#!/usr/bin/perl -w
use strict;

#get the input
print("\n\nEnter a binary number:");
chomp(my $binary=<STDIN>);

#make sure the number is only 1s and 0s
die "Not a binary number: $!" if $binary =~ /[^01]/

#get the value and print it to the screen
my $decimal = convb2d($binary);
print "Decimal: $decimal\n";

#do the conversion
sub convb2d
{
 my $binary = shift;
 return unpack 
  ( "N", pack("B32", substr("0" x 32 . $binary, -32 )));
}