I've tried this, however TWRP seems to not be executing the openrecoveryscript file.
I modified the Task to be one line "Run Shell"
chmod 0777 /cache/recovery
echo "backup SDCRBM weeklybackup" > /cache/recovery/openrecoveryscript
echo "reboot" >> /cache/recovery/openrecoveryscript
chmod 777 /cache/recovery/openrecoveryscript
I even added the chmod 777 to make sure that I'm not running into permission problems when TWRP tries to use the file.
I verified that tasker is writing to /cache/recovery by running in Termux:
backup SDCRBM weeklybackup
I'm at a loss. I feel like I'm missing one silly little detail. Any help would be appreciated.
LineageOS 16.0 unofficial / TWRP 3.2.3 on Samsung Galaxy S7