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+#!/bin/bash
+#
+# rsync-backup.sh - a backup script using rsync.
+#
+# Copyright 2017, 2018 Einhard Leichtfuß
+#
+# This file is part of rsync-backup.
+#
+# rsync-backup is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published
+# by the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# 
+# rsync-backup is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+# 
+# You should have received a copy of the GNU Affero General Public License
+# along with rsync-backup.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+RSYNC=rsync
+
+typeset -a rsync_args
+typeset -a rsync_inc_args
+typeset -A bakpath
+typeset filter_file_all
+typeset -A filter_file
+
+# Default arguments for rsync.
+rsync_args=(
+	--recursive
+	--perms --times --owner --group
+	#--acls --xattrs
+	--links
+	--hard-links
+	--sparse
+	--timeout=60
+	-vv
+	)
+
+# Supplemental arguments for rsync; only used when an actual incremental
+# update is performed, i.e. when --link-dest is used.
+rsync_inc_args=(
+	--fuzzy --fuzzy
+	)
+
+filter_file_all=/etc/rsync-backup/filter
+
+config=/etc/rsync-backup/backup.conf
+source "$config"
+
+src=/home/respiranto/txt/bash/rsync-backup/src
+dest=/home/respiranto/txt/bash/rsync-backup/dest
+
+typeset -l reply
+typeset -i i n
+
+# RSYNC args.
+# basic args:  --recursive --perms --times --owner --group --links
+# extra args:  --sparse --acls --xattrs --hard-links --timeout=60
+#              --fuzzy --fuzzy
+#              --filter="merge <file>"
+# likely:      --compress
+#              --partial{,dir=DIR}
+#              --progress
+# possibly:    --devices --specials
+#              --max-size=SIZE-OF-FILE
+#              --one-file-system 
+#              --log-file=FILE --log-file-format=FORMAT
+#              --human-readable
+# unlikely:    --omit-{dir,link}-times --update (!--inplace) --delete
+#              --exclude
+# great:       --link-dest=DIR (timestamps?)
+# testing:     --verbose --dry-run (-vn)
+# interesting: --sockopts --itemize-changes --out-format=FORMAT
+#              --stats
+
+function main
+{
+	# In case of a non-matching wildcard, return nothing.
+	shopt -s nullglob
+	# Include dotfiles (except . and ..) in regex matching.
+	shopt -s dotglob
+
+	get_args "$@" || return $?
+
+	check_paths || return $?
+
+	# Change the separation char to $'\n' to avoid confusion with filenames
+	# containing spaces (default is $' \t\n').
+	IFS=$'\n'
+
+	find_existing_backup_dirs || return $?
+
+	perform_backup || return $?
+
+	refresh_symlinks || return $?
+}
+
+
+function get_args
+{
+	if [ $# -eq 0 ]
+	then
+		echo "Usage: $0 <src> [<dest>]"
+		return 1
+	fi
+
+	dirpath="$(realpath "$1")"
+
+	if [ $# -gt 1 ]
+	then
+		bakpath="$(realpath $2)"
+	elif test -v bakpath[$dirpath]
+	then
+		bakpath="${bakpath[$dirpath]}"
+	else
+		echo "Error: Backup path for $dirpath not configured."
+		return 1
+	fi
+
+	filter_args=()
+	if test -v filter_file_all -a -f "$filter_file_all"
+	then
+		filter_args=("--filter=merge ${filter_file_all}")
+	fi
+	if test -v filter_file[$dirpath] && test -f "${filter_file[$dirpath]}"
+	then
+		filter_args+=("--filter=merge ${filter_file[$dirpath]}")
+	fi
+}
+
+
+function check_paths
+{
+	# Test whether the dirs exist already.
+	if ! test -d "$dirpath"
+	then
+		echo "Source (\"$dirpath\") does not exist."
+		return 1
+	fi
+
+	if ! test -d "$bakpath"
+	then
+		echo "Target (\"$bakpath\") does not exist."
+		echo -n "Do you want do create it [y/N]? "
+		read reply
+		if [[ "$reply" != "y" && "$reply" != "yes" ]]
+		then
+			return 1
+		fi
+
+		if ! mkdir -p "$bakpath"
+		then
+			echo "Backup creation has failed."
+			echo "\"$bakpath\" could not be created."
+			return 1
+		fi
+	fi
+}
+
+
+function find_existing_backup_dirs
+{
+	n=0
+	for file in `ls "$bakpath"`; do
+		if test -d $bakpath/$file \
+			&& [[ "$file" =~ ^[0-9]{4}-[0-1][0-9]-[0-3][0-9]_[0-2][0-9]([0-5][0-9]){2}.backup$ ]]
+		then
+			dirs[n]="$file"
+			n+=1
+		fi
+	done
+}
+
+
+# $1 path
+# $2 error message: string
+function clear_file
+{
+	if test -e "$1" -o -L "$1"; then
+		echo "It seems like the last backup process failed or you have created" \
+		 	"the file \"$1\" manually."
+		echo -n "Do you want to delete it [y/N]? "
+		read reply
+		if [[ "$reply" == "y" || "$reply" == "yes" ]]
+		then
+			printf "Deleting"
+			if rm -rf "$1"; then
+				printf " - done\n"
+				return 0
+			else
+				printf '\n%s\n' "$2"
+				printf 'The file \"%s\" could not be deleted.\n' "$1"
+				return 1
+			fi
+		else
+			printf '%s\n' "$2"
+			printf '%s %s\n' "Please remove the above mentioned file manually" \
+				"or run this script once more."
+			return 1
+		fi
+	fi
+	return 0
+}
+
+
+function perform_backup
+{
+	bakdate=`date +%Y-%m-%d_%H%M%S.backup`
+	finaldir="$bakpath/$bakdate"
+	tempdir="$bakpath/new.backup"
+	clear_file "$tempdir" "Backup creation has failed." || return 1
+	clear_file "$finaldir" "Backup creation has failed." || return 1
+
+	# note: $n == ${#dirs[@]}
+	printf 'Starting backup nr. %u.\n' "$n"
+	if [ $n -eq 0 ]
+	then
+		# Perform first backup, not incremental.
+		$RSYNC "${rsync_args[@]}" \
+			"${filter_args[@]}" \
+			"$dirpath"/ "$tempdir" \
+			|| return 1
+	else
+		# Perform incremental backup on the basis of the last.
+		$RSYNC "${rsync_args[@]}" \
+			"${rsync_inc_args[@]}" --link-dest="${bakpath}/${dirs[n-1]}" \
+			"${filter_args[@]}" \
+			"$dirpath"/ "$tempdir" \
+			|| return 1
+	fi
+
+	mv "$tempdir" "$finaldir" || return 1
+	printf '\nCreating of backup nr. %u succesfully executed.\n' "$n"
+}
+
+
+function refresh_symlinks
+{
+	linkdir="$bakpath/latest"
+	if test -L "$linkdir"
+	then
+		rm "$linkdir"
+		ln -s "$bakdate" "$linkdir"
+	elif clear_file "$linkdir" "Creation of softlink \"$linkdir\" failed."
+	then
+		ln -s "$bakdate" "$linkdir"
+	fi
+
+	# by_number
+	numdir="$bakpath/by_number"
+	if ! test -d "$numdir"
+	then
+		if clear_file "$numdir" "Creating directory $numdir failed."
+		then
+			mkdir "$numdir"
+		else
+			return 1
+		fi
+	fi
+
+	for file in "$numdir"/*
+	do
+		if test -L "$file"
+		then
+			rm "$file"
+		else
+			if ! clear_file "$file" "Setting up numbered softlinks failed."
+			then
+				return 1
+			fi
+		fi
+	done
+
+	dirs[$n]="$bakdate" # Set last dir on current.
+	max_n_zeros=$((${#n} - 1))
+	i=1
+	while [ $i -le $max_n_zeros ]
+	do
+		zeros[i]=$(printf '%.s0' {$i..$max_n_zeros})
+		i+=1
+	done
+
+	i=0
+	while [ $i -le $n ]
+	do
+		ln -s "../${dirs[i]}" "$numdir/${zeros[${#i}]}$i"
+		i+=1
+	done
+}
+
+
+main "$@"