Hi
I have tried to disable the CTRL-Z key inside a shell(sh) script using the command trap "`echo "Ctrl-Z key disabled"`" 20But I am not able to exit from the script after pressing CTRL-Z key.
How to proceed this? Need reply soon

See Vino's suggestion below (sorry, I was in a rush and in the middle of this and real work)

Wouldn't this be better off ?

trap "echo "Ctrl-Z key disabled" SIGTSTP

SIGTSTP 	24 	Stop 	Stop (job control, e.g., ^z))

$ kill -l SIGTSTP
20
$ kill -l 20
TSTP
$ kill -l TSTP
20
$ kill -l 24
XCPU

Tried the following on Solaris (2.6 and 8)

#!/bin/ksh
trap "" SIGTSTP
echo "try it - should not work"
sleep 15
trap - SIGTSTP
exit

Tried this on linux and it worked.

#!/bin/ksh

trap "" TSTP
echo "try it - should not work"
sleep 15
trap - TSTP
exit

./rtm.ksh[3]: trap: bad signal SIGTSTP

$ ./rtm.ksh  
try it - should not work
[1] + Stopped              ./rtm.ksh 
$ fg
./rtm.ksh

TSTP worked on solaris.

Signals in a shell script become very complex very fast. Notice that the OP complained about using:
trap "`echo "Ctrl-Z key disabled"`" 20
Using the correct quoting is not any better:
trap "echo Cntl-Z key disabled" 20

You guys are proposing:
trap "" 20
which works fine. Whole different stretch of road. Try your scripts using the above trap statement. When you get tried of waiting for them, open another window, locate that sleep process, and do a "kill -CONT" to it.

Control Z is usually the SUSP character. Typing the SUSP characters sends SIGTSTP to all processes in the terminal's foreground process group. To disable control Z, the command is:
stty susp ^-
All of the posts here deal with catching or ignoring the TSTP signal, not disabling Control Z. Remember that shell scripts are collections of processes. The shell uses fork() and exec () to run the sleep program. From the exec man page: So when TSTP is ignored, it stays ignored during the execution of the sleep process. But if it was caugth, it goes back to the default action which is to suspend the process. This is bad enough, but what's more, ksh has some bug involving caught job control signals. ksh has it own internal routine to catch those signals. It gets run instead of the specified command. So you don't even get the the message echoed.

I can only curse the darkness. I don't have a candle to light. Sorry.