md5sum outputs '-' when using stdin

[coreutils]

eg:

$ echo 'hello world' | md5sum
6f5902ac237024bdd0c176cb93063dc4  -

What's use is the '-'?

Obviously it indicates the file content it taken from the standard input, but 
is that of any actual use?

I'm finding that I always end up having to strip it off so I can isolate the 
actual hash. It's a minor irritation, but I did wonder if it actually serves 
any purpose.

$ md5sum --version
md5sum (GNU coreutils) 8.30
Copyright (C) 2018 Free Software Foundation, Inc.
Licence GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Ulrich Drepper, Scott Miller and David Madore.

dwater