Set up Linux to use an ssh-agent at login

ssh-agent-start.sh

## References
# http://www.cygwin.com/ml/cygwin/2001-06/msg00537.html
# https://help.github.com/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent/


# I've modified the script in the first to work with the MacOS-specific info in
# the second. The procedure below should get you what you need, though.


# Postreq: Add the below (or a reference to it) to .profile or similar.

# ssh-agent: Where we're tracking the ssh-agent settings
SSH_ENV="$HOME/.ssh/environment"

# ssh-agent: Start the agent and track the settings
function start_ssh_agent {
     echo -n "Initialising new SSH agent: "
     /usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}"
     echo "Done"
     chmod 600 "${SSH_ENV}"
     . "${SSH_ENV}" > /dev/null
     /usr/bin/ssh-add;
}

# ssh-agent: Check that the agent is running; If not, start it.
function ensure_ssh_agent {
    if [ -f "${SSH_ENV}" ]; then
        . "${SSH_ENV}" > /dev/null
        ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
            start_ssh_agent;
        }
    else
        start_ssh_agent;
    fi
}

# ssh-agent: kickoff
ensure_ssh_agent