Preserve the order of PATH locations when changing node versions

[zeorin]

nvm may not be the only utility managing the PATH. The order of locations in the PATH matters, as executables in locations in the beginning of PATH will be shadowing executables that are in later locations.

An example of this is when the output of $(npm bin) is prepended to the PATH. If nvm is used to change the node version after that, it should not change the order of path locations.

It's up to the user to change the PATH in a way that they prefer, by loading utilities in the correct order.

[ljharb]

I don't necessarily agree with the claim that the user should be solely managing their PATH - by using nvm, the user is explicitly ceding control of their PATH to it.

[ljharb]

I've tried to avoid using expr in nvm because of https://github.com/koalaman/shellcheck/wiki/SC2003. Can this be written differently?

[zeorin]

From that link:

sh doesn't have a great replacement for the : operator (regex match). ShellCheck tries not to warn when using expr with :

I'm not aware of another way to do this and still keep POSIX compatibility.

[ljharb]

Could it use awk or sed?

[zeorin]

How about using grep?

[ljharb]

Sure, any posix tool is great.

[zeorin]

Done 😁

[zeorin]

I'm not saying that the user is solely managing their path. Simply that it's up to the user to load their PATH-adapting utilities in an order that makes sense for them.

In the current scenario, nvm is actively hostile to any other PATH-changing utility or script.

nvm's core purpose is not to manage the PATH. Managing the PATH is how nvm achieves its ends, but it's not its raison d'être. It's not a PATH manager. It's a Node manager. The PATH management is incidental.

Whilst I accept, as a user of nvm, that it can't manage my node versions and still provide a good user experience without changing PATH, I find it a stretch to say that a user is explicitly ceding control of their PATH completely to NVM. I'd say it's more implicit, if the user even has any idea at all of what's happening in the first place (the amount of *nix noobs is growing—nothing wrong with that, but what you're saying may not be obvious to them).

In the current scenario:

• When NVM is sourced, or does almost anything, it's at the front of the PATH and dominates it.
  • Drawbacks: not sensitive to the other, non-nvm needs the PATH must serve
  • Benefits: 100% certain that the current version of node's global cli executables shadow everything else (though that's not always what we want—it's certainly not what I want: I only want it to shadow the system node's global cli executables)

In my fix:

• When NVM is sourced, or does almost anything, it's at the front of the PATH the 1st time and keeps its place the rest of the time.
  • Drawbacks: something that is relying on NVM clobbering the PATH order may no longer work (honestly, what would be counting on clobbering behaviour?); a user might find a surprising behaviour once and have to think for 5 minutes about the order of their PATH
  • Benefits: NVM can play nice with other PATH-managing utilities. It can be integrated with more tools and workflows because it's not hostile to them by default. It's sensitive, considerate. It's more useful.

In short, my argument is that the PATH doesn't serve only NVM. It serves other needs, too. Always has, always will. For NVM to assume that its needs and demands on the PATH trump the rest of the system's needs, always, no-questions-asked, no-prisoners-taken, is hostile to other tools. Tools that the user has chosen to run. I.e. that assumption is ultimately hostile to the user.

Unix has always been about giving people the freedom to do stupid things. Because without it you don't have the freedom to do clever things.

[ljharb]

@zeorin let's give this one another shot - can you rebase it on latest master, and/or check the "allow edits" checkbox on the right hand column?

[zeorin]

@ljharb I rebased the pull request branch on master.

[ljharb]

The more I try this out locally the more I'm convinced this is an excellent change.

Thanks for bearing with me!