UNIX for Dummies Questions & Answers

while [ $answer != X || $answer != x ]

while [ "$answer" != "x" ] || [ "$answer" != "X" ]

answer=x
while [ $answer != X && $answer != x ]
do
echo "Phone Book"
echo "Phone Company"
echo "Company Number"
echo ""
echo ""
echo "A - Add a new line in the phone book"
echo "D - Delete a line from the phone book"
echo "M - Modify a line in the phone book"
echo "I - Inquire on a name in the phone book"
echo "X - Exit"
echo ""
echo ""
echo "What would you like to do? \c"
read answer
case $answer in