I believe you can use rsync
to do this. The key observation would be in needing to use the --existing
and --update
switches.
--existing skip creating new files on receiver
-u, --update skip files that are newer on the receiver
A command like this would do it:
$ rsync -avz --update --existing src/ dst
Example
Say we have the following sample data.
$ mkdir -p src/; touch src/file{1..3}
$ mkdir -p dst/; touch dst/file{2..3}
$ touch -d 20120101 src/file2
Which looks as follows:
$ ls -l src/ dst/
dst/:
total 0
-rw-rw-r--. 1 saml saml 0 Feb 27 01:00 file2
-rw-rw-r--. 1 saml saml 0 Feb 27 01:00 file3
src/:
total 0
-rw-rw-r--. 1 saml saml 0 Feb 27 01:00 file1
-rw-rw-r--. 1 saml saml 0 Jan 1 2012 file2
-rw-rw-r--. 1 saml saml 0 Feb 27 01:00 file3
Now if I were to sync these directories nothing would happen:
$ rsync -avz --update --existing src/ dst
sending incremental file list
sent 12 bytes received 31 bytes 406.00 bytes/sec
total size is 0 speedup is 0.00
If we touch
a source file so that it's newer:
$ touch src/file3
$ ls -l src/file3
-rw-rw-r--. 1 saml saml 0 Feb 27 01:04 src/file3
Another run of the rsync
command:
$ rsync -avz --update --existing src/ dst
sending incremental file list
file3
sent 115 bytes received 31 bytes 292.00 bytes/sec
total size is 0 speedup is 0.00
We can see that file3
, since it's newer, and that it exists in dst/
, it gets sent.
Testing
To make sure things work before you cut the command loose, I'd suggest using another of rsync
's switches, --dry-run
. Let's add another -v
too so rsync
's output is more verbose.
$ rsync -avvz --dry-run --update --existing src/ dst
sending incremental file list
delta-transmission disabled for local transfer or --whole-file
file1
file2 is uptodate
file3 is newer
total: matches=0 hash_hits=0 false_alarms=0 data=0
sent 88 bytes received 21 bytes 218.00 bytes/sec
total size is 0 speedup is 0.00 (DRY RUN)