Before we get started, we should say that the very easiest way to customize Emacs is by selecting an option from the Options menu and choosing Save Options. This menu is designed to provide easy access to changing frequently used options. For example, you may not like the Toolbar and its icons, feeling that such graphical codswallop is beneath an Emacs user. You can hide the toolbar through the Show/Hide option on the Options menu. Choosing Save Options modifies .emacs so the toolbar is hidden every time you start Emacs. And if you miss the toolbar someday, you can get it back the very same way.
After describing customization methods, this chapter goes on to discuss several generic issues relating to customization, including how to change fonts and colors, modify your key bindings, set Emacs variables, find Lisp packages to load, start modes automatically based on file suffixes, and inhibit any global customization files that may be interfering with your own .emacs settings.
10.1 Using Custom
Emacs now ships with a quirky graphical-but-not interface that allows you to customize most aspects of Emacs without knowing the gory details. This feature, known as Custom, can be accessed by typing M-x custom or by clicking the tools icon on the toolbar.
Type: M-x custom Enter
Emacs displays the startup buffer for Custom (Mac OS X).
10.1.1 Navigating Custom
You can move around in a given Custom screen much the way you do in any other part of Emacs. All of the basic cursor movement commands like C-n and C-p work just as they should. But that's only part of the story in Custom. To accomplish anything useful, you need to activate special words and phrases. Those bits of text in grey boxes that look like buttons are the words and phrases in question.
To activate one of these buttons, click on the button with the mouse or position your cursor inside its borders and press Enter. Figure 10-1 highlights these options.
Figure 10-1. Custom button activation using the mouse cursor (top) and the keyboard cursor (bottom) (Mac OS X)
When you finish looking at a screen, if you are not interested in changing anything, you can type C-x k to kill the current buffer and go back to the previous screen. You can also activate the Finish button in the common header set discussed next.
10.1.2 Common Options
At the top of each page in Custom is a common set of buttons shown in Figure 10-2. These options affect the entire buffer.
Figure 10-2. The actions common to all pages in Custom (Mac OS X)
From here you can perform any of the following tasks:
Set for Current Session
Make immediate changes that last for the duration of this session but will be reset the next time you start Emacs.
Save for Future Sessions
Make immediate changes that last for the duration of this session and will also be in place the next time you start Emacs. These changes are stored in your .emacs file.
Reset
Switch back to the previous values (previous to your current changes, anyway).
Reset to Saved
Switch back to the previously saved values. In this case, "saved" means saved for future sessions. If you haven't made (and subsequently saved) any customizations to a variable, this option has no effect.
Erase Customization
This option pretty much does what it says. Any customizations made by Custom, whether for this or future sessions, are removed. Your own personal entries in your .emacs file should remain intact, but it's always a good idea to make a backup before deleting any information.
Finish
Close this buffer and return to the previous customization buffer or back to the buffer from which you launched Custom. Note that you can also press the q key to activate Finish from anywhere in a Custom buffer.
These options are useful when you modify more than one option on a page and want to save them all at once (and in the same way).
Custom corrals options into customization groups, which are set up in a hierarchy of parent and child groups. To go to the parent group for the group you're looking at, choose the button for the parent group in question following the Go to parent group: prompt. To make it easier to find things, a group might have more than one parent. For example, the I18n (internationalization) group has two parents, Environment and Editing, as shown in Figure 10-3.
Figure 10-3. Custom's Go to parent group prompt
Choosing Go to parent group is much like choosing Finish but without closing the buffer. It's a useful option if you're just poking around looking for related variables. We'll show you better ways to find particular features to customize later in this chapter.
10.1.3 Customizing with Custom
After you learn your way around, you can tackle customizing Emacs. Each screen of Custom lists variables and other settings. You can edit the value of any variable in the grey text field to the right of variable's name. The current value should be listed. Just delete the current value and type the new value.
Changing a value, however, is not the last step you have to take. You need to save the change before it will take effect. You use the State button to save the change (as mentioned earlier, to save all the values on a page in the same way, you can use the options near the top of the screen). As with other parts of Custom, you can use your mouse or the keyboard. Clicking the left mouse button on State should bring up the list shown in Figure 10-4. Depending on the variable and the change you made (if any), you may or may not have all of the options available.
Figure 10-4. Using the mouse to save or reset an option (Mac OS X)
Of course, you can also activate the State button by placing your cursor on it and pressing Enter. That should create a second window with effectively the same options you get when using the mouse. Figure 10-5 shows the options you see using the Enter key to select State. This list is dynamic, showing only options that are available to you. (It won't show any options if you haven't changed anything yet, but it beeps with an error.)
Figure 10-5. Using the keyboard to save or reset an option (Mac OS X)