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-rw-r--r--doc/guix.texi34
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.