Science Fair Project Encyclopedia
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.
Here are some commands given to a Unix or Unix-like operating system:
This cd command changes the user's place in the directory tree from their current position to the directory /home/pete.
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
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).
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