You can do this by using adb command line tools OR gradle commands: See this Guide.
Setup command line adb
export PATH=/Users/mayurik/Library/Android/sdk/platform-tools/adb:/Users/mayurik/Library/Android/sdk/tool
Gradle commands to build and install.
#Start Build Process
echo "\n\n\nStarting"
./gradlew clean
./gradlew build
./gradlew assembleDebug
#Install APK on device / emulator
echo "installDebug...\n"
./gradlew installDebug
You can also uninstall any previous versions using
`./gradlew uninstallDebug`
You can launch your main activity on device/emulator like below
#Launch Main Activity
adb shell am start -n "com.sample.androidbuildautomationsample/com.sample.androidbuildautomationsample.MainActivity" -a android.intent.action.MAIN -c android.intent.category.LAUNCHER