Hmm, the example page doesn't convince me, for example
> The diff utility can compare files and print their differences. If we pass it the result of ls commands, we can compare the contents of directories.
No, if you pass the output of ls commands, you might get an error because you'll pass a bunch of files to diff.
And last but not least there's
diff -r directory-a directory-b
I think it was about demonstrating process substitution. You don't pass a bunch of files to diff, you pass the output of ls, as a file, to diff.
I actually thought it was awesome to see that. I use this a lot to diff the output of commands and many people don't know about it.
I wanted to demonstrate the use of the substitution, not the best way to diff directories. Often I tried to create examples that demonstrate multiple concepts or tools at once to save space. But I see your point.