Per man definition, this command gets the input from a file.

```
$ command -r FILENAME

```

Suppose that `FILENAME` is a file containing a list of filenames, as it was generated using `ls > FILENAME`.

How can I, instead, feed the command with the result of `ls` directly? In my head something like this should be possible:

`$ ls | command -r`

But it doesn't, the output of `ls` doesn't get hooked as an argument. Output:

```
Usage: command -r FILENAME
error: -r option requires an argument

```

How could I obtain the desired effect?