Starting an ssh-agent once and restoring the session later. A really lightweight version of the `keychain` script.

ssh-agent.sh

# A function which restarts the ssh-agent, saves the output to a file which can
# be sourced later, and adds the default ssh key.
sshenv=$HOME/.sshlocal
function init-ssh-agent() {
    # Kill the agent if it's running.
    if [ -n "$SSH_AGENT_PID" ]; then
        echo "Killing existing agent $SSH_AGENT_PID..."
        kill $SSH_AGENT_PID
    fi
    # Run the agent and add the key.
    ssh-agent -s > $sshenv
    . $sshenv
    ssh-add
}

if [ "$(hostname)" == "xxxx" ]; then
    if [ -e $sshenv ]; then
        echo "Restoring ssh-agent environment..."
        . $sshenv
    fi
    # If there is no ssh-agent PID or it's set but not running, restart it.
    if [ -z "$SSH_AGENT_PID" -o ! -e /proc/$SSH_AGENT_PID ]; then
        echo "SSH agent doesn't seem to be running. Restarting..."
        init-ssh-agent
    fi
fi

I'm an idiot. Just use Keychain. http://docs.funtoo.org/wiki/Keychain