#!/bin/sh

# Backup - create either a full or incremental backup of a set of
#     defined directories on the system. By default, the output 
#     file is saved in /tmp with a timestamped filename, compressed.
#     Otherwise, specify an output device (another disk, a removable).

usageQuit()
{
  cat << "EOF" >&2
Usage: $0 [-o output] [-i|-f] [-n]
  -o lets you specify an alternative backup file/device
  -i is an incremental or -f is a full backup, and -n prevents
  updating the timestamp if an incremental backup is done.
EOF
  exit 1
}

compress="bzip2"	# change for your favorite compression app
inclist="/tmp/backup.inclist.$(date +%d%m%y)"
 output="/tmp/backup.$(date +%d%m%y).bz2"
 tsfile="$HOME/.backup.timestamp"
  btype="incremental"	# default to an incremental backup
  noinc=0			#   and an update of the timestamp

trap "/bin/rm -f $inclist" EXIT

while getopts "o:ifn" opt; do
  case "$arg" in
    o ) output="$OPTARG";  	;;
    i ) btype="incremental";	;;
    f ) btype="full";		;;
    n ) noinc=1;		;;
    ? ) usageQuit		;;
  esac
done

shift $(( $OPTIND - 1 ))

echo "Doing $btype backup, saving output to $output"

timestamp="$(date +'%m%d%I%M')"

if [ "$btype" = "incremental" ] ; then 
  if [ ! -f $tsfile ] ; then
    echo "Error: can't do an incremental backup: no timestamp file" >&2
    exit 1
  fi
  find $HOME -depth -type f -newer $tsfile -user ${USER:-LOGNAME} | \
    pax -w -x tar | $compress > $output
  failure="$?"
else
  find $HOME -depth -type f -user ${USER:-LOGNAME} | \
    pax -w -x tar | $compress > $output
  failure="$?"
fi

if [ "$noinc" = "0" -a "$failure" = "0" ] ; then
  touch -t $timestamp $tsfile
fi

exit 0