#!/bin/bash
# id2hostname by Andrew Oakley www.aoakley.com Public Domain 2015
#
# Get (and optionally set) a hostname based on a unique hardware
# identifier. Use -h to read help text.
#
# Recommend you place this in /usr/local/sbin/
# Run it on 1st boot with (for example): sudo crontab -e
# @reboot sudo su - root -c 'if [ -f /etc/1stboot ]; then rm /etc/1stboot ; raspi-config --expand-rootfs ; id2hostname -s --reboot ; fi'
# Then sudo touch /etc/1stboot before imaging SD card

# Script name, program version date and current host name
versiondate='2016-03-16'
scriptname=`basename $0`
currname="$(cat /etc/hostname)"

# Path or URL to default config file. URLs must include http:// https:// ftp:// etc
# If you are using -s --serial then this can be blank, or anything
conffile='/etc/id2hostname.conf'
#conffile='http://www.cotswoldjam.org/downloads/setup/id2hostname.conf'

# $idpath is the path to the unique hardware ID. On the Raspberry Pi,
# the CID for the booted SD card can be found in /sys/block/mmcblk0/device/cid
# and the MAC address for eth0 is at /sys/class/net/eth0/address
# If you are using -s --serial then this can be blank, or anything
defaultidpath='/sys/block/mmcblk0/device/cid'
defaultserialpath='/sys/block/mmcblk0/device/serial'
idpath=$defaultidpath

# $workdir is the temporary/working directory. A subdirectory
# id2hostname/ is created and then deleted under this directory.
workdir='/tmp'

# Default values for commandline parameters
doreboot='false'
oldname='raspberrypi'
readmode='false'
testmode='false'
serialmode='false'
vebose='false'
quiet='false'
sethostname='false'

# Parse parameters
while [[ "${1:0:1}" == "-" ]]; do
  case "$1" in
    ("-h"|"--help")
      # Ruler - 70 columns ends ........................................... here V
      echo
      echo "$scriptname by Andrew Oakley http://www.aoakley.com Public Domain"
      echo "Usage: [ sudo ] $scriptname  [ OPTIONS ]"
      echo "Add $0 --reboot"
      echo "to /etc/rc.local to run at boot time"
      echo
      echo "Sets the hostname based on a unique hardware identifier - by default,"
      echo "the CID of a Raspberry Pi's booted SD card. New hostnames are read"
      echo "from a config file, by default /etc/$scriptname.conf , which"
      echo "contains a list of identifiers, followed by a space, followed by the"
      echo "new hostname, one per line. For example:"
      echo
      echo "7342474e436172641012c2073800c400 teacher"
      echo "1b534d303030303010319106b700e700 pupil01"
      echo "035344535530324780202411de007800 pupil02"
      echo
      echo "You can find your Raspberry Pi's SD card's unique ID by doing:"
      echo "cat /sys/block/mmcblk0/device/cid"
      echo "Not got unique CIDs? Buy branded SD cards from good manufacturer!"
      echo "Not got a Raspberry Pi? Use the --id parameter and MAC address, eg:"
      echo "cat /sys/class/net/eth0/address"
      echo
      echo "The typical use case is where a teacher clones many SD cards for a"
      echo "classroom of Raspberry Pi computers. By setting the hostname for"
      echo "each card, the teacher can address each machine individually over"
      echo "the network, for example: ssh pi@pupil02 , provided zeroconf is"
      echo "configured and running (which it is on Raspbian OS, as avahi)."
      echo "On some distros, you may have to use pupil02.lan or pupil02.local ."
      echo
      echo "Note that this correctly changes both /etc/hostname *AND* /etc/hosts"
      echo "as changing /etc/hostname alone without /etc/hosts harms networking."
      ehoc "However the script does not reconfigure services such as web servers,"
      ehoc "email servers and so forth, which may need manual reconfiguration."
      echo
      echo "You can have your config file hosted as a URL, for example:"
      echo "$scriptname -c 'http://www.cotswoldjam.org/downloads/setup/id2hostname.conf'"
      echo
      echo "Mandatory arguments to long options are mandatory for short options too."
      echo "--version           Version and author information (for bug reports)"
      echo "-h, --help          Show this help text then exit"
      echo "-i, --id filepath   File containing unique hardware ID;"
      echo "                    default /sys/block/mmcblk0/device/cid"
      echo "                    also consider /sys/class/net/eth0/address"
      echo "-c, --conf file|url Configuration file; default /etc/$scriptname.conf"
      echo "                    You must have curl installed to use a URL"
      echo "-o, --oldname name  Old hostname to change; default raspberrypi"
      echo "                    Name won't be changed unless this matches the"
      echo "                    existing hostname. Set -o '' (empty string) to"
      echo "                    change hostname regardless (combining -c URL -o ''"
      echo "                    on every boot will mean slow boot times)."
      echo "-r, --read          Show the unique hardware ID, then exit without"
      echo "                    changing hostname (e.g. to copy & paste to .conf file"
      echo "                    or pipe to a custom script)"
      echo "-s, --serial        (RPi only) Append last 4 digits of CID serial to"
      echo "                    hostname. Use with --sethostname or default rpi-XXXX"
      echo "-t, --test          Display new name but don't actually set it"
      echo "-v, --verbose       Verbose mode"
      echo "-q, --quiet         Quiet mode (ignored with -r or -t)"
      echo "-w, --workdir dir   Working/temporary directory; default /tmp"
      echo "--reboot            Reboot after setting new hostname"
      echo "--sethostname name  Just set the hostname, ignoring id & config"
      echo "                    (also implies -o '' )"
      echo
      exit 0
    ;;
    ("--version")
      echo "$scriptname by Andrew Oakley http://www.aoakley.com Public Domain"
      echo "This version dated $versiondate"
      exit 0
    ;;
    ("-i"|"--id")
      shift
      idpath="$1"
      shift
    ;;
    ("-c"|"--conf")
      shift
      conffile="$1"
      shift
    ;;
    ("-o"|"--oldname")
      shift
      oldname="$1"
      shift
    ;;
    ("-r"|"--read")
      shift
      readmode='true'
      if [[ "$testmode" == "true" ]]; then
        [[ "$quiet" == "false" ]] && echo "You may not mix --read and --test" >&2
        exit 1
      fi
    ;;
    ("-s"|"--serial")
      shift
      serialmode='true'
    ;;
    ("-t"|"--test")
      shift
      testmode='true'
      if [[ "$readmode" == "true" ]]; then
        [[ "$quiet" == "false" ]] && echo "You may not mix --read and --test" >&2
        exit 1
      fi
    ;;
    ("-v"|"--verbose")
      shift
      verbose='true'
      quiet='false'
    ;;
    ("-q"|"--quiet")
      shift
      quiet='true'
      verbose='false'
    ;;
    ("-w"|"--workdir")
      shift
      workdir="$1"
      shift
    ;;
    ("--reboot")
      shift
      doreboot='true'
    ;;
    ("--sethostname")
      shift
      sethostname="$1"
      shift
      if [[ "$sethostname" == "" ]]; then
        [[ "$quiet" == "false" ]] && echo "No hostname supplied with --sethostname" >&2
        exit 2
      fi
    ;;
    (*)
      [[ "$quiet" == "false" ]] && echo "Invalid parameter: $1" >&2
      [[ "$verbose" == "true" ]] && echo "Try --help" >&2
      exit 1
  esac
done

if [[ ! -f '/etc/hostname' || ! -f '/etc/hosts' ]]; then
  [[ "$quiet" == "false" ]] && echo -e "Your distro doesn't appear to use /etc/hosts or\n/etc/hostname. $scriptname is not for you." >&2
  exit 3
fi

if [[ "$sethostname" == "false" ]]; then
  # Find unique ID
  if [[ ! -r "$idpath" ]]; then
    [[ "$quiet" == "false" ]] && echo "'$idpath' does not exist or is not readable" >&2
    [[ "$verbose" == "true" ]] && [[ "$idpath" == "$defaultidpath" ]] && echo "Not on a Raspberry Pi? See --help about --id" >&2
    exit 4
  fi
  myid=`cat $idpath`
  if [[ "$readmode" == "true" ]]; then
    echo "$myid"
    exit 0
  fi
  [[ "$verbose" == "true" ]] && echo "My unique ID: '$myid'"

  # Check for oldname
  if [[ -z "$oldname" || "$oldname" == "$currname" || "$testmode" == "true" ]]; then
  
    # Fetch newname
    if [[ "$serialmode" == "true" ]]; then
      newname="rpi-`cat $defaultserialpath | cut -c 7-10`"
    elif [[ -z "$(echo $conffile | grep '://')" ]]; then
      [[ "$verbose" == "true" ]] && echo "Reading from file: '$conffile'"
      newname=`grep "$myid" "$conffile" | cut -d\  -f 2`
    else
      [[ "$verbose" == "true" ]] && echo "Reading from URL: '$conffile'"
      newname=`curl -s "$conffile" | grep "$myid" | cut -d\  -f 2`
    fi
  
    if [[ -z "$newname" ]]; then
      [[ "$verbose" == "true" ]] && echo "Can't find '$myid' in '$conffile' - nothing to do"
      exit 0
    fi
  else
    [[ "$verbose" == "true" ]] && echo -e "Current hostname '$currname' is not old name '$oldname' - nothing to do\nUse -o '' to force a hostname change regardless."
    exit 0
  fi
else
  if [[ "$serialmode" == "true" ]]; then
    newname="$sethostname`cat $defaultserialpath | cut -c 7-10`"
  else
    newname=$sethostname
  fi
fi

if [[ "$testmode" == "true" ]]; then
  if [[ "$verbose" == "true" ]]; then
    if [[ "$newname" == "$currname" ]]; then
      echo "Host name should be: '$newname' (it already is)"
    else
      echo "New host name should be: '$newname'"
    fi
  else
    echo "$newname"
  fi
  exit 0
fi
if [[ "$newname" == "$currname" ]]; then
  if [[ "$currname" == "$(hostname)" ]]; then
    [[ "$verbose" == "true" ]] && echo "Hostname already set to '$newname' - nothing to do"
  else
    if [[ "$doreboot" == "false" ]]; then
      [[ "$verbose" == "true" ]] && echo "Hostname already set to '$newname' - reboot to apply change"
    else
      [[ "$quiet" == "false" ]] && echo "Rebooting to apply new hostname '$newname'..."
      shutdown -r now
    fi
  fi
  exit 0
fi

if [[ "$(id -u)" != 0 ]]; then
  [[ "$quiet" == "false" ]] && echo "Not root, so cannot set new hostname '$newname'" >&2
  [[ "$verbose" == "true" ]] && echo "use sudo $scriptname to solve this problem" >&2
  exit 5
fi

[[ "$verbose" == "true" ]] && echo "Setting new hostname: '$newname'"
mkdir -p "$workdir/id2hostname"
cd "$workdir/id2hostname"
echo "$newname" > newname.txt && awk "BEGIN{getline l < \"newname.txt\"}/$currname/{gsub(\"$currname\",l)}1" /etc/hosts | sudo tee newhosts.txt >/dev/null && sudo mv -f newhosts.txt /etc/hosts && sudo mv -f newname.txt /etc/hostname
rm -r "$workdir/id2hostname"

if [[ "$doreboot" == "true" ]]; then
  [[ "$quiet" == "false" ]] && echo "Hostname changed to '$newname'. Rebooting..."
  shutdown -r now
else
  [[ "$quiet" == "false" ]] && echo "Hostname changed to '$newname'. Reboot to apply change."
fi

exit 0