RedHat/CentosOS version 4 or 5 check in bash

grep -i 'release 4' /etc/redhat-release > /dev/null && DISTRO=RHEL4
grep -i 'release 5' /etc/redhat-release > /dev/null && DISTRO=RHEL5


case $DISTRO in
        RHEL4)
             echo "verison 4"
                ;;
        RHEL5)
                echo "version 5"
                ;;
        *)
                echo "this is no CentOS4/CentOS5 or RedHat4/RedHat5"
                exit 
                ;;
esac