SUPER TL;DR: fix doesn't work!
TL;DR: see fix at end!
As I chug through daily work, I realize that one serious time-saver for me would be the ability to use a shell command to open a file in DrRacket. So, for instance, I'm in a particular directory in the shell, and I want to send the text.rkt file to be opened by the already-running DrR instance. This has a vaguely quickscript flavor to it, but I think that doing it from the shell probably involves some
... well, let me go read the man page.
Okay, I'm back from the man page for open, and I'm amused by a bunch of things; it explicitly says "This behavior was also present in Tiger.". Also, it was last updated in 2017, I believe. The important piece, though, is that reading this makes it clear that the intended behavior is that if the application is already open, no new instance of the application is created. Unfortunately, the behavior I observe (I hope I'm not alone in this?
... (uh oh) ...
... does a bunch of experimentation ...
Oh! It turns out that open does exactly what I want, as long as the version DrRacket that's running matches the "default application" setting in the OS. You can change this by opening a finder window with a .rkt file, right-clicking the file, and choosing "Open With ... > Other", then finding the correct DrRacket application in the resulting Finder window and selecting the "Always Open With" checkbox before confirming your choice. For me, this causes the open command in the terminal to send the file to the running DrRacket instance to be opened, and means that (for instance) opening a whole bunch of files ...
... gah! ...
ugh ugh ugh it turns out that this literally only changes the mapping for THIS ONE FILE. There's another mechanism, the Get Info box, which allows you to set an application for all files with a given extension, and actually gives you a "this is about to change the settings for all files" warning... but it still doesn't work! My guess is that this could successfully change the mapping from one application to a totally different one, but when you have multiple versions of a single application, it doesn't seem to change anything, which you can see immediately after confirming on that dialog, because the setting in the get info box goes right back (for me) to "8.14 (default)". Ugh.
Okay so this went from amazing success to miserable failure.
There's a great article from eclectic light on this:
... but unfortunately, it doesn't give any suggestions for directly manipulating the launch services database, just rebuilding it.