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In [[computing]], a '''command''' is an instruction received via an external [[Interface (computing)|interface]] that directs the behavior of a [[computer program]]. Commonly, commands are sent to a program via a [[command-line interface]], a [[scripting language|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 character|whitespace]]) with a prefix such as [[dash]] or [[Slash (punctuation)|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 (computing)|file]] by [[filename|name]] or [[file path|path]].
Specifically, the term ''command'' is used in [[imperative programming]] languages. The name arises because [[statement (programming)|statements]] in these languages are usually written in a manner similar to the [[imperative mood]] used in many [[natural language]]s. A statement in an imperative programming language would then be a sentence in a natural language, and the command would be the [[Predicate_(grammar)|predicate]].
The meaning ofterm ''command'' is highlysometimes dependentalso onused context.for Forinternal program exampleinstructions, somebut authorsoften referother toterms are more appropriate such as [[ Conditional_statement ( computer_programmingprogramming)| conditionalsstatement]] , as[[Expression commands(computer science)|expression]], [[Function (computer programming)|function]], or [[Conditional (computer programming)|conditional]].<ref>Maurizio Gabbrielli, Simone Martini (2010). Programming Languages - Principles and Paradigms. Springer London, ''6.3.2 Conditional Commands'', p. 140</ref> For example, printing a message in Bash is via the ''command'' [[Printf (Unix)|printf]], while theyin arePython calledit is via the '' expressionsfunction'' print().<ref>{{cite web | url = https://docs.python.org/3/library/functions.html#print | access-date = 23 October 2023 | title = Built-in Functions - print | publisher = python.org }}</ref> Further, some aspects of adjacent technology are conflated with commands. For example, conditional logic in Bash and Python is called an ''expression''<ref>{{cite web | url = https://docs.python.org/3/reference/expressions.html | access-date = 23 October 2023 | title = Conditional expressions | publisher = python.org }}</ref> or Bash<ref>{{cite web | url = https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html | access-date = 23 October 2023 | title = Bash Conditional expressions | publisher = gnu.org }}</ref> and ''statements'' in Java.<ref>{{cite web | url = https://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html | access-date = 23 October 2023 | title = The if-then and if-then-else Statements | publisher = oracle.com }}</ref> ▼Many programs allow specifically formatted [[Parameter (computer science)|arguments]], known as [[Command-line flag|flag]]s or options, which modify the default behaviour of the program, while further arguments may provide [[object (computing)|object]]s, such as [[file (computing)|file]]s, to act on. As an analogy to a [[natural language]], the flags are [[adverb]]s, while the other arguments are [[object (grammar)|grammatical object]]s.
==Distinction between ''command'' and [[Expression_(computer_science)|expression]], [[Statement_(computer_science)|statement]] and [[Function_(computer_programming)|function]]==
▲The meaning of ''command'' is highly dependent on context. For example, some authors refer to [[Conditional_(computer_programming)|conditionals]] as commands <ref>Maurizio Gabbrielli, Simone Martini (2010). Programming Languages - Principles and Paradigms. Springer London, ''6.3.2 Conditional Commands'', p. 140</ref> while they are called ''expressions'' in Python<ref>{{cite web | url = https://docs.python.org/3/reference/expressions.html | access-date = 23 October 2023 | title = Conditional expressions | publisher = python.org }}</ref> or Bash<ref>{{cite web | url = https://www.gnu.org/software/bash/manual/html_node/Bash-Conditional-Expressions.html | access-date = 23 October 2023 | title = Bash Conditional expressions | publisher = gnu.org }}</ref> and ''statements'' in Java.<ref>{{cite web | url = https://docs.oracle.com/javase/tutorial/java/nutsandbolts/if.html | access-date = 23 October 2023 | title = The if-then and if-then-else Statements | publisher = oracle.com }}</ref>
Similarly, writing to [[Standard_streams#Standard_output_(stdout)|stdout]] is done in Bash with the builtin ''command'' [[Printf_(Unix)|printf]], while it is done with the built-in ''function'' print() in Python.<ref>{{cite web | url = https://docs.python.org/3/library/functions.html#print | access-date = 23 October 2023 | title = Built-in Functions - print | publisher = python.org }}</ref>
==Examples==
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