An environment variable is a named operating-system or process setting stored as a string key and string value. Programs use these values for overall configuration rather than for arguments typed on the command line. section 18.2.3 section 18.5
In Rust, the standard library lets a program inspect and change these settings:
- Read one value with std::env::var("RUST_BACKTRACE"); an unset variable produces Err(NotPresent). section 14.2.2
- List all variables with std::env::vars(), which yields (String, String) key-value pairs. section 18.2.3
- Set a value while the program runs with std::env::set_var("RUST_BACKTRACE", "1"). section 14.2.2
- Use configuration fallbacks: check RUST_LOG first, then choose a logging level from LOGGER_URL when needed. section 18.2.3
fn main() {
for (key, value) in std::env::vars() {
println!("{key}: {value}");
}
}
The listing makes the key-value shape visible by printing every environment variable available to a Rust process. section 18.2.3
