Invalid environment variable names for Command are not rejected

[dylni]

I tried this code:

use std::process::Command;

fn main() {
    println!(
        "{:?}",
        Command::new("printenv")
            .arg("foo")
            .env("foo=bar", "baz")
            .output()
    );
}

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=f3e035599c38c2bea88c8331a0b94da1

I expected to see this happen: an error that the environment variable name contains =

Instead, this happened:

Ok(Output { status: ExitStatus(unix_wait_status(0)), stdout: "bar=baz\n", stderr: "" })

There was a PR for to give errors for these variables, but it was closed due to inactivity: #39338

Meta

rustc --version:

rustc 1.63.0 (4b91a6ea7 2022-08-08)

[chenyukang]

Is there any standard explain why we need to reject = in environment variable names?

I tried in local, seems Bash accept it:

cat@LAPTOP-V6U0QKD4:~/code/rust$ foo=bar=baz printenv foo
bar=baz

I think the behavior is different between OS or shell?

[dylni]

@chenyukang The current behavior is unexpected because .env("foo=bar", "baz") will not set an environment variable called foo=bar. It will set a variable called foo.

For example, this call will fail because foo=bar is not a valid variable name:

env::set_var("foo=bar", "baz");

Since the name and value not differentiated in shells, it would not make sense to reject the assignment. However, the equivalent in Rust would be env("foo", "bar=baz").

[RodBurman]

I tried the following in /bin/zsh and also /bin/sh

% export "foo=bar"=baz
% printenv foo=bar    
baz

So you can have an environmental variable called foo=bar (at least in macOS) and so Command is correct I believe.
However the following code does not work:

fn main() {
    std::env::set_var("\"foo=bar\"", "baz");
 }

It compiles but running it fails with:

thread 'main' panicked at /Users/rod/.rustup/toolchains/stable-aarch64-apple
darwin/lib/rustlib/src/rust/library/std/src/env.rs:364:9:
failed to set environment variable `"\"foo=bar\""` to `"baz"`: Invalid argument (os error 22)
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

If the extra quotes are removed (so "foo1=bar1") it fails similarly as do single quotes ("'foo=bar'") or using an OsStr (OsStr::new"\"foo=bar\""). I am not sure the environmental variable foo=bar can be set from using std::env::set_env() unlike using export.