Hi and welcome to Crystal's Reference Book!
First let's make sure to install the compiler correctly 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 0.34.0 (2020-04-07) LLVM: 10.0.0 Default target: x86_64-apple-macosx
Now, if we want to list all the options given by the compiler, we may run
crystal program without any arguments:
$ crystal Usage: crystal [command] [switches] [program file] [--] [arguments] Command: 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:
# hello_world.cr puts "Hello World!"
We may run our example like this:
$ crystal hello_world.cr Hello World!
The main routine is simply the program itself. There's no need to define a "main" function or something similar.
Here we have two more examples to continue our first steps in Crystal: