ShellPresenceSensor invert state

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Hi,

When executing a shell command the command usually returns 0 on success, and something else on failure. The return value of a command can be displayed using echo $?. So, to make the return value compatible for the ShellPresenceSensor the 0 has to be transformed to a 1 and other return values should be transformed to a 0. I do this in the following way:
if <some command>; then echo 1; else echo 0; fi

I think it would be nice to have an invert option in the ShellPresenceSensor which inverts the state of the command. That way the following could be used:
<some command>; echo $?

Or maybe it is possible if the return value of the command is handled directly by the ShellPresenceSensor where a return value of 0 is interpreted as present and any other return value as not present.

I think the same could apply to the getStateCommand of the ShellSwitch

Also I think it would be good if true/false and on/off values would be validated case insensitive.

Tip of the day: Rather than writing if <some command>; then echo 1; else echo 0; fi you can simply write ! <some command>; echo $?. That’s the beauty of POSIX shell since 1991

Thanks @mwittig, I use Unix for a long time and wasn’t aware of this. One still has to echo $?, perhaps the ShellPresenceSensor and ShellSwitch could handle the return value directly

@rrooggiieerr said in ShellPresenceSensor invert state:

One still has to echo $?,

Yes. The “not” operator just inverts the exit code. You still need to output the exit code on stdout as the shell device will read the state from output generated by spawned process.

perhaps the ShellPresenceSensor and ShellSwitch could handle the return value directly

Possibly as an option, however, not for all use cases. For example, a common use case is to use the curl command to query some device state and to parse the state (e.g. ON/OFF, present/absent) from the response received by the curl command. See https://forum.pimatic.org/topic/1842/pimatic-shell-switch-general-problem or https://forum.pimatic.org/topic/979/denon-marantz-avr-remote-control which use this pattern