module to modify user and group accounts

 The Linux::usermod module adds, removes and modifies user and group accounts
 according to the passwd and shadow files syntax (like struct passwd from
 pwd.h). It is not necessary those accounts to be system as long as
 $Linux::usermod::file_passwd, $Linux::usermod::file_shadow,
 $Linux::usermod::file_group, $Linux::usermod::file_gshadow are not in the
 "/etc" directory.