A "hello world" program is a computer program that 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 many embedded systems, the text may be sent to a one or two-line liquid crystal display (LCD), or some other appropriate signal, such as an LED being turned on, may substitute for the message.
A "hello world" program 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.
Here is an "Hello World" program collection that includes 338 Hello World programs in many more-or-less well known programming languages:
I didn't know there exists that much programming languages :) I think this includes not only the programming languages, but whatever that can write any output to anywhere :)
And here is a funny joke from GNU: How the way people code "Hello World" varies depending on their age and job:
The chief executive version is really funny, isn't it? :)