change_hostname.sh

#!/bin/bash
####################################################################################################
#
#   Change host name
#
####################################################################################################
#
# HISTORY
#
#   Version 1.0, 27-Mar-2018, Graham Pugh.
#   Version 2.0, 15-Jun-2018, Graham Pugh. Added wait for network. Added verbosity to output. Set hostname to FQDN.
#   Version 3.0, 28-Aug-2018, Graham Pugh. Grab DNS name from A record using `host` command.

####################################################################################################

# Domain name
domain="company.com"

# Docking network string
docking="docking"

# Max time to wait for a DNS name (seconds)
countermax=60

# DON'T EDIT BELOW HERE

# Get current ComputerName
computerName=$( scutil --get ComputerName )
localHostName=$( scutil --get LocalHostName )
hostName=$( scutil --get HostName )

# Get current hostname from DNS
IP=$(ifconfig | grep "inet " | grep -m 1 -v 127.0.0.1 | cut -d ' ' -f2)
hostNamefromARecord=$(host $IP | rev | cut -d ' ' -f1 | rev | sed -e 's|\.$||')

# Check for FQDN, wait for network if necessary up to countermax limit
counter=0
while [[ $counter -lt $countermax && $hostNamefromARecord != *$domain* ]]; do
    IP=$(ifconfig | grep "inet " | grep -m 1 -v 127.0.0.1 | cut -d ' ' -f2)
    hostNamefromARecord=$(host $IP | rev | cut -d ' ' -f1 | rev | sed -e 's|\.$||')

    [[ $hostNamefromARecord == *$domain* ]] && break

    echo "[$( date )] DNS name not found. Waiting for a connection..."

    counter=$[${counter}+10]
    echo "[$( date )] Waiting for a valid DNS name... ${counter} seconds"
    sleep 10
done

# Valid FQDN name returned
if [[ ${hostNamefromARecord} == *$domain* && ${hostNamefromARecord} != *$docking* ]]; then
    echo "[$( date )] FQDN found from $domain domain."
    if [[ "${hostName}" == "${hostNamefromARecord}" ]]; then
        echo "[$( date )] hostName already set to '${hostName}'"
    else
        echo "[$( date )] HostName changing from '${hostName}' to '${hostNamefromARecord}'"
        scutil --set HostName "${hostNamefromARecord}"
    fi
    hostName=$hostNamefromARecord
# Invalid name returned
elif [[ ${hostNamefromARecord} == *$domain* && ${hostNamefromARecord} == *$docking* ]]; then
    echo "[$( date )] Computer connected to docking network. Using $hostName."
elif [[ $hostName ]]; then
    echo "[$( date )] No FQDN found from $domain domain. Using $hostName."
# No HostName at all so need to quit
else
    echo "[$( date )] No FQDN found from $domain domain, and no HostName set. Cannot proceed to change local hostnames."
    exit 1
fi

# We have a HostName, so check and repair ComputerName and LocalHostName as necessary
if [[ "${computerName}" == "${hostName%%.*}" ]]; then
    echo "[$( date )] ComputerName already set to '${computerName}'"
else
    echo "[$( date )] ComputerName changing from '${computerName}' to '${hostName%%.*}'"
    scutil --set ComputerName "${hostName%%.*}"
fi

if [[ "${localHostName}" == "${hostName%%.*}" ]]; then
    echo "[$( date )] LocalHostName already set to '${localHostName}'"
else
    echo "[$( date )] LocalHostName changing from '${localHostName}' to '${hostName%%.*}'"
    scutil --set LocalHostName "${hostName%%.*}"
fi