4-agent

# shellcheck shell=ksh
# vim: syntax=sh et ts=2 sw=2 sts=2

start_ssh_agent ()
{
  # Bail out early if the ssh directory
  # is not found.
  if [ ! -d ~/.ssh ]; then
    return
  fi
  # Determine whether we are inside of an
  # interactive shell and that ssh-agent
  # is actually installed on the host.
  if [[ $(command -v ssh-agent) ]] && \
      [[ $- = *i* ]]; then
    auth_socket=~/.ssh/agent.$(hostname -s).sock
    # If we do not have an active ssh-agent
    # socket, create one and start up a new
    # agent pointing towards it.
    if [[ ! -S $auth_socket ]]; then
      # Remove the socket should an error occur,
      # preventing future agents from connecting
      # to the in-use socket bind address.
      if ! eval "$(ssh-agent -a "$auth_socket" -t 28800)" >/dev/null 2>&1; then
        rm -f "$auth_socket"
      fi
    # Otherwise, check for an already running
    # ssh-agent and similarly point at the
    # existing socket.
    elif [[ -n $(pgrep ssh-agent) ]]; then
      export SSH_AUTH_SOCK=$auth_socket
    fi
    unset auth_socket
  fi
}; start_ssh_agent
unset -f start_ssh_agent