iankelling.org Git - small-misc-bash/blob - hostmac

   1 #!/bin/bash
   2 # Copyright (C) 2016 Ian Kelling
   3
   4 # Licensed under the Apache License, Version 2.0 (the "License");
   5 # you may not use this file except in compliance with the License.
   6 # You may obtain a copy of the License at
   7
   8 #     http://www.apache.org/licenses/LICENSE-2.0
   9
  10 # Unless required by applicable law or agreed to in writing, software
  11 # distributed under the License is distributed on an "AS IS" BASIS,
  12 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13 # See the License for the specific language governing permissions and
  14 # limitations under the License.
  15
  16 set -eE -o pipefail
  17 trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR
  18
  19 case $1 in
  20     -h|--help)
  21         cat <<'EOF'
  22 Usage: hostmac HOST
  23 Get a host's mac address
  24
  25 If it's not in ip a, then ping it and look in the arp cache.
  26 EOF
  27         exit 0
  28         ;;
  29 esac
  30 host=$1
  31
  32 ip=$(host $host | sed -rn 's/^\S+ has address //p')
  33
  34 # first sed joins ip a paragraphs into a single line.
  35 if ip a | sed -r '1{x;d};/^[0-9]/{: p;x;s/\n//g;b};$b p;H;d' \
  36         | sed -rn "/${ip//./\\.}/{s#^.*link/ether\s(\S+)\s.*#\1#p;q1}"; then
  37     ping -c1 $ip &>/dev/null
  38     arp -n $ip | tail -n+2 | awk '{print $3}'
  39 fi