#!/usr/bin/perl --
use strict;
use Inline C => Config => BUILD_NOISY => 1;
use Inline C => <<'END_C',  NAME => 'modSV', CLEAN_AFTER_BUILD => 0;


#include <stdlib.h> /* setenv/getenv */

char* modSV() {
    return getenv("HORSEY");
}

END_C


use Data::Dump qw/ dd /;
dd( $ENV{HORSEY} => modSV() );
$ENV{HORSEY}='Neigh';
dd( $ENV{HORSEY} => modSV() );
__END__
(undef, undef)
("Neigh", "Neigh")