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dnsmasq 2.84

#!/bin/bash

STATUS_FILE="/tmp/dnsmasq-ip-mac.status"

# Script for dnsmasq lease-change hook.
# Maintains the above file with an IP address/MAC address pairs,
# one lease per line. Works with IPv4 and IPv6 leases, file is
# atomically updated, so no races for users of the data.

action="$1"
mac="$2"   # IPv4
ip="$3"

# ensure it always exists.

if [ ! -f "$STATUS_FILE" ]; then
  touch "$STATUS_FILE"
fi

if [  -n "$DNSMASQ_IAID" ]; then
    mac="$DNSMASQ_MAC"   # IPv6
fi

# worry about an add or old action when the MAC address is not known:
# leave any old one in place in that case.

if [ "$action" = "add" -o "$action" = "old" -o "$action" = "del" ]; then
  if [ -n "$mac" -o "$action" = "del" ]; then
    sed "/^${ip//./\.} / d" "$STATUS_FILE" > "$STATUS_FILE".new
  
    if [ "$action" = "add" -o "$action" = "old" ]; then
       echo "$ip $mac" >> "$STATUS_FILE".new
    fi
    mv  "$STATUS_FILE".new "$STATUS_FILE" # atomic update.
  fi
fi