#!/bin/bash

# backup--Creates either a full or incremental backup of a set of
#   defined directories on the system. By default, the output 
#   file is compressed and saved in /tmp with a timestamped filename.
#   Otherwise, specify an output device (another disk, a removable 
#   storage device, or whatever else floats your boat).

compress="bzip2"    # Change to 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 here's an update of the timestamp.

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

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

########## Main code section begins here ###########

while getopts "o:ifn" arg; do
  case "$opt" in
    o ) output="$OPTARG";       ;;   # Getopts automatically manages 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')"  # Grab month,day,hour,minute from 'date'.
                                 # Curious about date formats? "man strftime"

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