I'm using start-process to run a process upon certain events picked up with hooks

(start-process "foo" "*Foo*" foo-command foo-args)

I would like to do 2 things with this.

  • Prevent the process from being started if it's already running
  • Print a message to *Messages* when the process is complete

How can I do this please?

  • Please do not post the same question here and to StackOverflow. Choose one. Please delete one of these posts. Thx. – Drew Jun 3 '17 at 21:40
  • 2
    Have a look at set-process-sentinel to designate a function that generates a message when finished. See also get-process and related functions: gnu.org/software/emacs/manual/html_node/elisp/… This thread has a few examples: stackoverflow.com/questions/24548536/… Google set-process-sentinel, start-process, process-filter for additional examples. – lawlist Jun 3 '17 at 21:41
  • @lawlist perhaps you could convert that to an answer, because process sentinels are the correct approach, and there isn't currently an Answer which explains that. – phils Nov 1 '17 at 9:59

To see if a named process is currently running, you could use the process-status function. It will return nil if the named process is not running ...

process-status is a built-in function in `C source code'.

(process-status PROCESS)

Return the status of PROCESS.
The returned value is one of the following symbols:
run  -- for a process that is running.
stop -- for a process stopped but continuable.
exit -- for a process that has exited.
signal -- for a process that has got a fatal signal.
open -- for a network stream connection that is open.
listen -- for a network stream server that is listening.
closed -- for a network stream connection that is closed.
connect -- when waiting for a non-blocking connection to complete.
failed -- when a non-blocking connection has failed.
nil -- if arg is a process name and no such process exists.
PROCESS may be a process, a buffer, the name of a process, or
nil, indicating the current buffer's process.

And as stated here, a process sentinel is a way for code to be invoked (such as displaying a message) when the process ends.


For your first question, you could iterate over the process-list and only run your command if the process is not found, eg.

(defun process-running-p (name)
  (cl-loop for proc in (process-list)
     if (and (string= name (process-name proc))
             (process-live-p proc))
     return t))

;; ignore if running and live
(unless (process-running-p "foo")
  • See also the following related example that deals with similar process names due to subsequent calls before a prior process has finished; e.g., preview; preview<1>; preview<2>; etc. stackoverflow.com/a/20023781/2112489 – lawlist Jun 3 '17 at 22:04

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