std::process::Command can't echo environment variables

[vervaekejonathan]

I tried this code:

use std::process::Command;
...
    let s = Command::new("echo")
        .arg("$123")
        .output()
        .expect("command failed");
    println!("{}", String::from_utf8_lossy(&s.stdout));

I expected to see this happen:
Print the content of the $123 environment variable

Instead, this happened:
It literally prints $123

Meta

rustc --version --verbose:

rustc --version --verbose
rustc 1.61.0-nightly (63b8f01bb 2022-03-24)
binary: rustc
commit-hash: 63b8f01bb5ca277e7df8d7efe094ed4244c1790c
commit-date: 2022-03-24
host: x86_64-unknown-linux-gnu
release: 1.61.0-nightly
LLVM version: 14.0.0

[crumblingstatue]

It is the shell that resolves environment variables. You're not using a shell here, just directly executing a command. This is behaving as expected.

[jfrimmel]

Indeed, this is the expected behavior. This can be circumvented by actually using a shell, e.g. on POSIX:

Command::new("sh").arg("-c").arg("echo $123").output().unwrap();

[wwylele]

I did a quick check on the doc for arg

Note that the argument is not passed through a shell, but given literally to the program. This means that shell syntax like quotes, escaped characters, word splitting, glob patterns, substitution, etc. have no effect.

I guess we can expand "substitution" into "variable substitution" to make it more clear.

[Milo123459]

so is this just a documentation change?

@rustbot claim