[Fors1k]

Foreigner, У меня не сработало:

user anything-anything-12345678 https://anything.site.com/

Код:

$urls = 'https://site.com/user/anything/anything',
        'https://anything.site.com/anything-anything-12345678/anything',
        'https://anything.site.com/'
cls
$user = ($urls|sls "(?<=(?<!\..+)\.[^\.]+?/)[^/]+(?!.*-\d/)").Matches.Value
$sub  = ($urls|sls "[^/]+?(?=\.(?=.+\.)[^/]+/$)").Matches.Value
$post = ($urls|sls "(?<=-)\d+").Matches.Value

"https://$sub.site.com/$user/$post"

Адова регулярка (с) DJ Mogarych, но на ночь глядя ничего красивее не стал искать)