#!/usr/bin/sh

    if df -k | grep '\([7-9][0-9]|[0-9][0-9][0-9]\)%' > /dev/null
    then mailx -s "File system(s) full. Clean up your mess." user@foo.tla <<'--'
    Yada yada yada

    - The angry sysadmin.
    --
    fi