#https://android.stackexchange.com/questions/74952/interpretting-the-output-of-dumpsys-telephony-registry
#get Cellular Signal Strength from an android device
while [ 1 ];do adb shell dumpsys telephony.registry | grep -i signalstrength;done

#Narrow it down some for LTE
while [ 1 ];do adb shell dumpsys telephony.registry | grep -i signalstrength|awk '{print $10}';done

#Narrow it down some for GSM
while [ 1 ];do adb shell dumpsys telephony.registry | grep -i signalstrength|awk '{print $2}';done

#Narrow it down some for both
while [ 1 ];do adb shell dumpsys telephony.registry | grep -i signalstrength|awk '{print "GSM:"$2 "  LTE:"$10}';done

#If you haven't set permissions for your user you may need to use 'sudo'
sudo killall adb
sudo adb shell echo test

#more info on output
public String toString() {
    return ("SignalStrength:"
            + " " + mGsmSignalStrength
            + " " + mGsmBitErrorRate
            + " " + mCdmaDbm
            + " " + mCdmaEcio
            + " " + mEvdoDbm
            + " " + mEvdoEcio
            + " " + mEvdoSnr
            + " " + mLteSignalStrength
            + " " + mLteRsrp
            + " " + mLteRsrq
            + " " + mLteRssnr
            + " " + mLteCqi
            + " " + (isGsm ? "gsm|lte" : "cdma"));
}