rustc main.rs: compile and run a single Rust file without Cargo

rustc main.rs compiles one Rust source file into an executable named after it (main, or main.exe on Windows) in the current directory; run it with ./main. It is the quickest way to try a snippet without creating a Cargo project. Add --edition 2024 to use the current edition (the default is 2015) and -O for an optimized build.

Compile and run

cat > main.rs <<'EOF'
fn main() {
    let args: Vec<String> = std::env::args().skip(1).collect();
    let name = args.first().map(String::as_str).unwrap_or("world");
    let total: u64 = (1..=10).sum();
    println!("hello, {name}! sum 1..=10 = {total}");
}
EOF
rustc --edition 2024 main.rs
./main
./main rustc
rustc --edition 2024 -O -o fast main.rs && ./fast optimized

hello, world! sum 1..=10 = 55
hello, rustc! sum 1..=10 = 55
hello, optimized! sum 1..=10 = 55

-o fast picks the output name. On Windows rustc also writes a .pdb debug-information file next to the .exe.

Common options

Errors and warnings

rustc stops on the first stage that fails and prints errors with a code, the file, line and column, and a hint:

cat > bad.rs <<'EOF'
fn main() {
    let count: i32 = "3";
    println!("{count}");
}
EOF
rustc --edition 2024 bad.rs

error[E0308]: mismatched types
 --> bad.rs:2:22
  |
2 |     let count: i32 = "3";
  |                ---   ^^^ expected `i32`, found `&str`
  |                |
  |                expected due to this

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.

The code in brackets (here E0308) can be looked up with rustc --explain. Warnings, such as unused variables, do not stop the build; -D warnings turns them into errors.

rustc or cargo?

Use rustc for single-file experiments, teaching and quick checks. Use Cargo as soon as you need dependencies, several files with tests, or a reproducible build: cargo new creates the project, cargo run compiles and runs it, and cargo build --release is the optimized build. Cargo calls rustc for you with the right flags, edition and dependency paths.

Pitfalls

• Old edition by default. Without --edition, code that uses async fn, dyn rules or other later syntax may fail to compile or warn. Pass the edition explicitly.
• Debug builds are slow and panic on integer overflow; release builds wrap around instead. Measure performance only with -O.
• ./main not found on Windows cmd. In cmd.exe or PowerShell, run main.exe or .\main.exe; ./main is the Unix and Git Bash spelling.
• Linker errors (linker 'cc' not found on Linux, link.exe not found on Windows) mean the system linker is missing, not a problem in your code: install the platform's C build tools.

Confirm it worked

The executable exists next to the source and runs. rustc --version shows which compiler built it.

FAQ