Login shells typically ...

Yeah, that is the same generic stuff I've read all over the place, that doesn't explain how login shells determine if they're login shells

Supposedly both zoid and psh can be run as login shells ( chsh ` which psh` ) but there is nothing obvious about how they determine when they're run as login-shells

Here you can see http://search.cpan.org/grep?cpanid=GREGOR&release=psh-1.8.1&string=login&i=1&n=1&C=4

lib/Psh/OS/Win.pm

80-}
81-
82-sub inc_shlvl {
83-     if (! $ENV{SHLVL}) {
84:             $Psh::login_shell = 1;
85-             $ENV{SHLVL} = 1;
86-     } else {
87:             $Psh::login_shell = 0;
88-             $ENV{SHLVL}++;
89-     }
90-}
91-
[download]

but that doesn't look spectacularly useful/portable