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

   1 #!/bin/bash
   2 # I, Ian Kelling, follow the GNU license recommendations at
   3 # https://www.gnu.org/licenses/license-recommendations.en.html. They
   4 # recommend that small programs, < 300 lines, be licensed under the
   5 # Apache License 2.0. This file contains or is part of one or more small
   6 # programs. If a small program grows beyond 300 lines, I plan to switch
   7 # its license to GPL.
   8
   9 # Copyright 2024 Ian Kelling
  10
  11 # Licensed under the Apache License, Version 2.0 (the "License");
  12 # you may not use this file except in compliance with the License.
  13 # You may obtain a copy of the License at
  14
  15 #     http://www.apache.org/licenses/LICENSE-2.0
  16
  17 # Unless required by applicable law or agreed to in writing, software
  18 # distributed under the License is distributed on an "AS IS" BASIS,
  19 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  20 # See the License for the specific language governing permissions and
  21 # limitations under the License.
  22
  23
  24 set -eE -o pipefail
  25 trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR
  26
  27 case $1 in
  28     -h|--help)
  29         cat <<'EOF'
  30 Usage: hostmac HOST
  31 Get a host's mac address
  32
  33 If it's not in ip a, then ping it and look in the arp cache.
  34 EOF
  35         exit 0
  36         ;;
  37 esac
  38 host=$1
  39
  40 ip=$(host $host | sed -rn 's/^\S+ has address //p')
  41
  42 # first sed joins ip a paragraphs into a single line.
  43 if ip a | sed -r '1{x;d};/^[0-9]/{: p;x;s/\n//g;b};$b p;H;d' \
  44         | sed -rn "/${ip//./\\.}/{s#^.*link/ether\s(\S+)\s.*#\1#p;q1}"; then
  45     ping -c1 $ip &>/dev/null
  46     arp -n $ip | tail -n+2 | awk '{print $3}'
  47 fi