$name battd
$source https://the-tk.com/cgit/battd/

battd is a simple battery daemon written for use with a daemontools-style
supervisor.

$desc

The daemon `run` script polls the status of a user defined `check` function
every `long_interval` or `short_interval` seconds. The interval is determined by
the status of the `interval` function. On the transition from a successful
`check` exit status to an unsuccessful `check` exit status the `failed` function
is called. These functions and optionally the variables `long_interval` and
`short_interval` need to be provided in a `conf` file located in the same
directory as the script.

The following `conf` file contains an example configuration which increases the
polling interval from 5 minutes to 30 seconds when the battery level is below 16
percent or fewer than 20 minutes of battery life remain and puts the machine in
a hybrid sleep once the battery level is below 8 percent or fewer than 10
minutes of battery life remain.

```sh
battery=/sys/class/power_supply/BAT0/uevent
interval() { ./battcheck min_time=1200 min_pct=16 "$battery"; }
check() { ./battcheck min_time=600 min_pct=8 "$battery"; }
failed() { zzz -H; }
```

Finally, the `battcheck` awk script takes two optional command line variable
assignments for `min_pct` and `min_time` specifying the remaining battery
percentage and remaining battery time in seconds respectively after which the
script will produce an unsuccessful exit code.

These files should be placed inside a service directory making sure that `run`
and `battcheck` are both executable. The service handles SIGHUP to reload its
configuration at runtime.

The `battcheck` script is quite versatile and may be useful in other contexts, in
which case it is recommended to install it to `/usr/local/sbin` or another
appropriate location.

If the script crashes before a success to failure transition of the `check`
function and is re-started after the transition then the script will incorrectly
ignore this transition and not call the `failed` function. This could be fixed
by storing the previous status in on a temporary file system but this was not
done due to the unlikelihood of the event and in order to keep the code simple.