(defmacro with-ssh-agent
  "Bind an ssh-agent for use as identity manager.
The argument vector can be empty, in which case a new agent is created.  If passed a String or File, then this is passed to the new agent as an identity to be added.
An existing agent instance can alternatively be passed."
  [[& agent] & body]
  `(binding [*ssh-agent*
             ~(if (seq agent)
                `(let [arg# ~(first agent)]
                   (if (ssh-agent? arg#)
                     arg#
                     (create-ssh-agent ~@agent)))
                `(create-ssh-agent))]
     ~@body))