Of course, graphical windowing systems also fill this need. Technically, Windows 95 provides a graphical shell, and the X Window system is another kind of graphical shell. But “shell” is commonly used to mean “command-line shell.”

Needless to say, the hackers who work on shells aren’t satisfied with simply launching commands. Your shell has a bewildering number of convenient and powerful features if you would like to take advantage of them.

There are countless different shells available; most are based on either the Bourne shell or the C shell, two of the oldest shells. The original Bourne shell’s program name is sh, while csh is the C shell. Bourne shell variants include the Bourne Again Shell from the GNU project (bash, the Debian default), the Korn shell (ksh), and the Z shell (zsh). There is also ash, a traditional implementation of the Bourne shell. The most common C shell variant is tcsh (the t pays tribute to the TENEX and TOPS-20 operating systems, which inspired some of tcsh’s improvements over csh).

bash is probably the best choice for new users. It is the default and has all the features you’re likely to need. But all the shells have loyal followings; if you want to experiment, install some different shell packages and change your shell with the chsh command. Just type chsh, supply a password when asked, and choose a shell. When you next log in, you’ll be using the new shell.

5.5 Managing Processes with bash

Debian is a multitasking system, so you need a way to do more than one thing at once. Graphical environments like X provide a natural way to do this; they allow multiple windows on the screen at any one time. Naturally, bash (or any other shell) provides similar facilities.

Earlier you used top to look at the different processes on the system. Your shell provides some convenient ways to keep track of only those processes you’ve started from the command line. Each command line starts a job (also called a process group) to be carried out by the shell. A job can consist of a single process or a set of processes in a pipeline (more on pipelines later).

Entering a command line will start a job. Try typing man cp, and the cp manual page will appear on the screen. The shell will go into the background and return when you finish reading the manual page (or you can press q to quit rather than scrolling through the whole thing).

But say you’re reading the manual page, and you want to do something else for a minute. No problem. Press Ctrl-z while you’re reading to suspend the current foreground job and put the shell in the foreground. When you suspend a job, bash will first give you some information on it, followed by a shell prompt. You will see something like this on the screen:

NAME cp - copy files SYNOPSIS cp [options] source
--More--
[1]+ Stopped man cp
$