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Using Command Line Arguments and Environment Variables ​

The standard library package for working with the environment is std::env.

Access the process's environment variables

rust
let env_var = std::env::var("VARIABLE");
let env_var = std::env::var("VARIABLE");

Or check the presence of an environment variable

rust
let env_var_exists: bool = env::var("VARIABLE").is_err();
let env_var_exists: bool = env::var("VARIABLE").is_err();

Method 1: Manual ​

To read arguments from the command line using Rust's standard library use the std::env::args function.

rust
use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();

    let option = &args[1];
    let flag   = &args[2];

    // -- rest of program --
}
use std::env;

fn main() {
    let args: Vec<String> = env::args().collect();

    let option = &args[1];
    let flag   = &args[2];

    // -- rest of program --
}

Note: The call to args() returns an iterator which can be converted into a collection using the .collect() method.

TODO: add section on Clap for CLI programs and then reference this in Essential Crates