Getting started

Hi and welcome to Crystal’s Reference Book!

First, let’s make sure to install the compiler so that we may try all the examples listed in this book.

Once installed, the Crystal compiler should be available as crystal command.

Let’s try it!

Crystal version

We may check the Crystal compiler version. If Crystal is installed correctly then we should see something like this:

  1. $ crystal --version
  2. Crystal 1.12.1 [4cea10199] (2024-04-11)
  4. LLVM: 15.0.7
  5. Default target: x86_64-unknown-linux-gnu

Great!

Crystal help

Now, if we want to list all the options given by the compiler, we may run crystal program without any arguments:

  1. $ crystal
  2. Usage: crystal [command] [switches] [program file] [--] [arguments]
  4. Command:
  5.     init                     generate a new project
  6.     build                    build an executable
  7.     docs                     generate documentation
  8.     env                      print Crystal environment information
  9.     eval                     eval code from args or standard input
  10.     play                     starts Crystal playground server
  11.     run (default)            build and run program
  12.     spec                     build and run specs (in spec directory)
  13.     tool                     run a tool
  14.     help, --help, -h         show this help
  15.     version, --version, -v   show version
  17. Run a command followed by --help to see command-specific information, ex:
  18.     crystal <command> --help

More details about using the compiler can be found on the manpage man crystal or in our compiler manual.

Hello Crystal

The following example is the classic Hello World. In Crystal it looks like this:

hello_world.cr

  1. puts "Hello World!"

We may run our example like this:

  1. $ crystal hello_world.cr
  2. Hello World!

Note

The main routine is simply the program itself. There’s no need to define a “main” function or something similar.

Next you might want to start with the Introduction Tour to get acquainted with the language.

Here we have two more examples to continue our first steps in Crystal: