One option is to temporarily close standard input, then the ksh has nothing to read from:

Code:

script_b.sh
=========
exec <&-
./script_A.sh
exec < /dev/tty
echo "I am in script B"
 
 
# ./Script_B.sh 
In am in script A
I am in script B

otherwise, something like:

Code:

script_b.sh
=========
echo | ./script_A.sh
echo "I am in script B"
 
 
# ./Script_B.sh 
In am in script A
I am in script B

While these work for the example you've shown, I'm guessing they might have a bad effect on script_a.sh (especially the first) - so not really a solution.

If you type "exit" when you get to this point:

Code:

$> Script_B.sh
$> I am in script A
$>

then script_b.sh will continue:

Code:

# ./Script_B.sh 
In am in script A
# exit
I am in script B

Also not ideal.

I would find whoever wrote script_a and ask him what he was thinking! Or better, why not copy script_a to script_c, remove the ksh and call that from script_b?