Hello world!

“Hello, World!” program is a computer program that outputs or displays “Hello, World!” to a user. Being a very simple program in most programming languages, it is often used to illustrate the basic syntax of a programming language for a working program.[1] It is often the very first program people write when they are new to a language.

Purpose

A “Hello, World!” program is traditionally used to introduce novice programmers to a programming language.

“Hello, world!” is also traditionally used in a sanity test to make sure that a computer language is correctly installed, and that the operator understands how to use it.

“Hello, world!” is also used by computer hackers as a proof of concept that arbitrary code can be executed through an exploit where the system designers did not intend code to be executed.

Variations

There are many variations on the punctuation and casing of the phrase. Variations include the presence or absence of the comma and exclamation mark, and the capitalization of the ‘H’, both the ‘H’ and the ‘W’, or neither. Some languages are forced to implement different forms, such as “HELLO WORLD”, on systems that support only capital letters, while many “hello, world” programs in esoteric languages print out a slightly modified string. For example, the first non-trivial Malbolge program printed “HEllO WORld”, this having been determined to be good enough.[10]

There are variations in spirit, as well. Functional programming languages, like LispML and Haskell, tend to substitute a factorial program for Hello, World, as functional programming emphasizes recursive techniques, whereas the original examples emphasize I/O, which violates the spirit of pure functional programming by producing side effects. Languages otherwise capable of Hello, World (Assembly, C, VHDL) may also be used in embedded systems, where text output is either difficult (requiring additional components or communication with another computer) or nonexistent. For devices such as microcontrollersfield-programmable gate arrays, and CPLD‘s, “Hello, World” may thus be substituted with a blinking LED, which demonstrates timing and interaction between components.[11][12][13][14][15]

The Debian and Ubuntu Linux distributions provide the “hello, world” program through the apt packaging system; this allows users to simply type “apt-get install hello” for the program to be installed, along with any software dependencies. While of itself useless, it serves as a sanity check and a simple example to newcomers of how to install a package. It is significantly more useful for developers, however, as it provides an example of how to create a .deb package, either traditionally or using debhelper, and the version of hello used, GNU Hello, serves as an example of how to write a GNU program.[16]