Command (computing)

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In computing, a command is an instruction received via an external interface that directs the behavior of a computer program. Commonly, commands are sent to a program via a command-line interface, a script, a network protocol, or as an event triggered in a graphical user interface.

Many commands support arguments to specify input and to modify default behavior. Terminology and syntax varies but there are notable common approaches. Typically, an option or a flag is a name (without whitespace) with a prefix such as dash or slash that modifies default behavior. An option might have a required value that follows it. Typically, flag refers to an option that does not have a following value. A parameter is an argument that specifies input to the command and its meaning is based on its position in the command line relative to other parameters; generally ignoring options. A parameter can specify anything, but often it specifies a file by name or path.

The term command is sometimes also used for internal program instructions, but often other terms are more appropriate such as statement, expression, function, or conditional.^[1] For example, printing a message in Bash is via the command printf, while in Python it is via the function print().^[2] Further, some aspects of adjacent technology are conflated with commands. For example, conditional logic in Bash and Python is called an expression^[3][4] and statements in Java.^[5]