What application is using a particular file? I have some FileMaker databases being served for dev purposes and I keep bumping into occurrences where the database/file is locked and I can't make changes to it.  

How can I determine what application is touching/using this file so I can kill it?
Have you tried using the terminal command


  $ lsof 'Filename'


For a more detailed look at the file use

$ lsof | grep -f 'Filename'


Should give you the command that is using it and also the PID of that file