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
This command works perfect adb devices | awk 'NR>1{print $1}' | xargs -n1 -I% adb -s % install foo.apk
adb devices | awk 'NR>1{print $1}' | xargs -n1 -I% adb -s % install foo.apk