VMS Help GENCAT, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

   msgfile

     The file specification of a message text source file.  The
     default file type for a message text source file is .MSGX.

   catfile

     The file specification of the message catalog file to be
     created.  If the catfile already exists, a new version is
     created that includes the messages in the existing catalog.  The
     default file type for a message catalog file is .CAT.