Different implementations of SHA1, which one is correct?
The echo command will include a newline at the end. So when you use echo 'Rosetta Code' | sha1sum you are actually hashing the string Rosetta Code\n.

Do the test using echo -n, the -n flag prevents the trailing newline character. Doing echo -n 'Rosetta Code' | sha1sum gives the same 48c98f7e5a6e736d790ab740dfc3f51a61abe2b5 hash that you were seeing elsewhere.