The quick ways to do what I think you are doing are to use either pack and unpack or printf/sprintf. Something more analogous to your method can be done using unshift to build an array of ones and zeros depending on whether the decimal value leaves a remainder when divided by two then shifting it right one bit, doing this eight times then finally joining the array into a string representing the binary value.

knoppix@Microknoppix:~$ perl -E '
> $dec = 167;
> say unpack q{B*}, pack q{c}, $dec;
> printf qq{%08b\n}, $dec;
> unshift @bits, do {
>    my $bit = $dec % 2 ? 1 : 0;
>    $dec >>= 1;
>    $bit;
>    } for 0 .. 7;
> say join q{}, @bits;'
10100111
10100111
10100111
knoppix@Microknoppix:~$
[download]

I hope this is helpful.