Allow specifying target binary via cli

[asdil12]

When changing the setting of a binary, currently only the priority can be specified.
It would be better to allow specifying the target binary - at least additionally.
eg:

alts -n flask -b /usr/bin/foo

This would also allow specifying a target binary that is not actually an alternative announced by a package.

[AdamMajer]

This would break the basic assumption of libalternatives which is that the defaults are provided by packages at install time. The purpose of libalternatives is then to switch between these pre-installed alternatives. You should then never up up with situation like error: No such file or directory that could happen with update-alternatives when you rollback to previous installation after an update.

So I would say this is out-of-scope.

The best way is to add the alternative to the package. It's just a simple text file. For example for one alternative for /usr/bin/node,

> cat /usr/share/libalternatives/node/12.conf
binary=/usr/bin/node12
man=node12.1

Or you can hack it locally by adding this type of file into the filesystem. This will break if you ever uninstall the package providing this binary, but it would be similar by hardcoding the binary.

[asdil12]

At least we could cover the use case of allowing to specify the target by alternatively passing the binary instead of the prio, which allows user readable commands.
Then alts can still (when storing the updated override) internally lookup the candidate with the matching binary entry and store the configuration using the priority.

[AdamMajer]

Thanks for clarification. Basically, instead of doing

alts -n node -p 12

allow for

alts -n node -b /usr/bin/node12

and it would be equivalent result.