Why you are getting a blank page depends on what the full CGI is doing... However you really need to think about what you expect you code to do.

Your line 5 is effectively creating an one by one array with the value of $incomingdata. Thats what the parenthesis is doing (note you are overwriting the array you set in line 4 if you uncomment), your then using this array in a loop which populates your hash reference. If you only required it to work with the scalar you could get completely rid of the loop.