How to scp back to local when I’ve already sshed into remote machine?

Often I face this situation: I sshed into a remote server and ran some programs, and I want to copy their output files back to my local machine. What I do is remember the file path on remote machine, exit the connection, then scp user@remote:filepath .

Obviously this is not optimal. What I’m looking for is a way to let me scp file back to local machine without exiting the connection. I did some searching, almost all results are telling me how to do scp from my local machine, which I already know.

Is this possible? Better still, is it possible without needing to know the IP address of my local machine?

Answer

Given that you have an sshd running on your local machine, it’s possible and you don’t need to know your outgoing IP address. If SSH port forwarding is enabled, you can open a secure tunnel even when you already have an ssh connection opened, and without terminating it.

Assume you have an ssh connection to some server:

local $ ssh [e-mail]
Password:
remote $ echo abc > abc.txt  # now we have a file here

OK now we need to copy that file back to our local server, and for some reason we don’t want to open a new connection. OK, let’s get the ssh command line by pressing Enter ~C (Enter, then tilde, then capital C):

ssh> help
Commands:
      -L[bind_address:]port:host:hostport    Request local forward
      -R[bind_address:]port:host:hostport    Request remote forward
      -D[bind_address:]port                  Request dynamic forward
      -KR[bind_address:]port                 Cancel remote forward

That’s just like the regular -L/R/D options. We’ll need -R, so we hit Enter ~C again and type:

ssh> -R 127.0.0.1:2222:127.0.0.1:22
Forwarding port.

Here we forward remote server’s port 2222 to local machine’s port 22 (and here is where you need the local SSH server to be started on port 22; if it’s listening on some other port, use it instead of 22).

Now just run scp on a remote server and copy our file to remote server’s port 2222 which is mapped to our local machine’s port 22 (where our local sshd is running).

remote $ scp -P2222 abc.txt user@127.0.0.1:
user@127.0.0.1's password:
abc.txt                   100%    4     0.0KB/s   00:00

We are done!

remote $ exit
logout
Connection to example.com closed.
local $ cat abc.txt
abc

Tricky, but if you really cannot just run scp from another terminal, could help.