Sometimes I have two trees that used to have the same content, but have grown out of sync (because I moved disks around or whatever). A good example is a tree where I mirror upstream packages from Fedora.

I want to merge those two trees again by moving all of the files from tree1 into tree2.

Usually I do this with:

rsync -arv tree1/* tree2

Then delete tree1.

However, this takes an awful lot of time and disk space, and it would be much easier to be able to do:

mv -r tree1/* tree2

In other words, a recursive move. It would be faster because first of all it would not even copy, just move the inodes, and second I wouldn't need a delete at the end.

Does this exist ?

As a test case, consider the following sequence of commands:

$ mkdir -p a/b
$ touch a/b/c1
$ rsync -arv a/ a2
sending incremental file list
created directory
./
b/
b/c1
b/c2

sent 173 bytes  received 57 bytes  460.00 bytes/sec
total size is 0  speedup is 0.00
$ touch a/b/c2

What command would now have the effect of moving a/b/c2 to a2/b/c2 and then deleting the a subtree (since everything in it is already in the destination tree) ?