source: vendor/bash/3.1/examples/functions/isvalidip

# Thanks to Chris F. A. Johnson <c.f.a.johnson@rogers.com> for this one
is_validip()
{
        case "$*" in
        ""|*[!0-9.]*|*[!0-9]) return 1 ;;
        esac

        local IFS=.
        set -- $*

        [ $# -eq 4 ] &&
            [ ${1:-666} -le 255 ] && [ ${2:-666} -le 255 ] &&
            [ ${3:-666} -le 255 ] && [ ${4:-666} -le 254 ]
}