1. Maintain a directory of shim binaries with the same name as every Ruby binary (ruby, irb, rake, gem, etc).
2. Put the shim directory at the front of your $PATH.
3. When a shim is run (as in typing `rake` from the command line or running a script with a `#!/usr/bin/env ruby` shebang), check for a version file in the current directory or any parent directory, map that to the right path, and re-exec the corresponding binary.
Doesn't this solution not scale? Doesn't this mean a shim must be created for every gem that I install that has a binary? Or is this only required for "core" binaries?
`ls -l /usr/bin | wc -l` reports 1085 entries on my machine. Meanwhile, I have 40 entries in my ~/.rbenv/shims directory. I think the shell can handle it.
I'm sorry, I was not aware of the 'rehash' function, I thought rbenv would have to ship with all the required shims. The rehash functionality is quite clever and cool. Is there an easy way to have that automatically execute after I do any installation of a ruby or gem?
Couldn't you also use $PROMPT_COMMAND? This gets executed right before showing the prompt, so cwd would already have been called and it would be much easier to chain.
Of course you'd run more often than when hooking cd, but just checking for a new .rvmrc isn't so expensive.
The problem would probably be that you wouldn't get called from within scripts (there is no prompt there), but that could also be an advantage because it would ensure that a scripts cd would continue to work "headless".
I'd have to look into this and really see what rvm actually needs the hook for. As such I'm just thinking loudly at the moment.
