PowerShell 2.0 – Introducing the PModem File Transfer Protocol

One of the things that never quite fit well with me with the remoting feature in PowerShell 2.0 is that while you can “telnet” to remote systems with Enter-PSSession and import commands and do all sorts of cool tricks, there is no way to send or retrieve files from the console. It seems like such a waste that you configure WinRM up with SSL and Kerberos and get this nice encrypted channel up, but if you want to transfer files you have to revert to file shares, remote desktop or classic ftp.

Back in the “good ole’ days” of BBSs and FidoNet, people used to use simple protocols like XModem (advancing to YModem and then ZModem) or Kermit that worked by streaming character data directly to your terminal. It wasn’t fast or particularly efficient, but it got the job done. I thought I’d take a crack at building something similar for PowerShell, and this first 0.5 release is the fruits of this weekend’s tinkering. At the moment it only can “pull” a file to the local system from a remote session, but the next release will allow “pushing” a file from a local system to a remote session.

image

The reason I named it after XModem is because it works in a similar way: files are not “pulled” from the remote server, but instead are “pushed.” X[YZ]Modem file transfer was initiated by the remote end. I’ll not spoil the fun by explaining how it works, but I think you’ll enjoy pulling it apart. It’s in a module format and is implemented in pure script.

Requirements

  • PowerShell 2.0 installed on both client and server with remoting enabled to the location of the file being transferred.

E.g. if you want to grab a file using Get-RemoteFile from a remote server, you must be able to create a valid PSSession to it with the New-PSSession cmdlet. When Send-LocalFile is implemented, you’ll need remoting enabled in the other direction too.

  • The PMODEM module must be findable on both the client and server via import-module and must be the same version.

Here’s the Get-RemoteFile function help (via –?):

NAME
    Get-RemoteFile

SYNOPSIS
    Retrieves a file from a remote computer via a supplied PSession.


SYNTAX
    Get-RemoteFile [-Session] <pssession> [-RemoteFile] <string> [[-LocalPath] <string>] [[-PacketSize] <int32>]
	[-PassThru] [-AsJob] [<commonparameters>]


DESCRIPTION
    Retrieves a remote file from a server via a supplied PSSession. All communication
    is performed out-of-band, yet inside the secure WinRM channel.

    No other ports, file shares or any other special configuration is needed. However,
    the PMODEM module must be on the remote computer and findable in its $ENV:PSModulePath;
    the protocol versions must also match on both ends. You will be warned of any
    misconfiguration(s).

    When not running asynchronously, progress records are generated.


RELATED LINKS

REMARKS
    To see the examples, type: "get-help Get-RemoteFile -examples".
    For more information, type: "get-help Get-RemoteFile -detailed".
    For technical information, type: "get-help Get-RemoteFile -full".

Things coming in later releases: wildcards/multiple file support, compression and integration via proxy functions (copy-item/move-item/remove-item/rename-item etc).

Download PModem

Grab pmodem-0.5.zip and unzip it into a folder in your $ENV:PSModulePath on the client and server computers you want to use PMODEM on.

Have fun!

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About the author

Irish, PowerShell MVP, .NET/ASP.NET/SharePoint Developer, Budding Architect. Developer. Montrealer. Opinionated. Montreal, Quebec.

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