Copy directory structure on top of another

Question

I would like to move a directory and all its contents ontop of another.

By this I mean, that if I have two directories, A and B and I want to move B onto A, I want files and directories that are not in A but are in B to be simply copied across to A, files of the same name in A to be updated to the copies in B, and folders of the same name in A to be updated with new contents from B but otherwise have existing contents retained

Is there a way to do this easily in bash?

Incidentally, it is my understanding that this is what happens when you extract a tar archive over an older version of that archive. Is this true?

Answer 1

rsync -a -v -n /path/to/a/ /path/to/b/

If everything looks ok, remove the -n flag make it actually do the work. If you don't want it to be so chatty, remove the -v flag.

Edit: to be precise, this makes b have everything that a has, plus keep everything b had before.

Answer 2

You're on the right track with tar. This command will do what you want:

$ cd /path/to/A
$ tar -cf - * | tar -C /path/to/B -xf -

I've also seen cpio or rsync used for this purpose.

Here's an example run with tar:

/tmp $ tree A B
A
|-- one
|   `-- two
|       |-- four
|       `-- three
`-- uno
    `-- hello
B
|-- dos
|   |-- hi
|   `-- tres
`-- one
    `-- two
        `-- three

7 directories, 5 files
/tmp $ md5sum A/one/two/three B/one/two/three 
764efa883dda1e11db47671c4a3bbd9e  A/one/two/three
d41d8cd98f00b204e9800998ecf8427e  B/one/two/three
/tmp $ (cd A; tar -cf - * | tar -C ../B -xf -)
/tmp $ tree A B
A
|-- one
|   `-- two
|       |-- four
|       `-- three
`-- uno
    `-- hello
B
|-- dos
|   |-- hi
|   `-- tres
|-- one
|   `-- two
|       |-- four
|       `-- three
`-- uno
    `-- hello

8 directories, 7 files
/tmp $ md5sum A/one/two/three B/one/two/three 
764efa883dda1e11db47671c4a3bbd9e  A/one/two/three
764efa883dda1e11db47671c4a3bbd9e  B/one/two/three
/tmp $ 

Hope that helps!

Answer 3

It sounds like you want to synchronize too directories.

It does take a bit more setup, but if you want to frequently do this you may want to look at unison. Here is an article describing the setup.