Okay, since I plan to upload old backup archives to the cloud for fear to lose data integrity, I wanted to calculate the MD5 hash of these archives before any manipulation. OSX has natively the MD5 command provided by OpenSSL but no argument to check automatically a file checksum against another file which would contain its checksum.
And the -r generates broken MD5SUMS pattern output (the default OpenSSL star is stripped)!

In order to be able to use the md5sum command on OSX like on other Unix platforms, I developed a small script that will behave alike. I hosted it