/pty0, receive:

Hello! 

_{(There is a bug in the Cygwin/Bash version that interferes with the character \n and whatever is in front, unless its a space.)}

This even works in MSYS/Cygwin.

Is there a way to accomplish a way to do the same (in Windows) between powershell terminal windows?

I have seen that you can send strings using the COM serial devices, using something like:

echo "Hello!" > \\.\COM3\

But AFAIK, the Windows terminal shell doesn't have an associated COM port, nor anything else obvious or accessible.

Apparently the COM ports are set in the registry at:
HKLM:\SYSTEM\CurrentControlSet\Control\COM Name Arbiter\Devices

References:

• https://devblogs.microsoft.com/commandline/windows-command-line-introducing-the-windows-pseudo-console-conpty/#what-no-windows-pseudo-console

• https://learn.microsoft.com/en-us/windows/console/creating-a-pseudoconsole-session

The closest I could think is to use NamedPipeServerStream and NamedPipeClientStream as suggested in this answer, however the difference here is that your server is started on a different thread and writes to your console using PSConsoleReadLine.Insert, this provides similar functionality as what you have in the Linux word.

Here you can see how to use these functions:

You can also pipe to the writing function, so something like this can work:

PS \> Get-Content foo.txt | pipemsg theDestinationPipe

You should note using PSConsoleReadLine.Insert like this is a bit wonky and outside the supported realm.

Lastly, the Start-NamedPipeServer function outputs an object that can be used as argument to Remove-NamedPipeServer. Once you're done using your server you can dispose it like this:

# create
$server = Start-NamedPipeServer myServer
# dispose
$server | Remove-NamedPipeServer

Here is the function definitions:

function Start-NamedPipeServer {
    [Alias('pipeserver')]
    param(
        [Parameter(Mandatory)]
        [string] $Name
    )

    if ([System.IO.File]::Exists("\\.\pipe\$Name")) {
        $err = [System.Management.Automation.ErrorRecord]::new(
            [System.IO.IOException]::new("A pipe already exists with name '$Name'."),
            'PipeExists',
            [System.Management.Automation.ErrorCategory]::OpenError,
            $null)

        $PSCmdlet.ThrowTerminatingError($err)
    }

    $script = {
        while (-not $token.IsCancellationRequested) {
            try {
                $pipe = [System.IO.Pipes.NamedPipeServerStream]::new(
                    $Name, [System.IO.Pipes.PipeDirection]::InOut, 1,
                    [System.IO.Pipes.PipeTransmissionMode]::Byte,
                    [System.IO.Pipes.PipeOptions]::Asynchronous)

                $task = $pipe.WaitForConnectionAsync($token)
                while (-not $task.AsyncWaitHandle.WaitOne(200)) { }
                $null = $task.GetAwaiter().GetResult()
                $sr = [System.IO.StreamReader]::new($pipe)
                while ($null -ne ($msg = $sr.ReadLine())) {
                    [Microsoft.PowerShell.PSConsoleReadLine]::Insert($msg + "`n")
                }
            }
            catch [System.OperationCanceledException] {
                # ignore
            }
            finally {
                if ($pipe) { $pipe.Dispose() }
                if ($sr) { $sr.Dispose() }
            }
        }
    }

    $src = [System.Threading.CancellationTokenSource]::new()
    $ps = [powershell]::Create().AddScript($script)
    $ps.Runspace.SessionStateProxy.SetVariable('Name', $Name)
    $ps.Runspace.SessionStateProxy.SetVariable('token', $src.Token)

    [pscustomobject]@{
        TokenSource = $src
        Instance    = $ps
        Async       = $ps.BeginInvoke()
    }
}

function Write-PipeMessage {
    [Alias('pipemsg')]
    param(
        [Parameter(Mandatory)]
        [string] $Name,

        [Parameter(ValueFromPipeline, ValueFromRemainingArguments)]
        [string[]] $Message
    )

    begin {
        try {
            $pipe = [System.IO.Pipes.NamedPipeClientStream]::new($Name)
            $task = $pipe.ConnectAsync()
            while (-not $task.Wait(200)) { }
            $sw = [System.IO.StreamWriter]::new($pipe)
        }
        catch {
            $PSCmdlet.ThrowTerminatingError($_)
        }
    }
    process {
        foreach ($msg in $Message) {
            $sw.WriteLine($msg)
        }
    }
    end {
        $sw.Dispose()
        $pipe.Dispose()
    }
}

function Remove-NamedPipeServer {
    param([Parameter(Mandatory, ValueFromPipeline)] $Server)

    process {
        try {
            $Server.TokenSource.Cancel()
            $Server.TokenSource.Dispose()
            $Server.Instance.EndInvoke($Server.Async)
            if ($Server.Instance.HadErrors) {
                foreach ($err in $Server.Instance.Streams.Error) {
                    $PSCmdlet.WriteError($err)
                }
            }
            $Server.Instance.Dispose()
        }
        catch {
            $PSCmdlet.WriteError($_)
        }
    }
}