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

sub dec2bin {
    my $bits      = shift;
    my $size      = shift;
    my $template  = shift;
    my $str = unpack("B$size", pack($template, $bits));
    return $str;
}

sub bin2dec {
    my $bits     = shift;
    my $size     = shift;
    my $template = shift;
    my $substr = substr("0" x $size . $bits , -$size);
    print "Substring: ".$substr."\n";
    my $pack = pack("B$size", $substr);
    print "Pack: ".$pack."\n";
    my $unpack = unpack($template, $pack);
    return $unpack;
}

my $int2bin = dec2bin( 3 , 8 , "i" );

print "Int2bin: ".$int2bin."\n";

my $binary2int = bin2dec( $int2bin , 8 , "i" );

print "Decimal from binary: ".$binary2int."\n";

__END__

Int2bin: 00000011
Substring: 00000011
Pack: 
Use of uninitialized value $binary2int in concatenation (.) or string at test.pl line 32.
Decimal from binary: