Getting ssh-agent going on Mac OSX

It seems irritating that OSX doesn't have an easy way to get ssh-agent running for a login session. However it can be done using launchd and a bit of scripting.

Before you start you'll need to have an /Users/username/.ssh directory (where username is your username) - or alter the scripts appropriately below. Create file /Users/username/Library/LaunchAgents/ssh-agent.plist containing:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Label</key>
<string>com.ssh.ssh-agent</string>
<key>OnDemand</key>
<false/>
<key>Program</key>
<string>/Users/username/.ssh/ssh-agent.sh</string>
<key>RunAtLoad </key>
<true/>
<key>ServiceDescription</key>
<string>Launch ssh-agent</string>
</dict></plist>

Then create a file /Users/username/.ssh/ssh-agent.sh containing:
#!/bin/sh
rm /Users/username/.ssh/ssh-agent.pipe
exec /usr/bin/ssh-agent -a /Users/username/.ssh/ssh-agent.pipe -d

Note: ssh-agent has to be started using -d option as launchd doesn't like processes to fork off into 'daemons'...probably why a few people don't like it.

Make the script executable:
$ chmod +x /Users/username/.ssh/ssh-agent.sh

Then ssh-agent will get started next time you login by launchd, or you can start it immediately by running:
$ launchctl start com.ssh.ssh-agent

Now you need to set the following environment variable (you can use RCEnvironment to set ~/.MacOSX/environment.plist) - probably easiest to add the following line to your /Users/username/.profile:
export SSH_AUTH_SOCK=/Users/username/.ssh/ssh-agent.pipe

You can then add your keys (assuming you've set 'em up using ssh-keygen or whatever) to the agent using:
$ ssh-add