Control Hubs: Bringing It All Together - Smart Home Automation with Linux and Raspberry Pi - page 264

Using the cdplayer example again, the remote machine processes a command that now looks like this, if it were
to be processed locally:

cdplayer localhost play 1

Bearskin Compatibility
To make your own commands compatible with Marple, you need to begin your scripts with a few extra lines of code.
Here's an example:

DEVICE=`$MINBIN/finddev mixer $*´
if [ $? == 0 ]; then
echo $DEVICE
exit 0;
fi

This rather strange-looking piece of code makes use of both the finddev output and its exit code. It returns a 0 in
those cases where the device name was found but wasn't intended for this machine. In other words, it has dispatched
a SOAP request or similar and 1 when a genuine device was found. The latter is more usual and ends up being
/dev/dsp or similar. As far as the command scripts go, this is all that's necessary.
The extra work comes from creating a local devlist . But each is generally a carbon copy of the others. Namely,
a file called $MINBASE/etc/devices/new_app_name/devlist should be created and appear like this, replacing /dev/dvd
with a suitable device for your app:

localhost dev /dev/dvd - -
default dev /dev/dvd - -

Note that the local devlist file should always include a default and localhost reference. This ensures that
every query can terminate and stops recursive loops from happening.

N Some low-level software, such as the CD player program cdcd , requires $HOME to be set up before the program
can be run. This requires the machine charged with processing SOAP requests to add this extra line of code
and sometimes prepare a .cdcdrc file in the home directory of the www-data user.

Note

Utility Scripts
A quick perusal of the $MINBASE/bin directory will reveal a number of commands that haven't yet been covered.
These divide into status and user tools.

Status
These are the simplest to consider and are basic scripts that perform read-only tasks to report on the various
elements of the system. Because of the architecture, this is usually nothing more complex than reading text files in
the /var/log/minerva directory or querying the existing commands.