#!/bin/bash
s='//INALL TYPE=GH,WORK=HU.ET.ET(IO)
//INA2 WORK=HU.TY.TY(OP),TYPE=KK
//OOPE2 TYPE=KO,WORK=TEXT.LO1.LO2,TEXT
//OOP2 TYPE=KO,WORK=TEST1.TEST2
//H1 WORK=OP.TEE.GHU,TYPE=IU'
sed -n '/WORK=.*([^()]*)/!s/.*WORK=\([^,]*\).*/\1/p' <<< "$s"
IyEvYmluL2Jhc2gKcz0nLy9JTkFMTCBUWVBFPUdILFdPUks9SFUuRVQuRVQoSU8pCi8vSU5BMiBXT1JLPUhVLlRZLlRZKE9QKSxUWVBFPUtLCi8vT09QRTIgVFlQRT1LTyxXT1JLPVRFWFQuTE8xLkxPMixURVhUCi8vT09QMiBUWVBFPUtPLFdPUks9VEVTVDEuVEVTVDIKLy9IMSBXT1JLPU9QLlRFRS5HSFUsVFlQRT1JVScKc2VkIC1uICcvV09SSz0uKihbXigpXSopLyFzLy4qV09SSz1cKFteLF0qXCkuKi9cMS9wJyA8PDwgIiRzIg==