If you use the default bindings (rather than CUA mode), you may use C-x u for undo.[19] (Undo is such a common command that it's easy to type C-x C-u by mistake when you undo repeatedly. Unfortunately, C-x C-u is a disabled command for upcase-region. If you type C-x C-u, an annoying message about enabling the command pops up.
If you don't anticipate a big need for upcasing regions, you can redefine C-x C-u so that it also runs undo. To do so, add this line to your .emacs file:
(define-key global-map "\C-x\C-u" 'undo)
After making this change, typing C-x C-u runs undo, just as C-x u does.
Emacs customization is extremely powerful, and you can make Emacs work just the way you want it to. A far more extensive treatment of customization is found in Chapter 10. This brief introduction is meant to whet your appetite and to make it possible for you to add lines to your .emacs file as we mention potential customizations throughout the book.
The next chapter covers topics such as the many searches offered by Emacs, including query-replace, as well as spell checking and word abbreviation mode (often used to correct typos automatically). If you want to learn about these features, go on to the next chapter. From here on, you can take a selective approach to reading this book, picking and choosing whatever you want to learn about; you don't need to read the rest of the book sequentially.
2.7.5 Problems You May Encounter
• You get an error message when you start Emacs after changing the .emacs file. The message appears only briefly; press M-p to view it again. Edit your .emacs file, checking the lines you added carefully against their source for minor typographical errors. Something as simple as a missing hyphen or apostrophe can cause this error. Fix the error, save the file, exit Emacs, and reenter. In extreme cases (the .emacs file is so messed up that Emacs won't even let you edit it), exit Emacs, rename the .emacs file, and then start Emacs and edit it again to fix it. Rename it back to .emacs and start again.
• Paragraphs are not reformatted properly. This seems to relate to window size. Try resizing the window horizontally until paragraphs format properly.
Chapter 3. Search and Replace
The commands we discussed in the first two chapters are enough to get you started, but they're certainly not enough to do any serious editing. If you're using Emacs for anything longer than a few paragraphs, you'll want the support this chapter describes. In this chapter, we cover the various ways that Emacs lets you search for and replace text. Emacs provides the traditional search and replace facilities you would expect in any editor; it also provides several important variants, including incremental searches, regular expression searches, and query-replace. We also cover spell-checking here, because it is a type of replacement (errors are sought and replaced with corrections). Finally, we cover word abbreviation mode; this feature is a type of automatic replacement that can be a real timesaver.
3.1 Different Kinds of Searches
While you're editing, you frequently want to find something you've already typed. Rather than hunt through the file trying to find what you're looking for, virtually all editors provide some kind of search feature that lets you look for a particular text string. Emacs is no exception to the rule. It supplies a search command—in fact, it provides a dizzying array of search commands. Here's a quick summary of the different kinds of searches that are available:
Simple search
You give Emacs a search string, and it finds the next occurrence. You will find this search in almost any editor.
Incremental search
With incremental search, Emacs starts to search the file as soon as you type the first character of a search string. It continues to search as you type more characters.
Word search
A word search is like a simple search, except that Emacs searches only for full words and phrases. For example, if you are searching for the word hat, you don't have to worry about finding the word that. A word search is also useful when you need to find a phrase that is spread across two lines.
Regular expression search
To search for patterns, you can use a regular expression search. For example, if you wanted to find all instances of B1 and B2, you could search for them using the regular expression B[12]. However, regular expressions can be extremely complex. We'll give a brief introduction to this topic here; it is discussed more fully in Chapter 11.
Incremental regular expression search
This search procedure is a combination of an incremental search and a regular expression search.
You can search forward or backward. Searches can be either case-sensitive, meaning that Emacs considers upper- and lowercase letters to be different (i.e., the words This and this are different) or case-insensitive, in which upper- and lowercase are not differentiated (i.e., This and this are equivalent). By default, searches are case-insensitive, with upper- and lowercase letters considered to be the same. One exception: if you type any uppercase letters, Emacs makes the whole search string case-sensitive; it assumes you are looking for something precise since you've made the extra effort to type some letters in uppercase.
Replacement operations are closely related to searches. As with searches, Emacs offers you several different flavors:
Simple search and replace
In this procedure, Emacs replaces all occurrences of one string with another. Usually, this is too radical a solution and can have unintended results. Try query-replace instead.
Query-replace
With query-replace, Emacs conditionally replaces a string throughout a file. Emacs finds all occurrences of the search string, and for each one it asks you whether or not to perform the replacement. This type of replacement is useful if you need to change some, but not all, instances of a word or phrase throughout a file.
Regular expression replace
Regular expression replacement uses the powerful pattern matching facility of the same name to find strings and replace them.
So now you know what you'll be looking at. Don't be intimidated by the wealth of searches that are available. In practice, you'll probably settle on one search command and one replace command and use these for 99 percent of your work. For example, we use incremental search and query-replace most of the time. If you're a writer, you may use word search all the time; if you're a programmer, you might want a regular expression search. If you're just beginning, you may want to learn incremental search and read the rest of this chapter later. However, if you know what's available, you'll be able to make use of the other search commands when they become useful.
19
You could use C-_ for undo instead and then you wouldn't need to read this section. We recommend that you read it anyway because you might find another annoying key mapping that you want to change and this section tells a bit about how to do so.