Util to load from flatfile?

I am in search of a flexible tool that will let me load new rows and update columns of existing rows from an ASCII flat file. If the ASCII file contains new primary key values, then the utility should insert those new rows. If the ASCII file contains primary key values of existing rows, then the utility should update the fields in those rows with the information from the ASCII file. It hard to believe that Informix doesn't give this functionality, since our ancient version of Unify db did this. Hoping I don't have to code it myself... Thanks for any tips, -Wes