persistent ssh keys

.bashrc

SSH_ENV="$HOME/.ssh/environment"
function start_agent {
    echo "Initializing new SSH agent..."
    # spawn ssh-agent
    ssh-agent > "$SSH_ENV"
    chmod 600 "$SSH_ENV"
    . "$SSH_ENV" > /dev/null
}

# check for running ssh-agent with proper $SSH_AGENT_PID
if [[ -r "$SSH_ENV" ]]; then
    . "$SSH_ENV" > /dev/null
    ssh-add -l >/dev/null 2>&1
    if [[ $? == 2 ]]; then
        start_agent
    else
        echo reuse ssh-agent $SSH_AGENT_PID
    fi
else
    start_agent
fi

ssh_config

#~/.ssh/config
Host github.com
    HostName github.com
    User git
    IdentityFile ~/.ssh/my-github