How to edit file in a docker container when no editor is installed

I recently needed to edit a file in a docker container, but when I tried editing the file, no luck:

/var/www/html/config# vi config.ini.php 
bash: vi: command not found

Of course, I tried installing an editor right away:

/var/www/html/config# apt install nano
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package nano is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'nano' has no installation candidate

or

/var/www/html/config# apt install vi
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package vi

or

/var/www/html/config# apt install vim
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package vim

So, nothing worked. I wasn't too keen on the idea of mapping the config file I needed to edit to my docker host either, so I found another solution:

docker cp name-app:/var/www/html/config/config.ini.php .
Successfully copied 6.66kB to /data/dockers/dir/.

What this does is that it copies the file from the docker container directly to the docker host. Now I had the file on my docker host where I was able to edit it with my favourite editor (nano). Once I was done, the same logic applied:

docker cp config.ini.php name-app:/var/www/html/config/config.ini.php
Successfully copied 6.66kB to name-app:/var/www/html/config/config.ini.php

And that's it. Just to test that my docker container retained the config, I restarted it and all was good! This will of course depend on the docker container itself, but in my case, it worked like a charm!