Windows, SSH Agent, and Emacs

Because I’m a sick sort of puppy, I work in Emacs on Windows for basic text editing and especially for working with Git (Magit is the best), and use Powershell (and Posh-git) for my shell. However, if I launch Emacs from a pinned shortcut on my taskbar instead of from within a Powershell session, I don’t get access to ssh-agent, which puts a bit of a damper on actually working with Git.

As it turns out, the Magit team has already mostly solved this problem – they modified GitHub’s ssh-agent start script to emit a small piece of Emacs Lisp that sets the SSH_AUTH_SOCK and SSH_AGENT_PID environment variables using the setenv function. Here’s that code ported to Powershell:

# Write the SSH agent environment variables so that emacs can pick them up
$agentVarsFile = "$env:USERPROFILE\Dropbox\.emacs.d\ssh-agent-vars.el"
# Truncate the file first
Set-Content $agentVarsFile $null
# Now add to it
Add-Content $agentVarsFile ("(setenv `"SSH_AGENT_PID`" `"{0}`")" -f $env:SSH_AGENT_PID)
Add-Content $agentVarsFile ("(setenv `"SSH_AUTH_SOCK`" `"{0}`")" -f $env:SSH_AUTH_SOCK)

You should change the path to suit your needs – I keep my .emacs.d folder in Dropbox and symlink it into place, so I chose the direct path approach. This code sits in my Powershell profile directly after the Posh-git bits are loaded and ssh-agent is started (or is already running). Then, all that’s necessary is to add a bit of code to my Emacs init.el:

(load-file "~/.emacs.d/ssh-agent-vars.el")

Now, Emacs will load that file when it starts – as long as ssh-agent is running before Emacs is started, it’ll work fine. If it’s not, I can always re-evaluate that bit of Elisp and get the environment loaded after the fact.