Thanks for your reply.
Actually, I was trying to write a script which enables normal users to change their route. I wrote a bash script & set SUID, thinking that that script will run with root privilege & users can change their route using following commands.
route del default
route add default gw 192.168.0.5
But even though SUID is set, the users get permission denied error. However I managed to solve this problem by calling this bash script from a C compiled program.
setuid( 0 );
system( "/path/to/bash-script" );
# chmod u+s call-script
Now users can execute ./call-script & can chanage their route with root privilege.
So , I assume that setuid bit is disabled on shell scripts(bash) & can be used only with binary executable. Please correct me If I am wrong ....