Hello World in Erlang

Welcome to the Hello World in Erlang page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

-module(hello_world).
-export([main/1]).

main(_) ->
   io:format("Hello, World!~n").

Hello World in Erlang was written by:

• Jeremy Grifski
• Nick Keers
• rzuckerm

This article was written by:

• Nick Keers
• rzuckerm

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

Erlang looks scary when you first look at it, so we'll show the full program and then we'll break it down into parts to fully describe it.

Breaking it down

The first key part of an Erlang program is the -module(). preprocessor directive:

-module(hello_world).

Every Erlang file must start with this directive or you'll get a compiler error like the following:

file.erl:2: no module definition

Next, to use functions from the module we've written we have to export them explicitly.

-export([main/1]).

This exports our main function, it takes one argument so we reference the function as main/1. The number of arguments is called the "arity" of the function.

Functions in Erlang start with an atom (for now, think of these as just lowercase letters + underscores), then the parameters, followed by an arrow ->. The following functions are both valid:

my_function() ->
  ok.

myfunction() ->
  ok.

Our main function only does one thing for this simple program, it calls the format function from the io module to print characters to standard output by default. io:format(). The string "Hello world!~n" includes the newline control sequence ~n - you can see a list of control sequences available for use in the documentation for io:fwrite here (scroll down to "Available control sequences").

How to Run the Solution

To run this example, just run escript hello_world.erl.