How to affect a parent process environment in Linux?-CodePudding

I know that a child process cannot directly affect its parent process, HOWEVER, how does a tool like nvm work? It's a CLI tool that can "instantly" switch between nodejs versions, which I think means modifying the PATH somehow to point to a different binary installed on your PC.

By "instantly" I mean that you can open a shell, run nvm use [version], and the version is available to use in the same shell. How can a script change the PATH of the shell it's run on?

I've been trying to follow the source code but I'm stumped

CodePudding user response：

$ type nvm
nvm is a shell function from /home/jkugelman/.nvm/nvm.sh

A script runs in a child process and cannot change environment variables in the parent. A shell function, on the other hand, runs in the same shell and can manipulate the environment.

If you want to see exactly what it's doing use declare -pf (print function) or which:

$ declare -pf nvm
nvm () {
    # code snipped
}

CodePudding user response：

The command is likely a function. For example:

#!/bin/bash

function set_nvm() {
        PATH="$1:$PATH"
}

Source the above file so that the function is available in the shell. This can be done in your .bashrc so you don't have to manually do it every time:

$ . test.sh

Then you can call the function as it were a command:

$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin
$ set_nvm /tmp
$ echo $PATH
/tmp:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin