in reply to
how to tell if a file is still being modified
Thanks for all the replies. The best of all possible worlds would be if we could control the FTP sender in addition to the receiver and just set up some handshake protocol there, but that'd make life too easy x). The poll-the-file-until-it-no-longer-changes is something that would most certainly work but it just feels a li'l brittle.
I've already implemented it using fuser but the thought that the production machine's OS might not always have fuser available crossed my mind and wouldn't let go (the warning in Linux::Fuser stating that "even then it may not work on other than 2.2.* kernels" made me squirm a bit too).
In any case, fuser seems to be working fine (though this thing is a bit awkward to test) . Once again, I've shamed my ancestors and forgotten to heed the potential wisdom of YouArentGonnaNeedIt .
Thanks again for all the input!