connect (and reconnect) to an lte(mbim) connection and set the network using systemd-networkd

mm-connect.sh

#!/bin/sh

MODEM="$(mmcli -L | grep -o '/org/freedesktop/ModemManager1/Modem/[0-9]*' | head -1)"
BEARER="$(mmcli -m $MODEM --list-bearers | grep -o '/org/freedesktop/ModemManager1/Bearer/[0-9]*' | head -1)"

connect() {
  MODEM="$(mmcli -L | grep -o '/org/freedesktop/ModemManager1/Modem/[0-9]*' | head -1)"

  mmcli -m $MODEM --simple-connect=apn=web.be,user=web,password=web
  BEARER="$(mmcli -m $MODEM --list-bearers | grep -o '/org/freedesktop/ModemManager1/Bearer/[0-9]*' | head -1)"
}

update_net() {
  export connected="no"
  eval export a=a $(mmcli -m $MODEM -b $BEARER | sed -n 's_.*|\s*\([a-zA-Z]*\):\s*\(.*\)_\1="\2"_p' | tr -d "',")
  
  if [ "$connected" != "yes" ]
  then
    echo Reconnecting
    connect
    return 1
  fi

  cat > /run/systemd/network/wwan.network.new << EOF
[Match]
Name=${interface}

[Network]
Address=${address}/${prefix}
DNS=${DNS}

[Route]
Gateway=${gateway}
Metric=2048

EOF

  if ! diff -u /run/systemd/network/wwan.network{,.new}
  then
    mv /run/systemd/network/wwan.network{.new,}
    systemctl restart systemd-networkd
  fi
}

while true
do
  update_net && sleep 5 || sleep 1
done