Good for using strictures (strict and warnings), but not so good for resorting to a large number of variables to store the bits. An array is a much better way to store a bunch of related data:

#!/usr/bin/perl
use warnings;
use strict;

print "Enter a number between 0 to 256 : ";
my $dec = <STDIN>;
my @bits;

$bits[7] = ($dec & 128) <=> 0;
$bits[6] = ($dec & 64) <=> 0;
$bits[5] = ($dec & 32) <=> 0;
$bits[4] = ($dec & 16) <=> 0;
$bits[3] = ($dec & 8) <=> 0;
$bits[2] = ($dec & 4) <=> 0;
$bits[1] = ($dec & 2) <=> 0;
$bits[0] = ($dec & 1) <=> 0;
printf "The entered decimal number in binary is : %s\n", join '', reve
+rse @bits;
[download]

That makes it easier to manipulate the bits as a group which is quite an advantage when we come to printing it. However there are still too many lines of repeated code. We can fix that by calculating the bit mask from the bit index:

...
my @bits;

$bits[$_] = ($dec & 2 ** $_) <=> 0 for 0 .. 7;
printf "The entered decimal number in binary is : %s\n", join '', reve
+rse @bits;
[download]

But none of that addresses your question about (I presume) handling numbers greater than 256. However, now we have an array we can use whatever number of bits we need so:

...
my @bits;

while ($dec || ! @bits) {
    push @bits, $dec & 1;
    $dec >>= 1;
}

printf "The entered decimal number in binary is : %s\n", join '', reve
+rse @bits;
[download]