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
Let's try it!
We may check the Crystal compiler version. If Crystal is installed correctly then we should see something like this:
$ crystal --version
Crystal 1.11.2 [fda656c71] (2024-01-18)
Default target: x86_64-unknown-linux-gnu
Now, if we want to list all the options given by the compiler, we may run
crystal program without any arguments:
Usage: crystal [command] [switches] [program file] [--] [arguments]
init generate a new project
build build an executable
docs generate documentation
env print Crystal environment information
eval eval code from args or standard input
play starts Crystal playground server
run (default) build and run program
spec build and run specs (in spec directory)
tool run a tool
help, --help, -h show this help
version, --version, -v show version
Run a command followed by --help to see command-specific information, ex:
crystal <command> --help
More details about using the compiler can be found on the manpage
man crystal or in our compiler manual.
The following example is the classic Hello World. In Crystal it looks like this:
puts "Hello World!"
We may run our example like this:
$ crystal hello_world.cr
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: