A small script for use in ssh-config Match statements.

ether-match

#! /bin/bash
#
# Usage in ~/.ssh_config, usefull RPi defaults:
#
# Match exec "ether-match %h 'b8:27:eb:*'"
#     User pi
#     ForwardX11 no
#     CheckHostIP no
#     StrictHostKeyChecking no

host="$1"

if [ -z "$host" ]; then
    exit 1
fi

if [[ "$host" =~ '^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$' ]]; then
    ip="$host"
else
    ip=$(getent ahostsv4 "$host" | head -n 1 | awk '{ print $1 }')
fi

arp_hwaddr=$(arp -n | awk '$1 == "'"$ip"'" && $2 == "ether" { print $3 }')

if [ -z "$arp_hwaddr" ]; then
    ping -c1 -W 1 -q -n "$ip" >& /dev/null 2>&1
    arp_hwaddr=$(arp -n | awk '$1 == "'"$ip"'" && $2 == "ether" { print $3 }')
fi

if [ -z "$arp_hwaddr" ]; then
    exit 1
fi

for ether in "$@"; do
    if [[ "$arp_hwaddr" == $ether ]]; then
        exit 0
    fi
done
  
exit 1