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

#
# inet2hex - Internet address conversion, dotted-decimal to hex
#
inet2hex ()
{
        local IFS

        IFS=.
        set -- $1

        if (( $# != 4 )); then
                echo "inet2hex: incorrect input format: $1" >&2
                echo "inet2hex: usage: inet2hex XX.XX.XX.XX" >&2
                return 2
        fi
  
        printf "0x%02x%02x%02x%02x\n" $1 $2 $3 $4
}

#
# hex2inet - Internet address conversion, hex to dotted-decimal
#
hex2inet ()
{
        local x1 x2 x3 x4
        local rev

        OPTIND=1
        while getopts "r" o
        do
                case "$o" in
                r)      rev=true;;
                *)      echo "hex2inet: usage: hex2inet [-r] [0x]XXXXXXXX" >&2 ; exit 2;;
                esac
        done
        shift $(( $OPTIND - 1 ))

        case "$1" in
        0x*)    h=${1#??} ;;
        *)      h=$1 ;;
        esac

        if (( ${#h} != 8 )); then
                echo "hex2inet: $h not in inet format" >&2
                echo "hex2inet: usage: hex2inet [0x]XXXXXXXX" >&2
                return 2
        fi

        x1=$(( 0x${h:0:2} ))
        x2=$(( 0x${h:2:2} ))
        x3=$(( 0x${h:4:2} ))
        x4=$(( 0x${h:6:2} ))

        if [ -z "$rev" ] ; then
                printf "%d.%d.%d.%d\n" $x1 $x2 $x3 $x4 
        else
                printf "%d.%d.%d.%d\n" $x4 $x3 $x2 $x1 
        fi
        return 0
}