Start ssh-agent on login

.zshenv

SSH_ENV="$HOME/.ssh/environment"

function start_agent {
    /usr/bin/ssh-agent | sed 's/^echo/#echo/' > "${SSH_ENV}"
    chmod 600 "${SSH_ENV}"
    . "${SSH_ENV}" > /dev/null
    /usr/bin/ssh-add 2> /dev/null;
}

if [ -z "$SSH_AUTH_SOCK" ]; then
    # Source SSH settings, if applicable
    if [ -f "${SSH_ENV}" ]; then
        . "${SSH_ENV}" > /dev/null
        ps -ef | grep ${SSH_AGENT_PID} | grep ssh-agent$ > /dev/null || {
            start_agent;
        }
    else
        start_agent;
    fi
fi