johngg (++) has given you 3 ways to achieve your results, but these require a little more in-depth perl knowledge.

Based on your code, this working version should be simpler to understand:

use warnings;
use strict;

print"Please enter an integer less than or equal to 256: ";
my $decimal =  <STDIN>;
print "Decimal=$decimal\n";
my  @binary = (0) x 8; # Initialize to 8 zeros 
if ($decimal >"256")
      {
          die"\nYou entered an invalid number!\n\n";
      }
for (0..7){
  $binary[7 -$_] = 1 if $decimal & 2**$_;  # Mask out the bit, and set
+ $binary[n]
}
print"@binary\n";
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