#!/usr/bin/perl

use v5.12;
use strict;
use warnings;

package SpyHash {

        use Tie::Hash; # for Tie::StdHash
        use Carp qw( carp );

        our @ISA=qw( Tie::StdHash );

        sub STORE
        {
                my ($self,$key,$value)=@_;
                $key=~/^CH?LD$/ and carp "Assign to key $key";
                return $self->SUPER::STORE($key,$value);
        }

        sub DELETE
        {
                my ($self,$key)=@_;
                $key=~/^CH?LD$/ and carp "Delete key $key";
                return $self->SUPER::DELETE($key);
        }

}

tie %SIG,'SpyHash';

$SIG{'CHLD'}=sub { 'just a dummy' }; # this line should be reported
require Net::DNS; # Any module messing with $SIG{'CHLD'} should be reported from here
Net::DNS->import(); # ... or here