I know what's the problem now. I have another question.
Code:
#!/bin/ksh
#
OPT1='zenity --entry --text="Please input the host IP:" --title "input IP address:'
The code above does not prompt the zenity window as I put the input ip address value to OPT1. How do I make it prompt the window while save the input value to OPT1 ?
Problem solved. I substitute OPT1=$()