[Typo3] TypoScript - copy a value

[Matt Valenti]

I guess I don't get TypoScript at all!  I have the following which should be 
trivial but yet again - I'm stumped.  I simply want to make image.file = 
<url parameter>.  I'm embarrassed to admit I've spent 2 hours on this 
already.  Thanks!

temp.imageExpand = IMAGE
temp.imageExpand {
  10 = TEXT
  10.data = GPvar:fn
  file < .10.value
}