Parameter and Command Reference > Connector Framework Server Parameters > Import Tasks and their Parameters > HashN 

HashN 
Specify a file containing a Lua script to use for family hashing. The script inserts an MD5 field into the document, which is a hash of the document’s unique fields.
In the example below, hash.lua should be (as this uses the file contents):
function handler(document)
return false
end
The hash is calculated from the whole document and it does not matter whether it is text or binary, the hash is calculated from the actual original imported file.
 
Hash0=hash.lua