#!/bin/bash
# ----------------------------------------------------------------------
# e-head's backup script 
# (adapted from mikes handy rotating-filesystem-snapshot utility)
# ----------------------------------------------------------------------
# intended to be run as a cron job 
#
# ------------- defaults (edit this) -----------------------------------------

# if you feel safer "hardcoding" the source and snapshot directories do it here.
# then just comment out the relavant sections of the while getopts loop below and
# also comment out the error checking section

# source directory, e.g.
# SRC=/home/

# dest (snapshot location), e.g.
# SNAPSHOTS=/mnt/hdb2/scratch/bak/prague/home
# SNAPSHOTS=username@remotemachine.com:/path/to/destination/

# exclude these files
EXCLUDES=

# number of backups
NUMBK=4

# confirm ? you will be prompted by default.
y=false

# remote shell to be used if the SRC is on another computer
RSH=

# ------------- commands used by this script --------------------
# I have no idea why everybody wacks the path in scripts like this ...
# but mikes original did this, so I guess I will too ...
unset PATH

ID=/usr/bin/id
ECHO=/bin/echo
MOUNT=/bin/mount
RM=/bin/rm
MV=/bin/mv
CP=/bin/cp
TOUCH=/bin/touch
RSYNC=/usr/bin/rsync
EXPR=/usr/bin/expr
MKDIR=/bin/mkdir

# -------------- process options ---------------------------------
while getopts yhm:s:d:n:x:e: opt
do
	case "$opt" in
		s)  SRC=${OPTARG%/}/;;
		d)  SNAPSHOTS=$OPTARG;;
		n)  NUMBK=$OPTARG;;
		e)  RSH="--rsh=$OPTARG";;
		x)  EXCLUDES="--exclude-from=$OPTARG";;
		y)  y=true;;
		h | *)     # unknown flag
			echo >&2 \
			"usage: $0 [-hy] -s source -d snapshot_directory [-e remote_shell] [-n number_of_snapshots] [-x exclude_file]"
			exit 1;;
	esac
done
shift $(($OPTIND - 1))

# ------------- simple error checking -----------------------------

[ "$SRC" = "" ] || [ "$SNAPSHOTS" = "" ] || \
[ ! -d "$SNAPSHOTS" ] && {
	echo "usage: $0 [-hy] -s source -d snapshot_directory [-e remote_shell] [-n number_of_snapshots] [-x exclude_file]"
	exit 1
}

[ "$y" = "false" ] && {

echo -n \ "
source          $SRC
snapshot dir    $SNAPSHOTS
# snapshots     $NUMBK
exclude switch  $EXCLUDES

does this look right (Y/n)? "
read answer

case "$answer" in
	n | N ) exit 0;;
	y | Y | * ) echo "let's go !";;
esac
}
# ------------- back it up ! --------------------------------------


NUMBK=$($EXPR $NUMBK - 1)
X=$($EXPR $NUMBK - 1)

# make sure we're running as root
if (( `$ID -u` != 0 )); then { $ECHO "Sorry, must be root.  Exiting..."; exit; } fi

# step 1: delete the oldest snapshot, if it exists:
if [ -d "$SNAPSHOTS/snapshot.$NUMBK" ]; then
$RM -rf "$SNAPSHOTS/snapshot.$NUMBK"
fi

# step 2: shift the middle snapshots(s) back by one, if they exist
while [ "$X" -gt 0 ] 
do
if [ -d "$SNAPSHOTS/snapshot.$X" ]; then
$MV "$SNAPSHOTS/snapshot.$X" "$SNAPSHOTS/snapshot.$($EXPR $X + 1)"
fi
X=$(($X-1))
done

# step 3: make a hard-link-only (except for dirs) copy of
# snapshot.0, assuming that exists, into snapshot.1
if [ -d "$SNAPSHOTS/snapshot.0" ]; then
$CP -al "$SNAPSHOTS/snapshot.0" "$SNAPSHOTS/snapshot.1"
fi

# step 4: rsync from the system into the latest snapshot (notice that
# rsync behaves like cp --remove-destination by default, so the destination
# is unlinked first.  If it were not so, this would copy over the other
# snapshot(s) too!
[ ! -d "$SNAPSHOTS/snapshot.0" ] && $MKDIR "$SNAPSHOTS/snapshot.0"

$RSYNC \
-va --delete $RSH $EXCLUDES \
"$SRC" "$SNAPSHOTS/snapshot.0"

# step 5: update the mtime of hourly.0 to reflect the snapshot time
$TOUCH "$SNAPSHOTS/snapshot.0"