You're not using strict, and the script is a horrible mess. I suggest a complete rewrite.

At least the empty file will likely come from $write_data not being what you think it is. It is assigned to by this line of code:

$write_data="$${paramname}:::";
[download]

... and I don't even want to track down to what global variable name is stored in $paramname and where it is then dereferenced to.