?UserData, ?Value)Value is the value for Field in UserData.
Defined fields are:
:- use_module(library(uid)).(can be autoloaded)
- Name of the user
- Password hash of the user (or
x if this is not accessible)
- Numeric user id of the user
- Numeric primary group id of the user
- The gecos field
- Home directory of the user
- Default (login) shell of the user.