By the end of this lesson
Read arguments without confusing them with source code or terminal syntax.
Before you start
- Rust 1.90.0 or later, a terminal and a plain-text editor. Examples were tested with Rust 1.90.0, Edition 2024 on Linux.
- Complete lesson 24, or be comfortable explaining and running its examples.
Three words to know
- Argument
- An input passed when starting a process.
- Exit status
- A numeric success/failure result returned to the shell.
- stderr
- The output stream normally used for diagnostics.
1. Understand the idea
The executable name is the first process argument; skip(1) moves past it. args_os preserves operating-system strings, useful for file paths that need not be valid Unicode. With Cargo, -- separates Cargo options from arguments passed to the program. Quote paths containing spaces. A returned output string and an exit status are different things.
2. Save, run and observe
Save this complete program as lesson.rs in a fresh practice folder. It replaces that lesson file only; keep earlier examples separately. Compile it with rustc, then run the executable. Rust source goes in the editor; rustc and cargo commands go in the terminal.
fn main() {
let mut args = std::env::args_os().skip(1);
match (args.next(), args.next()) {
(Some(_path), None) => println!("one argument"),
_ => { eprintln!("error: expected one path"); std::process::exit(2); }
}
}
What you should see · example output
one argument
rustc --edition=2024 lesson.rs -o lesson
./lesson tasks.tsv3. Explain the result
This example checks argument count but does not open the path. Run the executable as ./lesson tasks.tsv on Bash or .\lesson.exe tasks.tsv in PowerShell. Without the argument, it writes the generic diagnostic to stderr and exits with status 2; stdout stays empty. In Cargo use cargo run -- tasks.tsv.
YOUR TURN
A small check before you continue
Why should a file argument named my tasks.tsv be quoted?
Show a suggested answer
Without quotes, the shell can pass it as two arguments. Use "my tasks.tsv" as one argument.
Sources and scope
Documentation and examples reviewed 2026-10-18. Provider screens, package versions and output wording can differ. Examples show expected outcomes; they are not a claim that OpenViST connected to your server or verified your setup.