Create command-line.md

Adding a small command line explanation

terms/command-line.md

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+# Command Line
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+The command line is a text-based way of interacting with your computer. Another way of looking at it is that the command line is a program that accepts commands as text input and converts them into appropriate operating system functions.
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+There are other words that can be used synonymously with "command line." Here are some of them:
+- _bash_ - the programming language used in the command line. (Yes, we tricked you, you're already programming!) Short for "Born Again SHell," for reasons people on the internet will happily tell you about.
+- _the terminal_ - Particularly used to refer to the command line on macOS. This term made more sense when universities used mainframes and every computer was only a terminal.
+- _the shell_ - The part of an operating system that interacts with a human. Technically, anything you do in a graphical interface is also in a shell, but in practice this is just another synonym for the command line.
+- _cli_ - "command-line interface," this is a super technical term for the command line used to impress everyone around you.