What BASIC intepreters are available?
Searching apt reveals
basic256- educational BASIC programming environment for childrenyabasic- Yet Another BASIC interpreter
basic256 seems it might be a little better suited for the user, but I'm not sure how closely that dialect will match whatever is in his programming book, which might be frustrating.
Homepage here - http://www.basic256.org/index_en
yabasic seems closer to standard BASIC, but I really have no first-hand experience with either.
Good luck.
Gambas is the nearest equivalent to Visual Basic (It is quite geared towards desktop apps), so would be good if your friend was using Visual Basic.
Gambas is a free development environment based on a Basic interpreter with object extensions, a bit like Visual Basic™ (but it is NOT a clone !). Read the introduction for more information.
With Gambas, you can quickly design your program GUI with Qt or GTK+, access MySQL, PostgreSQL, Firebird, ODBC and SQLite databases, pilot KDE applications with DCOP, translate your program into any language, create network applications easily, make 3D OpenGL applications, make CGI web applications, and so on...
If he is more interested in making games, sdlBasic would be a better option:
sdlBasic
is a small, efficient and multiplatform basic interpreter aimed to game creation using the power of SDL library, it was inspired by the old and glorious AMOS.