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.
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).
See also