Rust std::process with special characters - windows

Question

I've got a very simple rust program but its not doing quite what I'd expect. Running on Windows, using a powershell prompt, I can do the following to display the path:
echo "%PATH%"
and I have a simple Rust program with:
Command::new("echo")
.arg("%PATH%")
.spawn()
.expect("ls command failed to start");
The command will launch and run, but it outputs:
%PATH%
instead of the path contents, like I'd expect. Other commands which don't use special characters seem to work as expected, so I suspect its related to handling them but I don't see a way in Rust to make the command any more primitive than it already is.
I've tried various formatting but it either fails to run the command or does the same.
I also tried using $env:path, but this always fails to run from Rust with a cannot find the path specified error.
Are there any suggestions for handling this? I could write the contents to a file and run the file instead, but running these types of commands from other languages directly works fine so I think it should work from Rust as well.
Thanks!
Update:
Managed to get the expected results from by using:
let out = Command::new("cmd")
.arg("/C")
.arg("echo %PATH%")
.spawn()
.expect("ls command failed to start");
}
I think the question got interpreted a bit differently, as getting the path was just an example of a larger issue I was seeing. Updating with the above solved my larger issue as well.

Answer 1

As the comment by French says: Spawning the process does not include the Powershell-environment, which would expand %PATH% to it's actual content before launching the process.
You need to get the content of PATH via std::env yourself or lookup the Powershell documentation on how to launch a subprocess inside a powershell-session.

Answer 2

As others have mentioned, it's not the special characters, it's the fact that those special characters are interpreted by powershell before the "echo" program runs at all.
Using https://doc.rust-lang.org/cargo/reference/environment-variables.html as a reference for how to look up environment variables, try something like this:
use std::env;
fn main() {
let cur_path = env::var("PATH").unwrap();
println!("Environment is: {}", cur_path);
}
You can try this here: https://play.rust-lang.org/
You can then feed cur_path into your "Command::new" if you wish. The trick is that powershell substitutes that argument BEFORE launching echo, which you may not have known, whereas when you execute the echo program directly, you have to do that substitution yourself.