I have 7 devices plugged into my development machine.
Normally I do adb install and can install to just a single device.
adb install
Now
Here's a functional one line command tailored from kichik's response (thanks!):
adb devices | tail -n +2 | cut -sf 1 | xargs -iX adb -s X install -r *.apk
But if you happen to be using Maven it's even simpler:
mvn android:deploy