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Kernighan is good at explaining things, so I'm guessing he wanted to make it as simple as posible, some of those just don't roll of your tongue as well as the aliased versions

> existing UNIX programs (on your machine).

They emphasize that users build their own vocabulary. And it is quite possible these command were shared inside AT&T.

Maybe the idea is that every shell script compromised of existing, simpler commands, is automatically itself a "command" in UNIX. Obvious and simple today, but not a common concept when this video was made.

Wasn't that the same in operating systems like MS-DOS and its predecessors, and on Apple computers as well?

Well yeah I guess if you are thinking in terms of batch scripts, but DOS didn't exist until 1980, and UNIX had already been doing this within a multiuser, multitasking environment since at least 1972.

Oh, my bad, I confused the decade.

They may be, or not. Long ago grep was composed of an ed script (g/re/p), and a spell checker was trivially done this way over grepping /usr/share/dict/words.

The point is to show pipes to the public so they understand command chaining.