hostrename

#! /bin/bash
# hostrename (BASH script) -- portable host rename tool
#
# Version: 0.6
# Copyright: (c) 2015 Alastair Irvine <alastair@plug.org.au>
# Keywords: hostname
# See: 
# Licence: This file is released under the GNU General Public License
#
# See show_help() for usage.
#
# Thanks to the following:
#   + https://wiki.debian.org/HowTo/ChangeHostname
#   + http://www.itzgeek.com/how-tos/linux/centos-how-tos/change-hostname-in-centos-7-rhel-7.html#axzz3PFs3EXN8 
#   + http://www.cyberciti.biz/faq/centos-hostname-change-command-line/ 
#   
#
# Licence details:
#     This program is free software; you can redistribute it and/or modify
#     it under the terms of the GNU General Public License as published by
#     the Free Software Foundation; either version 2 of the License, or (at
#     your option) any later version.
#
#     See http://www.gnu.org/licenses/gpl-2.0.html for more information.
#
#     You can find the complete text of the GPLv2 in the file
#     /usr/share/common-licenses/GPL-2 on Debian systems.
#     Or see the file COPYING in the same directory as this program.
#
#
# TO-DO:
#  + look for "name ...." in /var/lib/bluetooth/11:11:11:11:11:11/config
#  + update_hosts_file():
#      use the actual IP address instead of 127.0.1.1 when adding a hostname entry

## /bin/hostnamectl set-hostname --static <x>

self=hostrename
allowed_options=mhdv
allowed_long_options=use-mailname,help,verbose::,debug::


# *** FUNCTIONS ***
show_help()
{
  cat << EOT_HELP
Usage: $self [-m | --use-mailname] <new_hostname> [<new_mailname>]
EOT_HELP
}


# Sets <$1> to $2, or increases <$1> if $2 is absent.
numeric_opt()
{
  # sanitise the value by aggressively stripping off a non-numeric suffix
  local value=${2%%[^0-9]*}

  if [ -z "$value" ] ; then
    eval "$1=\$(($1 + 1))"
  else
    eval "$1=$value"
  fi
}


# Make copies of a config file pointed to by a variable, "back up" the variable
# contents and then change it to point to the copied file.
make_fake()
{
  local location=$2
  local file copy

  # make a convenience copy of the variable and back up the contents
  eval file=\$$1
  eval real_$1=$file

  if [ -f $file ] ; then
    alternate_file=$location/${file##*/}
    cp -p $file $alternate_file
  fi

  # change the variable
  eval $1=$alternate_file
}


alter_copies()
{
  # Create copies of the config files and modify them instead
  rm -rf /tmp/$self.$$
  mkdir /tmp/$self.$$
  make_fake sysconfig_network_file /tmp/$self.$$
  make_fake hostname_file /tmp/$self.$$
  make_fake hosts_file /tmp/$self.$$
  ## sed --in-place "/^127\.0\.1\.1\>/ d" $hosts_file
  ## if grep --quiet -F ^127.0.1.1 $hosts_file 
  ## then
  ##   echo 127.0.1.1 is still there!
  ##   exit 19
  ## fi
  make_fake mailname_file /tmp/$self.$$
  echo modified files in /tmp/$self.$$
}


# Updates /etc/hosts to add or change the hostname
# If $use_mailname is set to y, $mailname will be included as an alias
update_hosts_file()
{
  local hosts_sed_subst="$longname $([ "$use_mailname" = y ] && echo "$mailname ")$shortname"

  # check for a fake localhost address
  # (for rationale on 127.0.1.1, see http://qref.sourceforge.net/quick/ch-gateway.en.html )
  if grep --quiet '^127\.0\.1\.1\>' $hosts_file
  then
    sed --in-place=.old "s/^127\.0\.1\.1\>.*/127.0.1.1\t$hosts_sed_subst/" \
      $hosts_file
  elif [ $oldhostname != localhost ] && [ $oldhostname != localhost.localdomain ] && \
       grep --quiet "^[^#]*\<${oldhostname//./\\.}\>" $hosts_file
  then
    # There's a static entry, so replace that.
    # replace the hostname (with dots quoted) leaving the IP address intact
    sed --in-place=.old "/^[^#]*\<${oldhostname//./\\.}\>/ s/^\([^[:space:]]*\).*/\1\t$hosts_sed_subst/" \
      $hosts_file
  else
    # There isn't currently a hostname entry in $hosts_file, so add one after
    # the localhost entry
    sed --in-place=.old "/^127\.0\.0\.1\>/ a\
127.0.1.1\t$hosts_sed_subst" \
      $hosts_file
  fi
}


# *** MAINLINE ***
# == Command-line parsing ==
# (1st arg was already used as the action (and discarded), if necessary)

# -- defaults --
hosts_file=/etc/hosts
hostname_file=/etc/hostname
sysconfig_network_file=/etc/sysconfig/network
mailname_file=/etc/mailname
use_mailname=n
debug=0
verbose=0

# -- option handling --
set -e
orthogonal_opts=$(getopt --shell=sh --name=$self \
  --options=+$allowed_options --longoptions=$allowed_long_options -- "$@")

cmd_line=$*
eval set -- "$orthogonal_opts"
set +e      # getopt would have already reported the error

while [ x"$1" != x-- ] ; do
  ## echo "option: $1 [$2]"
  # Note: absent optional arguments for long options are replaced with the empty string

  case "$1" in
    -m|--use-mailname) use_mailname=y ;;
    -h|--help)    show_help ; exit ;;
    -d)      debug=$((debug + 1)) ;;
    --debug) numeric_opt debug "$2" ; shift ;;
    -v)        verbose=$((verbose + 1)) ;;
    --verbose) numeric_opt verbose "$2" ; shift ;;
  esac
  shift       # get rid of the option (or its arg if the inner shift removed the option)
done
shift       # get rid of the "--"
[ $debug -ge 3 ] && echo "command line: $cmd_line"
[ $debug -ge 2 ] && echo "opts: $orthogonal_opts"

# -- argument handling --
if [ $# -lt 1 -o $# -gt 2 ] ; then
  echo "${self}: Error: Invalid arguments" >&2
  show_help
  exit 1
fi

# check for dot in hostname
if echo $1 | grep --quiet -F .
then
  shortname=${1%%.*}
  longname=$1
else
  shortname=$1
  longname=$1.$(dnsdomainname)
  echo "${self}: Warning: hostname is not fully qualified; assuming $longname" >&2
fi

if [ -z "$2" ] ; then
  mailname=$longname
else
  mailname=$2
fi


# == sanity checking ==
if [ "$use_mailname" = y -a -z "$mailname" ] ; then
  echo "${self}: Error: mailname argument not supplied, but required by option" >&2
  exit 1
fi


# == Preparation ==
oldhostname=$(hostname)
[ $debug -ge 2 ] && alter_copies


# == Processing ==
[ $debug -ge 1 ] && echo verbose=$verbose and debug=$debug

if [ $verbose -ge 1 ] ; then
  echo "renaming $oldhostname to $longname"
  if [ $verbose -ge 2 ] ; then
    echo "(shortname = '$shortname'; mailname = '$mailname')"
  fi
fi

[ $debug -ge 3 ] && exit

# check for systemd present
if [ -x /bin/hostnamectl ] ; then
  hostnamectl set-hostname $longname
  update_hosts_file
else
  # Check for RedHat or Amazon Linux
  if [ -f /etc/redhat-release -o -f /etc/system-release ] ; then
    if [ -x /usr/bin/nmcli ] ; then
      # assume that Network Manager can rename the hostname
      nmcli general hostname $longname
    else
      sed --in-place=.old "s/^HOSTNAME=.*/HOSTNAME=$longname/" \
        $sysconfig_network_file
      update_hosts_file
    fi

    # TO-DO: check for Postfix and if so, edit /etc/postfix/main.cf as follows:
    #   + myhostname = $longname
    #   + myorigin   = $mailname

    # RedHat handles this differently to Debian
    hostname $longname

  elif [ -f /etc/debian_version ] ; then
    cp -p $hostname_file $hostname_file.old 2> /dev/null
    echo $shortname > $hostname_file
    update_hosts_file

    # Update /etc/mailname if it doesn't exist or if $mailname is different
    if [ ! -f /etc/mailname -o -n "$mailname" ] ; then
      # TO-DO: handle the case where the mailname doesn't correspond to the old hostname
      if [ "$(cat /etc/mailname 2> /dev/null)" != "$mailname" ] ; then
        cp -p $mailname_file $mailname_file.old 2> /dev/null
        echo $mailname > $mailname_file
      fi
    fi
    # TO-DO: check for Postfix and if so, edit /etc/postfix/main.cf as follows:
    #   + myhostname = $longname

    # RedHat handles this differently to Debian
    hostname $shortname
  fi
fi