Introducing the Linux shell
Linux has its roots in the Unix operating system, and one of its main strengths is the command-line interface. In the old days, this was called the shell. In Unix, the shell is invoked with the
sh command. The shell is a program that has two streams: an input stream and an output stream. The input is a command given by the user, and the output is the result of that command, or an interpretation of it. In other words, the shell is the primary interface between the user and the machine.
The main shell in major Linux distributions is called Bash, which is an acronym for Bourne Again Shell, named after Steve Bourne, the original creator of the shell in Unix. Ubuntu, Fedora, CentOS, RHEL, Debian, and openSUSE all use Bash as their default shell. Alongside Bash, there are other shells available in Linux, such as ksh, tcsh, and zsh. In this chapter, we will cover the Bash shell, as it is the most widely used shell in modern Linux distributions.