shell script for replace, add, and delete

#! /bin/sh

echo "what you want to do"
echo "1:user change department"
echo "2:user change PC"
echo "3:add PC"
echo "4.delete PC"
read ANSWER

if [ $ANSWER = "1" ]; then
        echo "Enter User name"
        read USER1
        echo "Enter PC number"
        read PC1
        echo "Enter previous department name"
        read OLD1
        echo "Enter new department name"
        read NEW1

        sed -i '/'"$PC1"'/d' $OLD1
        echo "172.30.10."$PC1"  #"$USER1 >> $NEW1
        echo "Success"



elif [ $ANSWER = "2" ]; then
        echo "Enter previous PC number"
        read PC2
        echo "Enter new PC number"
        read NEW2
        echo "Enter department name"
        read DEPARTMENT2

        sed 's/'"$PC2"'/'"$NEW2"'/' $DEPARTMENT2 > $DEPARTMENT2".temp"
        cat $DEPARTMENT2".temp" > $DEPARTMENT2
        rm -rf $DEPARTMENT2".temp"

elif [ $ANSWER = "3" ]; then
        echo "Enter user name"
        read USER
        echo "Enter PC number"
        read PC3
        echo "Enter department name"
        read DEPARTMENT3

        echo "172.30.10."$PC3"  #"$USER >> $DEPARTMENT3

elif [ $ANSWER = "4" ]; then
        echo "Enter PC number"
        read PC4
        echo "Enter department name"
        read DEPARTMENT4

        sed -i '/'"$PC4"'/d' $DEPARTMENT4


else
        echo "you had enter an invalid number"

fi