use Env;
$ENV{'MYVAR'} = '123';
$ENV{'myvar'} = '123';
Env::import;
print "\$MYVAR: $MYVAR\n"
    , "\$myvar: $myvar\n";

##</code><code>##

$MYVAR: 123
$myvar: 123

##</code><code>##

$MYVAR: 123
$myvar: