If you already have code written for your Arduino yun which uses the Yun bridge and you want to run it on your Linkit 7688 Duo you can also enable this library.
Use following commands to enable Bridge library on LinkIt Smart 7688 Duo:
uci set yunbridge.config.disabled='0' uci commit reboot
In your sketch you can now add Bridge.begin(); in the setup which will trigger the run-bridge shell script which invokes python bridge.py from /usr/lib/python2.7/bridge.