About the shell in Unix

In Unix, the shell is a program that interprets commands and acts as an intermediary between the user and the inner workings of the operating system. Providing a command-line interface (that is, the shell prompt or command prompt), the shell is analogous to DOS and serves a purpose similar to graphical interfaces like Windows, Mac, and the X Window System.

On most Unix systems, there are several shells available. For the average user, they offer similar functionality, but each has different syntax and capabilities. Most shells fall within one of two classes: those descended from the Bourne shell (that is, sh), which first appeared in Version 7 Unix, and those from the C Shell (that is, csh), which made its debut in BSD. Nearly every Unix system has these two shells installed, but may also have several others: bash, ksh, tcsh, and zsh.

For more, see About Unix shell differences. To determine what options are available for your login shell (that is, your default shell), look at the file /etc/shells on your system.

Most shells double as interpreted programming languages. To automate tasks, you may write scripts containing built-in shell and Unix commands. When you execute a script, the shell interprets these commands as if you had entered them from the command-line prompt. Compared to compiled programs, shell scripts are slow but easy to write and debug.

Note:
In general, shells of the Bourne shell class are better for scripting than those derived from the C shell.

To Unix, the shell is just another program. For this reason, any program can be designated a login shell in /etc/shells. For example, some Emacs users pride themselves on never needing a traditional shell prompt.

At Indiana University, for personal or departmental Linux or Unix systems support, see Get help for Linux or Unix at IU.

This is document agvf in the Knowledge Base.
Last modified on 2019-02-14 11:19:28.

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