Hi
I am trying to write a code like this
echo "enter a type"
read a_type
while [ $a_type != "S" ] || [ "$a_type" != "s" ] || [ "$a_type" != "SR" ] || [ "$a_type" != "sr" ] || [ "$a_type" != "a" ] || [ "$a_type" != "A" ]
do
echo "invalid engine type Please enter correct a_type"
read engine_type < /dev/tty
done

My problem is that even if i give the a_type as the correct one that i have listed above that is S or s so on and so forth it is still entering in the loop and telling invalid a_type
Instead if i give = condition in while it is working fine . That is if i give while [ $a_type = "S" ] then if i give S it is entering and not S it is not entering . But giving = dosent satisfy my code . I have to give not equal to if i want the code to work
Please help
Thanking in advance