Is backwards redirection the same as a pipe?

Question

In Linux if you type

sort < txtfile

is that the same thing as

cat txtfile | sort

Answer 1

To your title question: No. Getting stdin from file contents (input redirection) is not the same as piping one program's output to another program's input.

But, as your cat actually just prints a file's contents, the result is effectively the same in that example.

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But even just the following produce very different results:

$ cat * | sort
$ sort < *

If there's more than one matching file, the latter will produce

-bash: *: ambiguous redirect

since it's just not as flexible as the former, which will cat all matching files, and pipe them as input into sort.