This article is reprinted from the book A Practical Guide to Linux Commands, Editors, and Shell Programming 3rd edition, with permission of the author and publisher ...

While Linux systems install with thousands of commands, bash also supplies a large number of “built-ins”—commands that are not sitting in the file system as separate files, but are part of bash itself ...

Linux is a tried-and-true, open-source operating system released in 1991 for computers, but its use has expanded to underpin systems for cars, phones, web servers and, more recently, networking gear.