Generate SystemD .network files for network interface automatically

generate-systemd-network.sh

#!/bin/bash -e
# Generate SystemD .network files for network interface automatically
# (c) Pekka Järvinen 2019-

# Check that there are arguments given
if [ "$#" -eq 0 ]; then
    echo "No arguments were given. See $0 --help or $0 -h for usage instructions." 1>&2
    exit 1
fi

generatedwith=$@
beverbose=no
interface=none
dhcp="yes"
address=""
gateway=""
dns=""
match="iface"
priority=10
matchmac=""

# Get current default gateway IP
read _ _ currentgateway _ < <(ip route list match 0/0)

# options may be followed by one colon to indicate they have a required argument
if ! options=$(getopt -o hv:i:a:d:m:g:n:p: -l help,verbose,interface:,address:,dhcp:,match:,gateway:,dns:,priority: -- "$@")
then
    # something went wrong, getopt will put out an error message for us
    exit 1
fi

set -- $options

# Parse arguments
while [ $# -gt 0 ]
do
    case $1 in
    -h|--help)
      echo "Usage: $0"
      echo "  -i --interface <interface>     Required. for example: eno1"
      echo "  -p --priority 0-n              Priority. Defaults to 10. "
      echo ""
      echo "Match type (defaults to iface):"
      echo "  -m --match <iface|mac>    [Match] definition for example: iface for Name="
      echo ""
      echo "Use DHCP (default: yes):"
      echo "  -d --dhcp <no|yes|ipv4|ipv6>    For example: ipv4"
      echo ""
      echo "Use static IP address:"
      echo "  -a --address <IPv4|IPv6 with CIDR>   For example: 192.168.1.19/24"
      echo "  -g --gateway <Gateway IP Address>    Defaults to current GW. For example: 192.168.1.1"
      echo "  -n --dns <DNS IP Address>            For example: 192.168.1.1"
      echo ""
      echo "Other:"
      echo "  -v --verbose be verbose"
      echo "  -h --help this help"
      echo ""
      echo "Examples:"
      echo "  Use static IP:"
      echo "    $0 -i eno1 -d no -a 192.168.1.10/24 --gateway 192.168.1.1 --dns 192.168.1.1"
      echo "  DHCP IPv4:"
      echo "    $0 -i eno1 -d ipv4"
      echo ""
      exit 0
    ;;

    -v|--verbose) beverbose="yes" ;;
    -f|--force) force="yes" ;;

    # for options with required arguments, an additional shift is required
    -i|--interface) interface="${2//\'/}" ; shift;;
    -a|--address) address="${2//\'/}" ; shift;;
    -d|--dhcp) dhcp="${2//\'/}" ; shift;;
    -m|--match) match="${2//\'/}" ; shift;;
    -g|--gateway) gateway="${2//\'/}" ; shift;;
    -n|--dns) dns="${2//\'/}" ; shift;;
    -p|--priority) priority="${2//\'/}" ; shift;;
  

    (--) shift; break;;
    (-*) echo "$0: error - unrecognized option $1" 1>&2; exit 1;;
    (*) break;;
    esac
    shift
done

# Check arguments for conflicts and errors

macfile=/sys/class/net/$interface/address

if [ -f "$macfile" ]; then
  # Get MAC Address of given interface
  matchmac=$(< $macfile)
else
  echo "Unknown interface: $interface ($macfile)" 1>&2
  exit 1
fi

case $dhcp in
  yes|no|ipv6|ipv4) ;;
  *) echo "Unknown DHCP type: $dhcp. Use yes|no|ipv6|ipv4" 1>&2; exit 1;;
esac

if [ "$dhcp" != "no" -a "$address" != "" ]; then
  echo "Can't mix DHCP and static IP config" 1>&2
  exit 1
fi

if [ "$address" != "" -a ! -z "${address##*/*}" ]; then
  echo "No CIDR in static IP $address. Use for example 'IP/24' which is 255.255.255.0." 1>&2
  exit 1
fi

case $match in
  mac|iface) ;;
  *) echo "Unknown match type: $match. Use mac|iface." 1>&2; exit 1;;
esac


# Output the .network file contents to temporary file

ofn=$priority-$interface.network
ofile=$(mktemp -d "${TMPDIR:-/tmp/}$(basename $0).XXXXXXXXXXXX")/$ofn

echo "# sudo cp -i $ofile /etc/systemd/network/$ofn" > $ofile
echo "# -- Generated with $0 $generatedwith" >> $ofile
echo -n "# -- At " >> $ofile
date --iso-8601=seconds >> $ofile
echo "#" >> $ofile

# Match
echo "[Match]" >> $ofile
echo "# Match MAC Address" >> $ofile
if [ "$match" != "mac" ]; then
  echo -n "#" >> $ofile
fi
echo "MACAddress=$matchmac" >> $ofile

echo "# Match name" >> $ofile
if [ "$match" != "iface" ]; then
  echo -n "#" >> $ofile
fi 
echo "Name=${interface}" >> $ofile
echo "" >> $ofile

# Network
echo "[Network]" >> $ofile
echo "Description=Interface $interface (network)" >> $ofile

echo "# DHCP no|yes|ipv4|ipv6" >> $ofile
if [ "$dhcp" == "no" ]; then
  echo -n "#" >> $ofile
fi
echo "DHCP=$dhcp" >> $ofile

echo "# Static IPv4 or IPv6 address with CIDR" >> $ofile
if [ "$dhcp" != "no" ]; then
  echo -n "#" >> $ofile
fi
echo "Address=$address" >> $ofile

echo "# Generated automatically from current configuration:" >> $ofile
for addr in $(ip address show dev $interface | awk '/inet/{print $2}')
do
  echo "#Address=$addr" >> $ofile
done

echo "# Gateway IP Address" >> $ofile

if [ "$gateway" == "" ]; then
  gateway=$currentgateway
fi

if [ "$dhcp" != "no" ]; then
  echo -n "#" >> $ofile
fi
echo "Gateway=$gateway" >> $ofile

echo "# DNS server address" >> $ofile

if [ "$dns" == "" ]; then
  dns=$gateway
  echo -n "#" >> $ofile
fi
echo "DNS=$dns" >> $ofile

echo "#Domains=home.lan" >> $ofile
echo "#DNSDefaultRoute=" >> $ofile
echo "# NTP time keeping server" >> $ofile
echo "#NTP=$gateway" >> $ofile
echo "# Forward packets (req for NAT)" >> $ofile
echo "#IPForward=no" >> $ofile
echo "#IPMasquerade=" >> $ofile
echo "# VLAN ID" >> $ofile
echo "#VLAN=1234" >> $ofile
echo "#LinkLocalAddressing=no" >> $ofile
echo "#LLMNR=no" >> $ofile
echo "#LLDP=" >> $ofile
echo "# Send LLDP packets" >> $ofile
echo "EmitLLDP=nearest-bridge" >> $ofile
echo "" >> $ofile

# Link

echo "[Link]" >> $ofile
echo "# Override MAC (spoof)" >> $ofile
echo "#MACAddress=" >> $ofile
echo "#ARP=no" >> $ofile
echo "#Multicast=no" >> $ofile
echo "#Unmanaged=no" >> $ofile
echo "#RequiredForOnline=yes" >> $ofile
echo ""

cat $ofile