Here is a video version, if you prefer it:
This may be a very simple question – what is a command? What is a command in the context of the Linux shell environment?
Commands are, in essence, running a program with options and arguments. (Barrett, 2016) If you write, for example, ls -l file.txt, you are calling a program called ls with the option -l and the argument file.txt. But wait a minute – how does the operating system know where to find the ls program? This is not the focus of this article so we don’t currently care. As far as we are right now concerned, the operating system “does its magic” so it can find the program ls and call it with the specified options.
There are a lot of things you can do with commands – commands can be piped, meaning output of one command is input to another and there can exist scripts which within themselves contain lots of commands. But again, essentially, a command is just a single program, with its options and arguments.
Hope you found this useful!
Barrett, D. J. (2016). Linux pocket guide (3rd ed.). O’Reilly Media. Pages 3-4
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