How can I tell which parts of a command are the command name and its arguments?

For this simple example, label the parts like this:

• ls — command name: the program being asked to run.
• -l — option: a word the program uses to adjust what it does.
• notes.txt — argument: the file name the command is being given.

So you could read the line aloud as: “Run ls, use the -l option, and act on notes.txt.” GNU ls documents -l as an option and accepts a file or directory argument. [S2]

One useful distinction: in shell terminology, the words after the command name are arguments, including option words such as -l. Calling -l an “option” describes its role as interpreted by this program. [S1] [S2]

Use the first remaining word as your starting point: Bash describes it as the command name, with subsequent words as arguments. But do not assume every program interprets those arguments in the same way. [S1] An option is an argument the particular program recognizes as a setting or mode; a file name or other value may be another argument. The spelling alone is not a guarantee that something is an option.

A practical method is to identify the command first, then check that program’s own help or documentation for the meaning of each remaining word. For ls, the manual establishes the meaning of -l; another command may use different option conventions. [S2] This guide’s example does not establish conventions for every shell or program.

Here is the labeled exercise:

ls -l notes.txt

1. ls: command name.
2. -l: option supplied to ls.
3. notes.txt: file argument supplied to ls.

GNU Coreutils documents ls as listing file information. It also says that a directory argument makes ls list that directory’s contents, while without a directory argument it acts on the current directory. [S2] In this example the named target is a file, not a directory; the documentation excerpt supports identifying the pieces but does not tell us whether notes.txt exists on your machine or what its displayed information will be.

If you remove the target and type ls -l, the command name and option are still ls and -l. GNU ls then acts on the current directory when no directory argument is given. [S2] That is a behavior specific to this program, not a rule that every command defaults to the current directory.

First, do not split blindly at every space: shell processing can affect the words before a command runs. Bash’s description of the first remaining word applies after shell processing, not necessarily to the untouched characters you initially see. [S1] For a basic line with no quoting or shell expansions, separate the visible words, mark the first as the command name, and then ask what role each later word plays according to that program’s documentation.

Here is a reusable annotation template:

[command name] [option(s)] [value or target argument(s)]

For the example:

ls = command name; -l = option; notes.txt = file argument.

For an unfamiliar line, copy it without running it, mark likely pieces with that template, and verify each uncertain option or argument in the relevant program’s documentation. Do not infer that a word is harmless just from its position; parsing the parts explains structure, not the full effects of an unfamiliar command.