Hello, World!

A "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. It is often the very first program people write when they are new to a language.

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.

While small test programs have existed since the development of programmable computers, the tradition of using the phrase "Hello, world!" as a test message was influenced by an example program in the seminal book The C Programming Language. The example program from that book prints "hello, world" (without capital letters or exclamation mark), and was inherited from a 1974 Bell Laboratories internal memorandum by Brian Kernighan, Programming in C: A Tutorial,:

The C version was preceded by Kernighan's own 1972 A Tutorial Introduction to the Language B, where the first known version of the program is found in an example used to illustrate external variables:

The program prints hello, world! on the terminal, including a newline character. The phrase is divided into multiple variables because in B, a character constant is limited to four ASCII characters. The previous example in the tutorial printed hi! on the terminal, and the phrase hello, world! was introduced as a slightly longer greeting that required several character constants for its expression.

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