Is the md5sum linux command working right?

According to Wikipedia, the md5 sum of an empty string is d41d8cd98f00b204e9800998ecf8427e

I confirmed this with my md5 library

However, when I run

echo "" | md5sum

in my linux shell, I get 68b329da9893e34099c7d8ad5cb9c940 -

In fact, none of my hashes match the output of the md5sum command.

Any thoughts on this discrepancy?

With that command, you are calculating the md5sum of a single newline character. Try instead:

echo -n "" | md5sum