makeImage.sh

#!/bin/bash
# A bash script to create a time machine disk image suitable for
# backups with OS X 10.6 (Snow Leopard)
# This script probably only works for me, so try it at your own peril!
# Use, distribute, and modify as you see fit but leave this header intact.
# (R) sunkid - September 5, 2009
# 
# This will create a time machine ready disk image named with your 
# computer's name with a maximum size of 600GB and copy it to 
# /Volumes/backup. The image "file" (it's a directory, really) will 
# contain the property list file that SL's TM needs.
# 
# sh  ./makeImage.sh 600 /Volumes/backup
# cp -pfr <computer name>.sparsebundle /Volumes/backup/<computer name>.sparsebundle
# 
#
#
# Based on a script found here : 
# http://www.insanelymac.com/forum/index.php?showtopic=184462

usage ()
{
     echo ${errmsg}"\n"
     echo "usage: makeImage.sh SIZE [DIRECTORY]"
     echo "  Create a Time Machine disk image with a max storage SIZE GiB"
     echo "  at DIRECTORY (current directory if not specified)"
}

# test if we have two arguments on the command line
if [ $# -lt 1 ]
then
    usage
    exit
fi

# see if there are two arguments and we can write to the directory
if [ $# == 2 ]
then
  if [ ! -d $2 ]
  then
    errmsg=${2}": No such directory"
    usage
    exit
  fi
  if [ ! -w $2 ]
  then
    errmsg="Cannot write to "${2}
    usage
    exit
  fi
fi

SIZE=$1
DIR=$2
NAME=`scutil --get ComputerName`;
# Note: `head -n 1` added so that the pipeline chain does not wait for
# system_profiler to run to completion (which can take a while)
UUID=`system_profiler | grep 'Hardware UUID' | head -n 1 | awk '{print $3}'`

if [ -n "$DIR" ]
then
  cd "$DIR"
fi

echo  "Generating ${SIZE} GB disk image: ${NAME}.sparsebundle ..."
hdiutil create -size ${SIZE}G -fs HFS+J -type SPARSEBUNDLE \
  -volname 'Time Machine Backups' "${NAME}.sparsebundle" >> /dev/null 2>&1
echo "  Done."

echo "Generating property list file with uuid $UUID ..."
cat >"${NAME}.sparsebundle"/com.apple.TimeMachine.MachineID.plist <<EOFPLIST
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>com.apple.backupd.HostUUID</key>
        <string>$UUID</string>
</dict>
</plist>
EOFPLIST
echo "  Done."

echo "Configuring Time Machine to backup to \"$DIR/${NAME}.sparsebundle\" ..."
sudo tmutil setdestination "`pwd`/${NAME}.sparsebundle"
echo "  Done."

echo "Finished! Happy backups!"

hh

system_profiler command takes a while to end so the system_profiler | grep 'Hardware UUID' | ... also takes ages.

Use instead:
system_profiler SPHardwareDataType | awk '/UUID/ { print $3; }'

(source: https://www.commandlinefu.com/commands/view/24201/get-hardware-uuid-in-mac-os-x)