How to capture pid of (system process?

[Jacob Hrbek <kreyren@rixotstudio.cz>]

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I wrote this potato-make <https://github.com/spk121/potato-make> 
definition (was simplified):

#:SRC_BEGIN sheme-mode
#!/usr/bin/env sh
exec guile -s "$0" "$@"
!#

(use-modules (ice-9 futures)
  (potato make))
(initialize)

(: "watch" '()
    (~ (do ((i 1 (1+ i)))
       ((> i 6))
     (future (system
      "emacs"))
     ;;(let ((emacs_pid (getpid)))
      ;; (kill emacs_pid SIGTERM)))))

(execute)
#:SRC_END

expecting to capture emacs's pid and kill it, but the issue is that 
using `getpid` gets me the PID of potato-make and `getppid` of the shell 
-> How can i capture just the emacs's pid?

FWIW the projected end-goal is 3600 loop that checks if the 
`my-theme.el` file has been changed to re-launch emacs with the theme 
loaded used for theme development.


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