I noticed these old threads on MD5 and figured I'd update them in case people find them by searching.
This command was added to Opus a while ago:
GetSizes NODESELECT MD5
If you run it with no files selected then it will calculate MD5 checksums for all files in the dir, or if you run it with some files selected then it'll only do the selected ones. Either way it ignores file size and will calculate the checksums of large files, unlike when you just add the MD5 column where large files will be skipped to avoid taking a long time and accessing the disk a lot.
You can use the registry to change the max size limit that is used when the column is added. See the bottom of page 179 in the PDF manual:
[quote]NOTE The MD5 Checksum column calculates and displays the MD5 checksum (hash value) of all files in the current folder. Because calculating the checksum may take a significant amount of time, it is disabled by default for files exceeding 5000kb in size. If you wish to increase this limit, set the following registry value to the desired limit in kilobytes (or set to 0 to have no limit at all):
HKEY_CURRENT_USER\Software\GPSoftware\Directory Opus\Config\User
(DWORD) MaxHashSize = [/quote]
The max size is probably worth keeping since you can run the GetSizes command above when you want to calculate MD5 for larger files.
There's also Clipboard COPYNAMES=hash and Clipboard COPYNAMES=hash2 for putting the filenames and their hashes into the clipboard. More on those can be found in the clipboard FAQ.