Sorry for the errors in the code.I am new to this.This is the corrected code

use strict;
  my($num2,$num1, $binary,$j );
print "enter the number\n";
$j=<>;
$num2=rand 2**$j;    
$num1=int $num2;
$binary = dec2bin($num1);

print "binary=$binary\n";
sub dec2bin
  {
    my $str =join '', unpack "B32", pack "N", shift;
    $str=substr($str,-$j);    
    return $str;
  }
[download]

regards,
ruben