I think you have to have the openhab exec binding installed for executeCommandLine to work. If you installed openhab with apt-get, then you should install the binding with apt-get too:
sudo apt-get install openhab-addon-binding-exec
If you didn’t use apt-get to install openhab, you can probably just copy this addon to your addons directory:
org.openhab.persistence.exec-1.8.3.jar
or whatever version of openhab you’re using.
You can see this post for other suggestions on making executeCommandLine work:
https://community.openhab.org/t/solved-exec-binding-does-nothing-on-executecommandline/8778/10