如何与非标准端口和两因素2FA认证进行rsync？

Question

I need to rsync to a remote server using a non-standard SSH port and 2FA which I use via Authy app. The SSH works with this command:

ssh -2 -p 9999 -i /Users/Me/.ssh/id_rsa  user@9.9.9.9 

This brings up a "Verification Code" prompt in the shell. Which I enter from Authy, and I'm in.

Given the discussion on this a StackOverflow answers I tried this variation of rsync:

rsync -rvz -e 'ssh -p 9999 -i /Users/Me/.ssh/id_rsa \
   --progress    /src/   user@9.9.9.9.9:/dest/

(Put here on two lines just for legibility, it's one line in my shell command).

This does bring up the Verification Code prompt, which I enter correctly, but then it produces this error:

protocol version mismatch -- is your shell clean?
(see the rsync man page for an explanation)
rsync error: protocol incompatibility (code 2) at compat.c(185) [sender=3.1.3]

How can I use rsync with 2FA? Many thanks.

Answer 1

Because @JGK mentioned the answer in the comment, adding answer here for posterity. This "is your shell clean" stuff is shown when remote server is echoing some output upon login, which in my case .bashrc indeed was. I've added a conditional to that echo only to apply when the shell login is "interactive", as mentioned in this Server Fault thread , and it works. Just for easier clarity, the IF condition reads as follows:

if echo "$-" | grep i > /dev/null; then
  [any code that outputs text here]
fi

Many thanks.