docs/machine/reference/scp.md

scp

Copy files from your local host to a machine, from machine to machine, or from a machine to your local host using scp.

The notation is machinename:/path/to/files for the arguments; in the host machine's case, you don't have to specify the name, just the path.

Consider the following example:

$ cat foo.txt
cat: foo.txt: No such file or directory
$ docker-machine ssh dev pwd
/home/docker
$ docker-machine ssh dev 'echo A file created remotely! >foo.txt'
$ docker-machine scp dev:/home/docker/foo.txt .
foo.txt                                                           100%   28     0.0KB/s   00:00
$ cat foo.txt
A file created remotely!

Just like how scp has a -r flag for copying files recursively, docker-machine has a -r flag for this feature.

In the case of transferring files from machine to machine, they go through the local host's filesystem first (using scp's -3 flag).