Ellen Siever: Linux in a Nutshell. O'Reilly Media, Inc., 2005, s. 695, seria: Nutshell handbooks. ISBN 978-0-596-00930-4. [dostęp 2016-07-05]. Cytat: whence [...] Korn shell only. Show whether each command is a Unix command, a built-in command, a defined shell function, or an alias..
