Terminology - The word command

Question

I have some confusion about the word "command".

Does the term command refer to:

1. What the user types in a shell? Ex: 'The "man ls" command will display help about the ls command.'
   
2. The program that gets called by the shell? Ex: "The man command allows you to get help about commands".
   
3. The name of the program that gets called by the shell. Ex: "Enter the man command followed by the name of the command"
   
4. All of them?
   

Answer 1

I responded in comments that focused on different aspects as you clarified the question. See if this is clearer.

A command is a human readable "sentence" that is entered in a command line or terminal to accomplish an action. The entire sentence is the command, defining exactly what you want to do. That human readable string is converted to the system commands that accomplish the task.

• A command can be a single word, just a "verb". That word can be a predefined trigger for code built into the command shell, or the name of an executable file. It is only a "command" if you use it in that way.

  For example, chkdsk.exe is a Windows program that you can execute by typing chkdsk.exe (or chkdsk) in a command line. It isn't a command until you create a command using the name.

  Shell commands aren't stand-alone programs, so you can't refer to them as programs, utilities, or apps. They exist only as predefined words in the shell. They're referred to as "commands" because that describes the form of their existence. When you get information about a shell command, as in man ls, you aren't using ls as the "verb" in the command. In that case, "command" doesn't describe its usage, only its nature.

• A command can contain different "parts of speech". In addition to the "verb", there can be words that modify or filter the action, identify things, or act as a placeholder for variable information that gets substituted at execution. ls could be the verb in a command, if the goal is to execute it, or as in your man ls example, it can be just a qualifier. Either way, if it's part of the command string, it's part of the command.

• A command can be a compound sentence containing multiple actions strung together (more than one "verb").

• Command parameters that modify the action may not be the "verb" in your command, but behind the scenes may actually be additional "verbs" in the translated command the system gets.

Answer 2

The word "command" is synonymous to many features in computing that, understandably, it is easy to get confused.

• There is the generic "command", which means to issue an instruction.

  In you case the command man lsis made out of two seperate commands.

  Manis shorthand for the command manual, a help guide for other commands in linux. Ls is shorthand for the command list. In it's default use, it lists the files located in the current working directory.

  When the command is issued together, man ls, it fetches the help page for the list command. Many commands are concatnated this way to allow for more functions and options.

• There is also others who use "command" to refer to the the CLI, command line interface of Linux or CMD, command prompt of Windows.

  These are basically interfaces to issue the commands mentioned above. The details between the difference between these interfaces are highlighted here.

So a sentence like...

"Entering the command man into the command line interface will show the help page of commands such as ls and cat".

... is perfectly valid.