Here's the code as I've deciphered it:
open (writefile,">>",$target_full_path) || die "Can't open $target_ful
print $fetchdata; #it is working
print writefile $fetchdata; # not appending
$rowcount++; #here it is counting
When you open, it doesn't die? Maybe try printing $target_full_path to make sure it has what you think it does. Your argument to die should include $! in it somewhere since that will have the error that caused open to fail.
I'm sorry, I don't see why this wouldn't work. What was the slight modification that causes it to break?