if [[ -z $MAIL ]] {
    if [[ $OSTYPE = (ultrix4|osf)* ]] {
       export MAIL=/usr/spool/mail/$USER 
    } elif [[ $OSTYPE = hpux9* ]] {
       export MAIL=/usr/mail/$USER 
    } elif [[ $OSTYPE = solaris2* ]] {
       export MAIL=/var/mail/$USER 
    } elif [[ $OSTYPE = sunos4* ]] {
       export MAIL=/usr/spool/mail/$USER 
    } else {
       echo 'WARNING: $MAIL' "not set for $OSTYPE."
    }
}