B<add\-shell> copia I<etc\/shells> in I<etc\/shells\.tmp>, aggiune le shell specificate in quel file, se non sono già presenti, e ricopia il file temporaneo in I<etc\/shells>. ###>B<add\-shell> copies I<etc\/shells> to I<etc\/shells\.tmp>, adds the given shells to this file if they are not already present, and copies this temporary file back to I<etc\/shells>.