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In computing, a command is a directive to a computer program acting as an interpreter of some kind, in order to perform a specific task. Most commonly a command is a directive to some kind of command line interface, such as a shell.

Specifically, the term command is used in imperative computer languages. These langauges are called so, because statements in these languages are usually written in a manner similar to the imperative mood used in many natural languages. If one views a statement in an imperative language as being like a sentence in a natural language, then a command is generally like a verb in such a language.

Many programs allow specially formatted arguments, known as flags, which modify the default behaviour of the command, while further arguments describe what the command acts on. Comparing to a natural language: the flags are adverbs, whilst the other arguments are objects.

1 Examples

Here are some commands given to a Unix or Unix-like operating system:

cd /home/pete

This cd command changes the user's place in the directory tree from their current position to the directory /home/pete.

echo "hello"

This echo command prints the text hello out to the standard output stream, which, in this case, will just print the text out on the screen

ls -ltr /bin

This ls command lists files in the directory /bin, also listing all the files in long format (the flag -l), sorted by time (the flag -t), and in reverse order (the flag -r).

2 See also

List of Unix programs
List of DOS commandsA list of DOS commands for Microsoft's DOS operating system follows. Beginning with version 6. 0, the user could get help by typing HELP in the shell prompt. Square brackets indicate optional parameters, while italicized items should be replaced with spec
Formal grammarIn computer science a formal grammar is an abstract structure that describes a formal language precisely, i. a set of rules that mathematically delineates a (usually infinite) set of finite-length strings over a (usually finite) alphabet. Formal grammars

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