initial commit with some functions, is not supposed to work yet, we need to provide some kind of configuration file and a sane way to procedurally read it

backup.zsh

@@ -0,0 +1,87 @@
+#!/usr/bin/env zsh
+# Default config file
+default_cfg='/usr/local/etc/backup.cfg'
+
+# Default date postfix
+default_postfix=$(date +%F-%H%M)
+
+function err
+{
+	[[ -n $2 ]] && echo $2 >&2
+	return $1
+}
+
+function default_ports
+{
+	if [[ -z $port_remote ]]; then
+		case $protocol in
+			('ftp') remote_port='21';;
+			('sftp'|'ssh') remote_port='22';;
+			(*) err 1 "$protocol is not a valid value for the protocol option.";;
+		esac
+	fi
+}
+
+function generate_fullpath
+{
+	src_basename=${src_fullpath:t}
+	src_basedir=${src_fullpath:h}
+	if [[ -s $snap_file ]]; then
+		backup_type='incr'
+	else
+		backup_type='full'
+	fi
+	if [[ -z $backup_directory && $protocol != 'ssh' ]]; then
+		err 1 "You have not set the backup directory path."
+	elif [[ -z $backup_filename ]]; then
+		outfile="$backup_directory/$host_local\-$src_basename\_$postfix\_$backup_type.t${compress_format:-ar}"
+	else
+		outfile=$backup_filename
+	fi
+}
+
+function compress # compress to stdout
+{
+	case $compress_format in
+		('xz') compress_flag='J' ;;
+		('bz2') compress_flag='j' ;;
+		('gz') compress_flag='z' ;;
+		('') unset compress_flag; unset compress_format ;;
+		(*) err 1 "$compress_format is not a valid value for the compression format option.";;
+	esac
+	if [[ -n $exclude_list ]]; then
+		if [[ -r $exclude_list ]]; then
+			exclude_option='-X'
+		else
+			err 1 "Exclusion list $exclude_list is either unreadable or does not exist."
+		fi
+	fi
+	if [[ -n $snap_file && -n $incremental_backup ]]; then
+		if printf '' >> $snap_file; then
+			snapshot_option='-g'
+		else
+			err 1 "Snapshot file $snap_file cannot be written."
+		fi
+	fi
+	tar cf$compress_flag - -C $src_basedir $src_basename $snapshot_option $snapshot_file $exclude_option $exclude_list --ignore-failed-read
+}
+
+function encrypt # encrypt if encryption is needed
+{
+	if [[ -n $gnupg_key ]]; then
+		gpg -r $gnupg_key -e -
+	else
+		read _
+		print $_
+	fi
+}
+
+function store # store to local or remote
+{
+	case $protocol in
+		('local') dd of=$outfile ;;
+		('ssh') ssh -p$port_remote $user_remote@$host_remote "dd of=$outfile" ;;
+		('sftp'|'ftp'|'ftps') curl -ksS -T - $protocol://$host_remote:$port_remote/$outfile -u $user_remote:$pass_remote ;;
+		(*) err 1 'Wrong protocol!' ;;
+	esac
+}