Type: In M-/
Emacs inserts the last word starting with in, in this case, interesting.
Interesting was not the word we were hoping for; it's invertebrates we wanted. Without moving the cursor, type M-/ again.
Type: M-/
Emacs inserts the word Invertebrates, which is what we wanted.
The word being expanded need not be earlier in the file to be considered nearest. Emacs looks behind and ahead of the cursor position to find words it can expand. If there are eligible words that are equidistant above and below the cursor position both, Emacs selects the word that is above as the expansion.
Earlier we talked about completing a word with Ispell. Dynamic abbreviations are a bit different. When you complete a word, the word probably isn't in the buffer (yet). When you use a dynamic abbreviation, you simply don't want to type a word you typed earlier and you're asking Emacs to do it for you.
Using dynamic abbreviations doesn't require entering a special minor mode, as standard word abbreviations do. They are simply an aid for the tired typist. Word abbreviation mode has some other advantages, though, such as the ability to create an abbreviation for a phrase or a habitual typo, as we will see next.
3.4.2 Word Abbreviation Mode
Word abbreviation mode lets you define abbreviations for special words and phrases. You can use it in many ways. Traditionally, abbreviation mode is used so that you don't have to type long words or phrases in their entirety. For example, let's say you are writing a contract that repeatedly references the National Institute of Standards and Technology, and you are not allowed to use an acronym. Rather than typing the full name, you can define the abbreviation nist. Once you have set up this definition, Emacs inserts the full name whenever you type the abbreviation nist, followed by a space, tab, or punctuation mark. Emacs watches for you to type an abbreviation, then expands it automatically for you.
Before showing you how to get into word abbreviation mode and define your abbreviation list, we'll start with an example. Our favorite nontraditional use for word abbreviation mode is to correct misspellings as you type.[21] Almost everyone has a dozen or so words that they habitually type incorrectly because of worn neural pathways. You can simply tell Emacs that these misspellings are "abbreviations" for the correct versions, and Emacs fixes the misspellings every time you type them; you may not even notice that you typed the word wrong before Emacs fixes it. So assume that you've entered word abbreviation mode, and that you've defined receive as an abbreviation for recieve; now, as you're typing, you make an innocent mistake.
Type: You will recieve
You type the offending word but haven't yet pressed Space, which will cue Emacs to correct it (Windows).
Type: Space the materials you requested shortly
Emacs corrects the word automatically after you press Space; you need not stop typing or even be aware that a mistake has been made and corrected (Windows).
Besides the convenience of being able to invent abbreviations for phrases that you frequently type, you can see that setting up a short list of abbreviations for common misspellings could reduce the time it takes to proofread files and reduce the number of common typing errors.
When you define abbreviations, never use abbreviations that are words in their own right or Emacs may expand the word when you don't want it to, because expansion takes place without asking. For example, if you frequently write about the World Association for Replicant Technology, don't define an abbreviation of wart, or you won't be able to write about the difficulties of handling toads. (If you use the word wart so infrequently that you think the convenience of the acronym warrants it, you can use C-_ to undo the abbreviation when you really want to type wart.)
Emacs knows the abbreviations exactly as you define them. If you define recieve as an abbreviation for receive, you must also define recieves, recieving, and recieved as abbreviations to cover all the forms of the word you might misspell.
Before you go ahead and define some abbreviations, here's one more basic fact you should know. Emacs classifies abbreviations according to which modes they work in. Global abbreviations work in all modes; local abbreviations work only in the mode in which they were defined. For example, if you want abbreviations to work only in text mode and not in C mode, define them as local while you are in text mode. If you want abbreviations to work in any mode, define them as global. Remember: abbreviations are local to modes, not to files or buffers.
Emacs also provides an inverse method for defining abbreviations. This method is called inverse because you type the abbreviation and then the definition. Some commands (which we won't discuss) let you type the definition and then the abbreviation, but they require some tricky key sequences to let Emacs know how many words preceding the cursor are part of the abbreviation. The inverse method is easier and it works whether the definition for the abbreviation is one word or ten words.
3.4.2.1 Trying word abbreviations for one session
Usually, if you go to the trouble of defining a word abbreviation, you will use it in more than one Emacs session. But if you'd like to try out abbreviation mode to see if you want to incorporate it into your startup, use the following procedure.
To define word abbreviations for this buffer and session:
1. Enter word abbreviation mode by typing M-x abbrev-mode Enter. Abbrev appears on the mode line. For a global abbreviation, type the abbreviation you want to use and type C-x a i g or C-x a - (for add-inverse-global). (For a local abbreviation, type C-x a i l for add-inverse-local instead.) Emacs then asks you for the expansion.
2. Type the definition for the abbreviation and press Enter. Emacs then expands the abbreviation and will do so each time you type it followed by a space or punctuation mark.
3. When you exit Emacs. it asks if you want to save the abbreviations in .abbrev_defs. Type y if you want to save them.
4. The abbreviations you've defined will work only in buffers where you enter abbrev mode.
If you find that you like using word abbreviation mode, you may want to make it part of your startup, as described in the following section.
3.4.2.2 Making word abbreviations part of your startup
Once you become hooked on using abbreviation mode, it's easiest to incorporate it into your .emacs file. This procedure creates a permanent file of your word abbreviations that is loaded every time you start Emacs. You can also delete abbreviations from this file; we'll discuss how to do so in the next section.
21
Once upon a time this use of word abbreviation mode was nontraditional; these days Flyspell, described earlier, automatically defines misspellings as abbreviations.