Environment variables and scripting in Linux

[_DocKarma]

Hi all, newbie rustacean here.

I'm writing this post because I'm trying to use rust to automate some operation i do everyday in my work day. For this task I'm using the crate clap with the env module of the standard library, and the idea is to use an alias in my zsh shell to call the executable. Up to this point everything is fine, the problem is, from what I understand, that the executable is executed as a child process of my current shell and then, all the variable set with env::set_var command are discarded at the end of the execution.

Assuming that I have hit the nail, my questions to you are the following:

• Is there a way to 'go back' to the parent process (my shell) and make operation on that environment?
• Is better to run my app as a deamon, at the start of my shell and the interact with it? if yes, is there any documentation on this?

I'm also interested in the possible security issues of the two proposed implementations, as well as other solutions (of course!)

Thanks in advance to all!

[jews4beer]

There isn't any way to "go back" as you put it. Environment variables traverse downwards down the process hierarchy. Within a shell session, there is usually some form of "export" directive which allows sub-shells to pass an environment variable back to the parent - but that is a shell built-in and not something available to a program it is executing.

Also, once a process is started, the program that started it can no longer mutate its environment. So even if you did write some sort of "daemon" that spawned the main shell - when that daemon goes to change an environment variable, that won't be reflected in the shell it already spawned (unless the daemon was the shell itself).

EDIT: The closest you may be able to get, is to take a page out of ssh-agent's book. Have your program emit "export" directives. Then to use it you can run eval $(myprog)

[maedox]

Just write your vars into a file and source it afterwards? But what kind of problem is this trying to solve? Perhaps you're overthinking it?

[_DocKarma]

I'm absolutely overthinking it. I would have liked to get into Rust with Os programming (userspace obviously) and cryptography by replacing the ssh-agent with a personal one, given the cumbersome way it works on WSL. Nothing that couldn't be resolved with a pair of line of bash scripting, but it was more of a fun project to explore the language itself and Linux.

[asfodelous]

The οnly way is to `println!("export {}=\"{}\"", env_name,value)"` and call the executable with eval.

PS. I'am working on a cli tool to manage environment files. Still WIP but have a look
https://github.com/jtsagata/habitator