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Get started with Mojo🔥

On this page, we'll show you how to create the classic "Hello world" starter program with Mojo. If you'd rather read how to write Mojo code, see the introduction to Mojo.

By installing Mojo, you understand and agree to our software license.

1. Create a new project​

To create a new Mojo project, we'll use Magic—a virtual environment manager and package manager based on conda.

  1. Install Magic on macOS or Ubuntu Linux with this command:

    curl -ssL https://magic.modular.com/ | bash
    curl -ssL https://magic.modular.com/ | bash

    Then run the source command printed in your terminal.

  2. Create a Mojo project called "hello-world":

    magic init hello-world --format mojoproject
    magic init hello-world --format mojoproject

    This creates a directory named hello-world and installs the Mojo project dependencies—the only dependency for a Mojo project is the max package (Mojo is bundled with MAX).

  3. Start a shell in the project virtual environment:

    cd hello-world && magic shell
    cd hello-world && magic shell

That's it! The magic shell command activates the virtual environment so you can now start using Mojo. For example, you can check your Mojo version like this:

mojo --version
mojo --version

2. Run code in the REPL​

First, let's use the Mojo REPL, which allows you to write and run Mojo code in a command prompt:

  1. To start a REPL session, type mojo and press Enter.

  2. Type print("Hello, world!") and press Enter twice (a blank line is required to indicate the end of an expression).

    The result looks like this:

    $ mojo
    Welcome to Mojo! 🔥

    Expressions are delimited by a blank line.
    Type `:quit` to exit the REPL and `:mojo help repl` for further assistance.

      1> print("Hello world")
    Hello world
    $ mojo
    Welcome to Mojo! 🔥

    Expressions are delimited by a blank line.
    Type `:quit` to exit the REPL and `:mojo help repl` for further assistance.

      1> print("Hello world")
    Hello world

  3. To exit REPL, type :quit and press Enter, or press Ctrl + D.

You can write as much code as you want in the REPL. You can press Enter to start a new line and continue writing code, and when you want Mojo to evaluate the code, press Enter twice. If there's something to print, Mojo prints it and then returns the prompt to you.

The REPL is primarily useful for short experiments because the code isn't saved. So when you want to write a real program, you need to write the code in a .mojo source file.

3. Run a Mojo file​

Now let's write the code in a Mojo source file and run it with the mojo command:

  1. Create a file named hello.mojo (or hello.🔥) and add the following code:

    fn main():
        print("Hello, world!")
    fn main():
        print("Hello, world!")

    That's all you need. Save the file and return to your terminal.

  2. Now run it with the mojo command:

    mojo hello.mojo
    mojo hello.mojo
    Hello, world!
    Hello, world!

4. Build an executable binary​

Finally, let's build and run that same code as an executable:

  1. Create an executable file with the build command:

    mojo build hello.mojo
    mojo build hello.mojo

    The executable file uses the same name as the .mojo file, but you can change that with the -o option.

  2. Then run the executable:

    ./hello
    ./hello
    Hello, world!
    Hello, world!

The build command creates a statically compiled binary file, so it contains all the code and libraries it needs to run.

You can now deactivate the virtual environment by just typing exit:

exit
exit

Now let's try running an existing code example.

5. Run an example from GitHub​

Our Mojo code examples in GitHub include a Magic configuration file so you can simply clone the repo and run the code with magic. For example:

  1. Clone the Mojo repo:

    git clone https://github.com/modularml/mojo.git
    git clone https://github.com/modularml/mojo.git

    Only if you installed the nightly build, also checkout the nightly branch:

    git checkout nightly
    git checkout nightly

  2. Navigate to the examples:

    cd mojo/examples
    cd mojo/examples

  3. Run some code:

    magic run mojo hello_interop.mojo
    magic run mojo hello_interop.mojo
    Hello Mojo 🔥!
    9
    6
    3
    Hello from Python!
    I can even print a numpy array:  [1 2 3]
    Hello Mojo 🔥!
    9
    6
    3
    Hello from Python!
    I can even print a numpy array:  [1 2 3]

6. Install our VS Code extension (optional)​

To provide a first-class developer experience with features like code completion, quick fixes, and hover help, we've created a Mojo extension for Visual Studio Code.

Update Mojo​

To update the Mojo version in your project, use magic add and specify the max package version.

For example, if you want to always use the latest version of Mojo, you can use the * wildcard as the version and then simply run magic update (you must run magic add within the project path):

cd hello-world
cd hello-world
magic add max
magic add max
magic update
magic update

To be more specific with your package version, you can use any of the Python package version specifiers. For example:

magic add "max~=24.4"
magic add "max~=24.4"
magic add "max>=24.4,<24.5"
magic add "max>=24.4,<24.5"

Next steps​

If you have issues during install, check our known issues.

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