Well, the first thing wrong with your code is that you start with empty arrays, and the only place where anything is pushed into these arrays is inside a loop over the array elements:  for $value (@array) -- and since there are no array elements to start with, the push call is never reached.

Apart from that, there seems to be a disconnect between your stated purpose and the design of your code, and there are some pending questions. How many characters do you plan to draw? Given a 250x250 (pixel) space, the characters will overlap more or less quickly (depending on the font size you're using), even though you don't re-use the same coordinates. If there is a limited number of characters to draw, you could "pre-select" a random set of coordinates by generating an x array and a y array of equal size (number of elements == number of characters to draw), making sure that each array is limited to unique values (something similar to suggestions provided in this thread: Select three random numbers between 1..10

On the other hand, wouldn't it be okay if you use the same x or y coordinate more than once, so long as you don't repeat any given combination of x and y? If so, then you should be keeping a hash whose keys are strings like "123 78" -- that is, just the x and y integer values for a drawn letter, separated by a space. If you pick any two integers at random, it's very unlikely that it would match an existing point, but if it does, you'll find out quickly by testing  if ( exists( $drawn{"$xco $yco"} ))

update: Oh yeah -- and that logic error that Mr. Muskrat alluded to... ooooh, it's quite the unpleasant sort. Look at your "for" loops, imagine that you start out with three values in @xco, and you have a fourth new random x coordinate (which happens not to match the other three). How many pushes do you want to do into @xco? And how many will actually be done by the code you've posted?