1Jeremy Bornstein wrote:
2
3I recently had the need to transfer files only with different mod
4dates (and to *not* transfer them based on file size differences).
5This is because I'm backing up files remotely on an untrusted machine,
6so I'm encrypting them with gpg before transfer.  I discovered that
7rsync didn't already have a --date-only flag, so I added one and am
8enclosing the diffs in case you (as I hope) decide to include this
9option in future releases.
10
11To use this patch, run these commands for a successful build:
12
13    patch -p1 <patches/date-only.diff
14    ./configure                                 (optional if already run)
15    make
16
17--- old/generator.c
18+++ new/generator.c
19@@ -60,6 +60,7 @@ extern int append_mode;
20 extern int make_backups;
21 extern int csum_length;
22 extern int ignore_times;
23+extern int date_only;
24 extern int size_only;
25 extern OFF_T max_size;
26 extern OFF_T min_size;
27@@ -378,6 +379,8 @@ void itemize(struct file_struct *file, i
28 /* Perform our quick-check heuristic for determining if a file is unchanged. */
29 int unchanged_file(char *fn, struct file_struct *file, STRUCT_STAT *st)
30 {
31+	if (date_only)
32+		return cmp_time(st->st_mtime, file->modtime) == 0;
33 	if (st->st_size != file->length)
34 		return 0;
35 
36--- old/options.c
37+++ new/options.c
38@@ -99,6 +99,7 @@ int keep_partial = 0;
39 int safe_symlinks = 0;
40 int copy_unsafe_links = 0;
41 int size_only = 0;
42+int date_only = 0;
43 int daemon_bwlimit = 0;
44 int bwlimit = 0;
45 int fuzzy_basis = 0;
46@@ -343,6 +344,7 @@ void usage(enum logcode F)
47   rprintf(F,"     --timeout=TIME          set I/O timeout in seconds\n");
48   rprintf(F," -I, --ignore-times          don't skip files that match in size and mod-time\n");
49   rprintf(F,"     --size-only             skip files that match in size\n");
50+  rprintf(F,"     --date-only             skip files that match in mod-time\n");
51   rprintf(F,"     --modify-window=NUM     compare mod-times with reduced accuracy\n");
52   rprintf(F," -T, --temp-dir=DIR          create temporary files in directory DIR\n");
53   rprintf(F," -y, --fuzzy                 find similar file for basis if no dest file\n");
54@@ -463,6 +465,7 @@ static struct poptOption long_options[] 
55   {"chmod",            0,  POPT_ARG_STRING, 0, OPT_CHMOD, 0, 0 },
56   {"ignore-times",    'I', POPT_ARG_NONE,   &ignore_times, 0, 0, 0 },
57   {"size-only",        0,  POPT_ARG_NONE,   &size_only, 0, 0, 0 },
58+  {"date-only",        0,  POPT_ARG_NONE,   &date_only, 0, 0, 0 },
59   {"one-file-system", 'x', POPT_ARG_NONE,   0, 'x', 0, 0 },
60   {"update",          'u', POPT_ARG_NONE,   &update_only, 0, 0, 0 },
61   {"existing",         0,  POPT_ARG_NONE,   &ignore_non_existing, 0, 0, 0 },
62@@ -1676,6 +1679,9 @@ void server_options(char **args,int *arg
63 			args[ac++] = "--size-only";
64 	}
65 
66+	if (date_only)
67+		args[ac++] = "--date-only";
68+
69 	if (modify_window_set) {
70 		if (asprintf(&arg, "--modify-window=%d", modify_window) < 0)
71 			goto oom;
72--- old/rsync.yo
73+++ new/rsync.yo
74@@ -360,6 +360,7 @@ to the detailed description below for a 
75      --timeout=TIME          set I/O timeout in seconds
76  -I, --ignore-times          don't skip files that match size and time
77      --size-only             skip files that match in size
78+     --date-only             skip files that match in mod-time
79      --modify-window=NUM     compare mod-times with reduced accuracy
80  -T, --temp-dir=DIR          create temporary files in directory DIR
81  -y, --fuzzy                 find similar file for basis if no dest file
82@@ -477,6 +478,12 @@ regardless of timestamp. This is useful 
83 after using another mirroring system which may not preserve timestamps
84 exactly.
85 
86+dit(bf(--date-only)) Normally rsync will skip any files that are
87+already the same size and have the same modification time-stamp. With the
88+--date-only option, files will be skipped if they have the same
89+timestamp, regardless of size. This may be useful when the remote
90+files have passed through a size-changing filter, e.g. for encryption.
91+
92 dit(bf(--modify-window)) When comparing two timestamps, rsync treats the
93 timestamps as being equal if they differ by no more than the modify-window
94 value.  This is normally 0 (for an exact match), but you may find it useful
95--- old/rsync.1
96+++ new/rsync.1
97@@ -426,6 +426,7 @@ to the detailed description below for a 
98      \-\-timeout=TIME          set I/O timeout in seconds
99  \-I, \-\-ignore\-times          don\&'t skip files that match size and time
100      \-\-size\-only             skip files that match in size
101+     \-\-date\-only             skip files that match in mod-time
102      \-\-modify\-window=NUM     compare mod-times with reduced accuracy
103  \-T, \-\-temp\-dir=DIR          create temporary files in directory DIR
104  \-y, \-\-fuzzy                 find similar file for basis if no dest file
105@@ -556,6 +557,13 @@ regardless of timestamp\&. This is usefu
106 after using another mirroring system which may not preserve timestamps
107 exactly\&.
108 .IP 
109+.IP "\fB\-\-date\-only\fP"
110+Normally rsync will skip any files that are
111+already the same size and have the same modification time-stamp\&. With the
112+\-\-date\-only option, files will be skipped if they have the same
113+timestamp, regardless of size\&. This may be useful when the remote
114+files have passed through a size-changing filter, e\&.g\&. for encryption\&.
115+.IP 
116 .IP "\fB\-\-modify\-window\fP"
117 When comparing two timestamps, rsync treats the
118 timestamps as being equal if they differ by no more than the modify-window
119