Hello World!

A "Hello World" program is a computer program which prints out "Hello, world!" on a display device. It is used in many introductory tutorials for teaching a programming language. Such a program is typically one of the simplest programs possible in a computer language. Some are surprisingly complex, especially in some graphical user interface (GUI) contexts, but most are very simple, especially those which rely heavily on a particular command line interpreter ("shell") to perform the actual output. In an embedded system, the text may be sent to a liquid crystal display (LCD), or the message may be substituted by some other appropriate signal, such as a LED being turned on.

Purpose
A "hello world" program has become the traditional first program that many people learn. In general, it is simple enough that people who have no previous experience with computer programming can easily understand it, especially with the guidance of a teacher or a written guide. Using this simple program as a basis, computer science principles or elements of a specific programming language can be explained to novice programmers. Experienced programmers learning new languages can also gain a lot of information about a given language's syntax and structure from a hello world program.

In addition, hello world can be a useful sanity test to make sure that a language's compiler, development environment, and run-time environment are correctly installed. Configuring a complete programming toolchain from scratch to the point where even trivial programs can be compiled and run can involve substantial amounts of work. For this reason, a simple program is used first when testing a new tool chain.

"Hello world" is also used by computer hackers as a proof of concept that arbitrary code can be executed through an exploit where code should not be allowed to be executed, for example, on Sony's Playstation Portable. This is the first step into making home-made content ("homebrew") usable on such a device.