It is not clear that the script will atuomatically die upon the block device filling. The print statement will probably fail, however. So I would try something like this (untested):

#!/usr/bin/perl -w

die "Usage: hexperlscript <blocksize> <destination file>\n" unless @AR
+GV == 2;
my ($input, $output) = @ARGV;
die "Blocksize must be divisible by 512.\nExiting.\n" unless $input % 
+512== 0;
$input /=  2;
open ( DEST, '>>', $output )
   or die "Cannot create ouput file. $! \n";
while (1) {
   for (0..0xff) {
      my $n = sprintf "%02x", $_;
      print DEST $n x $input
         or die "Could not print: $!\n";
   }
}
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