Option to return a Adler32 or MD5 checksum cleanly, for processing in workflow

[onnozweers]

There is an old issue in the GridScripts repo:

sara-nl/GridScripts#3

This is a (slightly mislocated) request for an ada option to return the checksum cleanly, without any other output.

Currently, the format is:

filename  ADLER32:xxxxx  MD5SUM:xxxxxxxxxxx

Users sometimes want to get only the desired checksum and nothing else, to integrate in their workflow.

Currently the options are:

	  --checksum <file>
	      Show MD5/Adler32 checksums for file.
	  --checksum <directory> [--recursive]
	      Show MD5/Adler32 checksums for files in directory.
	  --checksum --from-file <file-list>
	      Show MD5/Adler32 checksums for files in the list.

We could change the first option to:

	  --checksum <file> [--adler32|--md5]
	      Show MD5/Adler32 checksums for file.
	      If --adler32 or --md5 is specified, only print that
	      specific checksum, and nothing else.