For years, I have used scp to transfer files between Unix/Linux machines. I noted quite a while ago that having an echo statement in my login script (in this case .bashrc) caused the file transfer to fail, so I removed all echo statements from login scripts, using them only for temporary debugging. Today, I believe I have found the way to have my cake (use scp to copy files) and eat it too (leave the echo statements in the login script).
If your .bashrc looks like this:
#!/bin/bash echo "Running the .bashrc file" # correct spelling mistakes shopt -s cdspell # save multiline commands in the command history shopt -s cmdhist # some useful aliases alias c='clear' alias ls='ls -p' alias vi='vim' echo "done with .bashrc file"
And you connect via SSH, you’ll see the following:
[me@otherhost]$ ssh myhost me@myhosts's password: Running the .bashrc file done with .bashrc file [me@myhost me]$
Which is fine for an SSH session. In fact, you might even ask questions of logging in users, or dump an entire warning banner to the screen to indemnify you for legal reasons. Many interactive possibilities exist.
Now say you wish to copy a file from one server to another:
[me@otherhost]$ scp myfile myhost:~/ Running the .bashrc file
Once this is done, you only see the output from the first echo. What’s worse, the copy never happens. Some claim this is a bug. The fact that the bug was reported in 2000 and still exists in scp indicates to me that the scp authors don’t consider it a problem.
The solution is in testing for the existence of a terminal:
#!/bin/bash if tty > /dev/null 2>&1; then echo "Running the .bashrc file" fi # correct spelling mistakes shopt -s cdspell # save multiline commands in the command history shopt -s cmdhist # some useful aliases alias c='clear' alias ls='ls -p' alias vi='vim' if tty > /dev/null 2>&1; then echo "done with .bashrc file" fi
Now scp will work without any output to the screen. More importantly, your files will be copied:
[me@otherhost]$ scp myfile myhost:~/ me@myhost's password: myfile 100% 1896KB 1.9MB/s 00:00
Thanks to the forums on Ars Technica for leading me to the answer to this issue. As that post existed in 2000, I now see why the openssh folks haven’t “fixed” scp.