I think you cannot use ~/.ssh/config to solve your problem because this file is for ssh, not for scp. It's true scp uses ssh under the hood, but -O you want to force is an option strictly for scp, not for ssh.
You may be able to achieve an acceptable result with a wrapper script. This is the script:
#!/bin/sh
exec /usual/path/to/scp -O "$@"
You need to use the full path to the real scp. Save the script as scp in a directory that is earlier in your $PATH than all other directories in $PATH that hold other (in practice: the real) scp executable(s). Create a new directory and adjust your $PATH if needed. Make the script executable (chmod +x scp).
From now on any process that inherits your modified $PATH and tries to run scp will run the wrapper instead of the real scp. The wrapper will replace itself with the real scp that will get -O along with all arguments passed to the wrapper. This way -O will be injected automatically.
There are cases when the method cannot work:
If a process calling scp uses $PATH which is not your modified $PATH then it won't find the wrapper and it will run the real scp directly; so -O won't be injected. For this reason you may want to modify $PATH as "globally" as possible.
If a process calls /usual/path/to/scp explicitly then it will obviously call the real scp directly regardless of $PATH; so -O won't be injected.
A way to overcome these is:
- Do not modify
$PATH.
- Move the original
scp to a different pathname.
- Use this pathname in the wrapper, so the wrapper execs to the real
scp as it always should.
- Save the wrapper as
/usual/path/to/scp.
The downside is your OS, when being upgraded, may replace the wrapper with a new version of the real scp. This mishap cannot happen in the method with modified $PATH and unaltered /usual/path/to/scp.
