#!/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"