how to maintain multiple active versions of a port (e.g. octave)?

[Ray Zimmerman]

On Sep 23, 2016, at 10:09 AM, Ryan Schmidt <ryandesign at macports.org> wrote:
> 
>> On Sep 23, 2016, at 09:04, Ray Zimmerman <rz10 at cornell.edu> wrote:
>> 
>>> To build a previous version of a port:
>>> 
>>> https://trac.macports.org/wiki/howto/InstallingOlderPort
>>> 
>>> You can have multiple versions of a port installed at the same time, but only one active and usable at a time. You can switch between them by activating whichever one you want at the moment, but this may have consequences for any other installed ports that depend on the port whose version you're switching.
>> 
>> Ok, this sounds like something I could make use of now. I’m not familiar with the details of what activating a port does. Is it simply a matter of what get’s put in your executable path, or is there more to it?
> 
> An installed port is a compressed tarball of files. Activating a port extracts that tarball into /opt/local. 
> 
>> I guess my real question is, can I create a few symlinks to be able to execute a deactivated octave port without activating it? If so, that may be good enough for my purposes.
> 
> No, when a port is not active, the files you propose to symlink against do not exist. 

I was able to successfully build and install an older version of octave using the instructions from https://trac.macports.org/wiki/howto/InstallingOlderPort. I have the current version installed as well and can switch between the active versions with no trouble.

One last question … can you give me a quick idea of how much work would be involved in me attempting to locally implement the first approach you mentioned (different ports for different versions of octave). That is, starting with the files for the 3.8.2 revision of the octave port, what would be involved in creating a local octave38 port that could be installed simultaneously with the regular, current octave port? Am I crazy to attempt this?

   Ray