Programming Ruby : the pragmatic programmers' guide.

MLA

Thomas, Dave, Chad Fowler, and Andy Hunt. Programming Ruby : the Pragmatic Programmers' Guide. 2nd ed. Raleigh, North Carolina: The pragmatic bookshelf, 2005.

APA

Thomas, D., Fowler, C., & Hunt, A. (2005). Programming Ruby : the pragmatic programmers' guide. 2nd ed. Raleigh, North Carolina: The pragmatic bookshelf.

Chicago

Thomas, Dave, Chad Fowler, and Andy Hunt. Programming Ruby: The Pragmatic Programmers' Guide. 2nd ed. Raleigh, North Carolina: The pragmatic bookshelf, 2005.