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Re: units_cur

From: Pierre Neidhardt
Subject: Re: units_cur
Date: Sun, 01 Apr 2018 18:36:05 +0530
User-agent: mu4e 1.0; emacs 25.3.1

I want to update whenever the file is older than 1 day (so that it does
not do anything on reboot for instance) and every 1 day
from then on (so that it keeps updating even if I don't reboot).

For that I need mcron with some condition on the mtime of

Here is my implementation:

        ;; -*- mode: Lisp; -*-

        ;; This cannot be let-bound within `job'.
        (define currency-file (string-append (getenv "HOME") 

         (lambda (current-time)
           (let* ((seconds-in-a-day (* 60 60 24))
                  (currency-time (stat:mtime (stat currency-file))))
             (if (< currency-time (- current-time seconds-in-a-day))
               ;; TODO: The following does not work while it should.  Report 
               ;; (next-hour-from (next-day) (list (tm:hour (localtime 
               (+ (next-second) (- 86400 (- current-time currency-time))))))
         ;; A string is nicer than Scheme code for `mcron --schedule' output.
         ;; Other we could return '(system* "units_cur" currency-file)
         (string-append "units_cur " currency-file))

I start ~mcron~ from my ~.profile~:

        mcron &

Comments are welcome :)

Note: As mentioned in the "TODO:" above, I think there is a bug in
mcron.  The following example taken from the Guix manual does not seem
to work:

     (define idutils-job
       ;; Update the index database as user "charlie" at 12:15PM
       ;; and 19:15PM.  This runs from the user's home directory.
       #~(job '(next-minute-from (next-hour '(12 19)) '(15))
              (string-append #$idutils "/bin/mkid src")
              #:user "charlie"))

Or, at the user level:

        (job '(next-minute-from (next-hour '(12 19)) '(15))
              (string-append (getenv "HOME") "/.guix-profile/bin/mkid src"))

        > mcron -s 1
        mcron: Cannot read files in your ~/.config/cron (or ~/.cron) directory.

More specifically, it seems that mcron fails to take a list as second
argument to the ~next-*~ functions.

Can anyone confirm?

Pierre Neidhardt

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