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| -rw-r--r-- | doc/guix.texi | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/doc/guix.texi b/doc/guix.texi index 043851e418..8f2608d5af 100644 --- a/doc/guix.texi +++ b/doc/guix.texi @@ -12442,6 +12442,40 @@ gexps to introduce job definitions that are passed to mcron %base-services))) @end lisp +For more complex jobs defined in Scheme where you need control over the top +level, for instance to introduce a @code{use-modules} form that defines syntax +(macros), you can move your code to a separate program using the +@code{program-file} procedure of the @code{(guix gexp)} module +(@pxref{G-Expressions}). The example below illustrates that. + +@lisp +(define %battery-alert-job + ;; Beep when the battery percentage falls below %MIN-LEVEL. + #~(job + '(next-minute (range 0 60 1)) + #$(program-file + "battery-alert.scm" + (with-imported-modules (source-module-closure + '((guix build utils))) + #~(begin + (define %min-level 20) + (use-modules (guix build utils) + (ice-9 popen) + (ice-9 regex) + (ice-9 textual-ports) + (srfi srfi-2)) + (setenv "LC_ALL" "C") ;ensure English output + (and-let* ((input-pipe (open-pipe* + OPEN_READ + #$(file-append acpi "/bin/acpi"))) + (output (get-string-all input-pipe)) + (m (string-match "Discharging, ([0-9]+)%" output)) + (level (string->number (match:substring m 1))) + ((< level %min-level))) + (format #t "warning: Battery level is low (~a%)~%" level) + (invoke #$(file-append beep "/bin/beep") "-r5"))))))) +@end lisp + @xref{Guile Syntax, mcron job specifications,, mcron, GNU@tie{}mcron}, for more information on mcron job specifications. Below is the reference of the mcron service. |