# Chapter 3: Writing Your First Crystal Program

## Writing Your First Crystal Program  <a href="#writing-your-first-crystal-program" id="writing-your-first-crystal-program"></a>

Okay! Let’s get down to it: in order to call yourself an “X Programmer,” you must write “Hello, world” in X. So let’s do it. Open up a text file: I’ll use `vim` because I’m that kind of guy, but use whatever you want. Crystal programs end in `.cr`:

```
$ vim hello.cr
```

Put this in it:

```ruby
puts "Hello World!"
```

And run it with `crystal` command:

```
$ crystal hello.cr
Hello World!
```

It should run and print the output without error. If you get one, double check that you have the double quotation marks. Errors look like this:

```
$ crystal hello.cr
Syntax error in ./hello.cr:1: unterminated char literal, use double quotes for strings

puts 'Hello World!'
```

By the way `crystal` command is great for quickly running your code but it’s slow. Each time it compiles and runs your program Let’s see how much does it takes to run that program.

```
$ time crystal hello.cr
crystal hello.cr  0.30s user 0.20s system 154% cpu 0.326 total
```

0.326 seconds for a `Hello World`? Now that’s slow.

Instead of compiling and running again you can compile it to native code with the `build`command.

```
$ crystal build hello.cr
```

And to run your program, do the Usual UNIX Thing:

```
$ time ./hello
./hello  0.00s user 0.00s system 87% cpu 0.006 total
```

You should see “Hello, world.” print to the screen 50x faster :) Congrats!


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