CertiGuide to A+ (A+ 4 Real)  9  Chapter 5: The Linux Operating System

/var 1 The Command Line

Linux System has two major user interfaces, the command line and a GUI interface operating through the X Windows system. The X Windows GUI interface will be presented separately. The command line interface is an important interface that every Linux administrator should understand and know how to use. For those folks coming from a Windows background it is analogous to the DOS interface, but greatly predates the DOS interface and is significantly more powerful. It is the original interface for a true multi-user, multitasking operating system - UNIX.

Users interact with the command line through a variety of flavors of interface called shells. The default and most commonly used shell in the Linux world is called the Bash shell, short for the Bourne Again SHell. The Bash shell is essentially a rewrite of the original UNIX Bourne shell, with a super set of commands, add-ons and plug-ins. The result is that shell scripts (scripts are small programs which combine shell commands to provide some added function) written for the Bourne shell will all usually run in the Bash shell however the reverse is not always true.

Most Linux distributions also support several other shells. The csh (in Linux actually the tcsh, an open source equivalent).This has syntax similar to the C programming language, the ksh also known as the Korn shell (an advanced set of the Bourne shell but with a syntax that can be difficult for beginners), and to name another one: the zsh shell. The Bash shell while being a powerful tool, for both novice and advanced users is probably the best shell for beginners to use.

Shell interfaces are sometimes perceived as being difficult, hard to learn and unappealing. However, for the Linux administrator it is essential to become proficient in using the shell interface, especially in the server environment. With systems running server functionality, it is a waste of memory and CPU bandwidth administering or interacting via a GUI interface. Since a server usually only provides information through communication port and not through a video terminal directly attached, the system must deliver this information as quickly as possible. Wasting performance on running a nonessential GUI interface is usually to be avoided. Additionally the administrator will find that many basic administrative functions are easier to handle from the command line than from the GUI interface.

/var 1 The Command Line