nixos/acpid: pass event parameters to handler (#34190)

Previously the parameters were just dropped. Now they can be read
from within the handler script. An example to show this is added.

Makes use of the new writeShellScript function as suggested in:
issue #21557

resolves:  #21557

nixos/modules/services/hardware/acpid.nix

@@ -31,7 +31,7 @@ let
           ''
             fn=$out/${name}
             echo "event=${handler.event}" > $fn
-            echo "action=${pkgs.writeScript "${name}.sh" (concatStringsSep "\n" [ "#! ${pkgs.bash}/bin/sh" handler.action ])}" >> $fn
+            echo "action=${pkgs.writeShellScriptBin "${name}.sh" handler.action }/bin/${name}.sh '%e'" >> $fn
           '';
         in concatStringsSep "\n" (mapAttrsToList f (canonicalHandlers // config.services.acpid.handlers))
       }
@@ -69,11 +69,33 @@ in
           };
         });
 
-        description = "Event handlers.";
+        description = ''
+          Event handlers.
+
+          <note><para>
+            Handler can be a single command.
+          </para></note>
+        '';
         default = {};
-        example = { mute = { event = "button/mute.*"; action = "amixer set Master toggle"; }; };
-
-
+        example = {
+          ac-power = {
+            event = "ac_adapter/*";
+            action = ''
+              vals=($1)  # space separated string to array of multiple values
+              case ''${vals[3]} in
+                  00000000)
+                      echo unplugged >> /tmp/acpi.log
+                      ;;
+                  00000001)
+                      echo plugged in >> /tmp/acpi.log
+                      ;;
+                  *)
+                      echo unknown >> /tmp/acpi.log
+                      ;;
+              esac
+            '';
+          };
+        };
       };
 
       powerEventCommands = mkOption {