Why does < exist to redirect to stdin?

Question

Question

Why do shells implement alternative means like <<<, < <(command) and < /dev/fd/* to redirect something to stdin when pipes do exist?

Example

The | way (classic pipes)

echo 'text' | sed 's/x/y/'
# or
cat - | sed 's/x/y/' # type text afterwards

The <<< way

sed 's/x/y/' <<< 'text'

The < <(command) way

sed 's/x/y/' < <(echo 'text')
# while <(command) becomes a file descriptor like
sed 's/x/y/' < /dev/fd/42

---

All of them return teyt.

Answer 1

Because a pipe must be fed by a process. The < redirection doesn't need a process, it can be fed by a file. The < redirection was also created long before the <<< and <( ...) operations were invented.

And it's also a complement (counterpart) to the > output redirection. Having basic functions that are complementary to each other is a good thing.

Answer 2

Sotto goes into largely aesthetic reasons, but there are also technical ones. For example, pipes typically result in a subprocess for the right hand side, which means that you cannot set states or variables that you expect to be available later there. Compare:

$ echo foo > 1
$ line=bar; cat 1 | read -r line; echo "$line"
bar
$ line=bar; read -r line < 1; echo "$line"
foo