Can you 'checksum' a file to see if it was changed?

[Bill Irwin]

I would like to know if there is a command under SCO XENIX 2.3.3
that will produce a checksum on a file, so that later, another
checksum could be compared to the first;  and if different, you
would know that the file had been modified.

Looking at the byte size of the file is a fairly good indicator
if it has been modified, but changes can be made to files that
leave the byte size the same.

Ideally, the command would produce a checksum that could be
stored in a file along with the checked file's name.  Is there
such a beast?
-- 
Bill Irwin    -       The Westrheim Group     -    Vancouver, BC, Canada
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