Creating a New Project

To start a new project with Cargo, use cargo new:

$ cargo new hello_world --bin

We’re passing --bin because we’re making a binary program: if we were making a library, we’d leave it off. This also initializes a new git repository by default. If you don't want it to do that, pass --vcs none.

Let’s check out what Cargo has generated for us:

$ cd hello_world
$ tree .
.
├── Cargo.toml
└── src
    └── main.rs

1 directory, 2 files

If we had just used cargo new hello_world without the --bin flag, then we would have a lib.rs instead of a main.rs. For now, however, this is all we need to get started. First, let’s check out Cargo.toml:

[package]
name = "hello_world"
version = "0.1.0"
authors = ["Your Name <you@example.com>"]

This is called a manifest, and it contains all of the metadata that Cargo needs to compile your project.

Here’s what’s in src/main.rs:

fn main() {
    println!("Hello, world!");
}

Cargo generated a “hello world” for us. Let’s compile it:

$ cargo build
   Compiling hello_world v0.1.0 (file:///path/to/project/hello_world)

And then run it:

$ ./target/debug/hello_world
Hello, world!

We can also use cargo run to compile and then run it, all in one step (You won't see the Compiling line if you have not made any changes since you last compiled):

$ cargo run
   Compiling hello_world v0.1.0 (file:///path/to/project/hello_world)
     Running `target/debug/hello_world`
Hello, world!

You’ll now notice a new file, Cargo.lock. It contains information about our dependencies. Since we don’t have any yet, it’s not very interesting.

Once you’re ready for release, you can use cargo build --release to compile your files with optimizations turned on:

$ cargo build --release
   Compiling hello_world v0.1.0 (file:///path/to/project/hello_world)

cargo build --release puts the resulting binary in target/release instead of target/debug.

Compiling in debug mode is the default for development-- compilation time is shorter since the compiler doesn't do optimizations, but the code will run slower. Release mode takes longer to compile, but the code will run faster.