add hostmac

diff --git a/hostmac b/hostmac
new file mode 100755 (executable)
index 0000000..2402fd4
--- /dev/null
+++ b/hostmac
@@ -0,0 +1,39 @@
+#!/bin/bash
+# Copyright (C) 2016 Ian Kelling
+
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+
+#     http://www.apache.org/licenses/LICENSE-2.0
+
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eE -o pipefail
+trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR
+
+case $1 in
+    -h|--help)
+        cat <<'EOF'
+Usage: hostmac HOST
+Get a host's mac address
+
+If it's not in ip a, then ping it and look in the arp cache.
+EOF
+        exit 0
+        ;;
+esac
+host=$1
+
+ip=$(host $host | sed -rn 's/^\S+ has address //p')
+
+# first sed joins ip a paragraphs into a single line.
+if ip a | sed -r '1{x;d};/^[0-9]/{: p;x;s/\n//g;b};$b p;H;d' \
+        | sed -rn "/${ip//./\\.}/{s#^.*link/ether\s(\S+)\s.*#\1#p;q1}"; then
+    ping -c1 $ip &>/dev/null
+    arp -n $ip | tail -n+2 | awk '{print $3}'
+fi