Index: rdiff-backup.1
===================================================================
RCS file: /sources/rdiff-backup/rdiff-backup/rdiff-backup.1,v
retrieving revision 1.78
diff -u -r1.78 rdiff-backup.1
--- rdiff-backup.1	2 Jan 2006 20:29:25 -0000	1.78
+++ rdiff-backup.1	30 Jan 2006 16:39:09 -0000
@@ -201,6 +201,13 @@
 .B USERS AND GROUPS
 section for more information.
 .TP
+.BI "\-\-if-older-than " time_spec
+Skip the backup unless the most recent incremental backup is older
+than
+.IR time_spec .
+This can be used in conjunction with cron to easily automate backups
+for systems that are not always available.
+.TP
 .BI "\-\-include " shell_pattern
 Similar to
 .B \-\-exclude
Index: rdiff_backup/Main.py
===================================================================
RCS file: /sources/rdiff-backup/rdiff-backup/rdiff_backup/Main.py,v
retrieving revision 1.104
diff -u -r1.104 Main.py
--- rdiff_backup/Main.py	30 Dec 2005 07:00:32 -0000	1.104
+++ rdiff_backup/Main.py	30 Jan 2006 16:39:09 -0000
@@ -30,6 +30,7 @@
 action = None
 create_full_path = None
 remote_cmd, remote_schema = None, None
+if_older_than_string = None
 force = None
 select_opts = []
 select_files = []
@@ -44,6 +45,7 @@
 def parse_cmdlineoptions(arglist):
 	"""Parse argument list and set global preferences"""
 	global args, action, create_full_path, force, restore_timestr, remote_cmd
+	global if_older_than_string
 	global remote_schema, remove_older_than_string
 	global user_mapping_filename, group_mapping_filename, \
 		   preserve_numerical_ids
@@ -69,8 +71,8 @@
 		  "exclude-globbing-filelist-stdin", "exclude-mirror=",
 		  "exclude-other-filesystems", "exclude-regexp=",
 		  "exclude-special-files", "force", "group-mapping-file=",
-		  "include=", "include-filelist=", "include-filelist-stdin",
-		  "include-globbing-filelist=",
+		  "if-older-than=", "include=", "include-filelist=",
+		  "include-filelist-stdin", "include-globbing-filelist=",
 		  "include-globbing-filelist-stdin", "include-regexp=",
 		  "include-special-files", "include-symbolic-links",
 		  "list-at-time=", "list-changed-since=", "list-increments",
@@ -127,6 +129,7 @@
 			select_files.append(sys.stdin)
 		elif opt == "--force": force = 1
 		elif opt == "--group-mapping-file": group_mapping_filename = arg
+		elif opt == "--if-older-than": if_older_than_string = arg
 		elif (opt == "--include" or
 			  opt == "--include-special-files" or
 			  opt == "--include-symbolic-links"):
@@ -329,6 +332,13 @@
 	backup_set_select(rpin)
 	backup_warn_if_infinite_regress(rpin, rpout)
 	if prevtime:
+		if if_older_than_string:
+			try: time = Time.genstrtotime(if_older_than_string)
+			except Time.TimeException, exc: Log.FatalError(str(exc))
+			if time < prevtime:
+				Log("Previous backup newer than %s, skipping"
+				    % if_older_than_string, 2)
+				return
 		Time.setprevtime(prevtime)
 		rpout.conn.Main.backup_touch_curmirror_local(rpin, rpout)
 		backup.Mirror_and_increment(rpin, rpout, incdir)