It's because $binaddr only lives within the eval block. Ditch the eval block and you should be ok.

Update:
I fiddled with it a little just because I've never really messed with binary operations.

#!/usr/local/bin/perl -w 
  
use strict;
  
use Net::IP qw/:PROC/;
  
#
# create your Net::IP object
#
my $ip_addr = Net::IP->new( "192.168.0.20" );
  
#
# $ip_int becomes a Math::BigInt object
#
my $ip_int = ip_bintoint( $ip_addr->binip );

print "IP Address: ", $ip_addr->ip,
      "\nBin: ", $ip_addr->binip,
      "\nInt: ", $ip_int->numify(),
      "\n";

#
# turn the Integer into a vanilla scalar
#
my $int_ip = $ip_int->numify();
  
#
# Now start from the integer and go backwards
#

my $bin_from_int = sprintf( "%b", $int_ip);
my $ip_from_bin = ip_bintoip( $bin_from_int, 4);

print "\n\nInt: $int_ip\n",
      "Bin: $bin_from_int\n",
      "IP:  ", $ip_from_bin, "\n";
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