Linking to another file.

Ok,

lets say there is a client program X.exe that uses the files y.dat and z.dat as a source of information. (extensions are made up). Now lets say I want to switch y.dat with a modified version of y.dat. The y.dat file however, is very large, and copying to create the switch would take forever. Is there anyway I could code a program to create a file y.dat, that would link to either the original or modified depending on what the user wants? In other words, to change the path without having to move the large files. Note, I don't have access to the source of x.exe. Thanks very much.

-waffles

I can't say I 100% understand what you're trying to accomplish...
However, to create a path that can be redirected to different versions of y.dat use subst
(Type help subst in a shell window)

Well basically. X.exe accesses y.dat. It's behavior is based on y.dat. If I modify y.dat, x.exe behaves differently. I have two versions of y.dat. y.dat is very large. How can I easily determine which y.dat x.exe accesses without having to move a large amount of data. In other words, could I create my own y.dat, which x.exe accesses, that would in turn load the y.dat in a different folder that I want.