Christopher Negus - Linux Bible

To exit the shell when you are finished, type exitor press Ctrl+D. If you go to the shell from a Terminal window and you are using the original shell from that window, exiting causes the Terminal window to close. If you are at a virtual console, the shell exits and returns you to a login prompt.

If you have multiple shells open from the same shell session, exiting a shell simply returns you to the shell that launched the current shell. For example, the sucommand opens a shell as a new user. Exiting from that shell simply returns you to the original shell.

You can tune your shell to help you work more efficiently. You can set aliases to create shortcuts to your favorite command lines and environment variables to store bits of information. By adding those settings to shell configuration files, you can have the settings available every time you open a shell.

Several configuration files support how your shell behaves. Some of the files are executed for every user and every shell, whereas others are specific to the user who creates the configuration file. Table 3.6shows the files that are of interest to anyone using the bash shell in Linux. (Notice the use of ~in the filenames to indicate that the file is located in each user's home directory.)

To change the /etc/profileor /etc/bashrcfiles, you must be the root user. It is better to create an /etc/profile.d/custom.shfile to add system-wide settings instead of editing those files directly, however. Users can change the information in the $HOME/.bash_profile, $HOME/.bashrc, and $HOME/.bash_logoutfiles in their own home directories.

TABLE 3.6 Bash Configuration Files

Until you learn to use the vieditor, described in Chapter 5, “Working with Text Files,” you can use a simple editor called nanoto edit plain-text files. For example, enter the following to edit and add stuff to your $HOME/.bashrcfile:

$ nano $HOME/.bashrc

With the file open in nano, move the cursor down to the bottom of the file (using the down arrow key). Type the line you want (for example, you could type alias d='date +%D'). To save the file, press Ctrl+O (the letter O ); to quit, press Ctrl+X. The next time you log in or open a new shell, you can use the new alias (in this case, just type d). To have the new information you just added to the file available from the current shell, type the following:

$ source $HOME/.bashrc $ d 06/29/19

The following sections provide ideas about items to add to your shell configuration files. In most cases, you add these values to the .bashrcfile in your home directory. However, if you administer a system, you may want to set some of these values as defaults for all your Linux system's users.

Your prompt consists of a set of characters that appear each time the shell is ready to accept a command. The PS1environment variable sets what the prompt contains and is what you will interact with most of the time. If your shell requires additional input, it uses the values of PS2, PS3, and PS4.

When your Linux system is installed, often a prompt is set to contain more than just a dollar sign or pound sign. For example, in Fedora or Red Hat Enterprise Linux, your prompt is set to include the following information: your username, your hostname, and the base name of your current working directory. That information is surrounded by brackets and followed by a dollar sign (for regular users) or a pound sign (for the root user). The following is an example of that prompt:

[chris@myhost bin]$

If you change directories, the binname would change to the name of the new directory. Likewise, if you were to log in as a different user or to a different host, that information would change.

You can use several special characters (indicated by adding a backslash to a variety of letters) to include different information in your prompt. Special characters can be used to output your Terminal number, the date, and the time as well as other pieces of information. Table 3.7provides some examples (you can find more on the bash man page).

TABLE 3.7 Characters to Add Information to Bash Prompt