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- The command name – here ls (list files)
- A command can be any of the built-in Linux/Unix commands, or the name of a user-written script or program
- One or more options, usually noted with a leading dash (-) or double-dash (--).
- -l in example 2 (long listing)
- --help in example 3
- Options are optional – they do not have to be supplied (e.g. example 1 above)
- One or more command-line arguments, which are often (but not always) file names; these are often optional
- e.g. .profile in example 4
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