The concept of "drive" is uncommon, so there's no standard command. There could be function in one of the Win32 modules, but I haven't found one. I can't even find a Win32 system call that gets the current drive (just one that returns the current directory, with drive).

sub getcwdrv {
   return getcwd() =~ /^([a-zA-Z]:)/ && uc($1);
}
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