9.2.1. Firing It Up

$ emacs options

Likewise, XEmacs is invoked as:

$ xemacs options

Most of the time, you don't need options. You can specify filenames on the command line, but it's more straightforward to read them in after starting the program.

In Emacs lingo, C-x means Ctrl-X, and M-p is equivalent to Alt-P. As you might guess, C-M-p means Ctrl-Alt-P.

Using these conventions, press C-x followed by C-f to read in a file or create a new one. The keystrokes display a prompt at the bottom of your screen showing your current working directory. You can create a buffer now to hold what will end up being the content of a new file; let's call the file wibble.txt. We now see the following:

To the right of the buffer type is the word All, which means that you are currently looking at the entire file (which is empty). Typically, you will see a percentage, which represents how far into the file you are.

9.2.2. Simple Editing Commands

Emacs is more straightforward than vi when it comes to basic text editing. The arrow keys should move the cursor around the buffer; if they don't (in case Emacs is not configured for your terminal), use the keys C-p (previous line), C-n (next line), C-f (forward character), and C-b (backward character).

If you find using the Alt key uncomfortable, press Escape and then p. Pressing and releasing Escape is equivalent to holding down Alt.

Find file: /home/loomer/mdw/

where the current directory is displayed. After this, type the name of the file to find. Pressing the Tab key will do filename completion similar to that used in bash and tcsh. For example, entering:

Find file: /home/loomer/mdw/.bash

and pressing Tab opens another buffer, showing all possible completions, as so:

After you complete the filename, the *Completions* buffer goes away and the new file is displayed for editing. This is one example of how Emacs uses temporary buffers to present information.

You can switch to another buffer using the C-x b command, which asks you for the name of the buffer (usually the name of the file within the buffer). For example, pressing C-x b presents the prompt:

Switch to buffer: (default wibble.txt)

The default buffer is the previous one visited. Press Enter to switch to the default buffer, or type another buffer name. Using C-x C-b will present a buffer list (in a buffer of its own), as so:

Popping up the buffer menu splits the Emacs screen into two "windows," which you can switch between using C-x o. More than two concurrent windows are possible as well. In order to view just one window at a time, switch to the appropriate one and press C-x 1. This hides all the other windows, but you can switch to them later using the C-x b command just described. Using C-x k actually deletes a buffer from Emacs's memory.

9.2.3. Tutorial and Online Help

Using the C-h command gives you a list of help options on the last line of the display. Pressing C-h again describes what they are. In particular, C-h followed by t drops you into the Emacs tutorial. It should be self-explanatory, and an interactive tutorial about Emacs tells you more about the system than we can hope to cover here.

File: intercal.info,  Node: Top,  Next: Instructions,  Up: (dir) 
 
   This file documents the Intercal interpreter for Linux. 
 
   * Menu: 
 
   * Instructions::        How to read this manual. 
   * Overview::            Preliminary information. 
   * Examples::            Example Intercal programs and bugs. 
   * Concept Index::       Index of concepts.

As you see, text is presented along with a menu to other "nodes." Pressing m and then entering a node name from the menu will allow you to read that node. You can read nodes sequentially by pressing the spacebar, which jumps to the next node in the document (indicated by the information line at the top of the buffer). Here, the next node is Instructions, which is the first node in the menu.

Each node also has a link to the parent node (Up), which here is (dir), meaning the Info page directory. Pressing u takes you to the parent node. In addition, each node has a link to the previous node, if it exists (in this case, it does not). The p command moves to the previous node. The l command returns you to the node most recently visited.

Within the Info reader, pressing ? gives you a list of commands and pressing h presents you with a short tutorial on using the system. Since you're running Info within Emacs, you can use Emacs commands as well (such as C-x b to switch to another buffer).

If you think that the Info system is arcane and obsolete, please keep in my mind that it was designed to work on all kinds of systems, including those lacking graphics or powerful processing capabilities.

Other online help is available within Emacs. Pressing C-h C-h gives you a list of help options. One of these is C-h k, after which you press a key, and documentation about the function that is bound to that key appears.

9.2.4. Deleting, Copying, and Moving Text

You can set the mark using the key C-@ (or C-Space on most systems). Moving the cursor to a location and pressing C-@ sets the mark at that position. You can now move the cursor to another location within the document, and the region is defined as the text between mark and point.

For example, type the following text into an Emacs buffer:

Now, move the cursor to the beginning of the second line ("Here is a line..."), and set the mark with C-@. Move to the end of the line (with C-e), and delete the region using C-w. The buffer should now look like the following:

In order to yank the text just deleted, move the cursor to the end of the buffer and press C-y. The line should be pasted at the new location:

Pressing C-y repeatedly will insert the text multiple times.

Text that is deleted using other kill commands, such as C-k, is also added to the kill ring. This means that you don't need to set the mark and use C-w to move a block of text; any command that deletes more than one character will do.

In order to recover previously deleted blocks of text (which are saved on the kill ring), use the command M-y after yanking with C-y. M-y replaces the yanked text with the previous block from the kill ring. Pressing M-y repeatedly cycles through the contents of the kill ring. This feature is useful if you wish to move or copy multiple blocks of text.

Emacs also provides a more general register mechanism, similar to that found in vi. Among other things, you can use this feature to save text you want to paste in later. A register has a one-character name; let's use a for this example:

1. At the beginning of the text you want to save, set the mark by pressing the Control key and spacebar together (or if that doesn't work, press C-@).

2. Move point (the cursor) to the end of the region you want to save.

3. Press C-x x followed by the name of the register (a in this case).

4. When you want to paste the text somewhere, press C-x g followed by the name of the register, a.

9.2.5. Searching and Replacing

To replace a string, enter M-%. You are prompted for the string that is currently in the buffer, and then the one with which you want to replace it. Emacs displays each place in the buffer where the string is and asks you if you want to replace this occurrence. Press the spacebar to replace the string, the Delete key to skip this string, or a period to stop the search.

If you know you want to replace all occurrences of a string that follow your current place in the buffer, without being queried for each one, enter M-x replace-string. (The M-x key allows you to enter the name of an Emacs function and execute it, without use of a key binding. Many Emacs functions are available only via M-x, unless you bind them to keys yourself.) A regular expression can be replaced by entering M-x replace-regexp.

9.2.6. Macros

Here's a example you can try on any text file; it capitalizes the first word of each line.

1. Press C-x ( to begin the macro.

2. Press C-a to put point at the beginning of the current line. It's important to know where you are each time a macro executes. By pressing C-a you are making sure the macro will always go to the beginning of the line, which is where you want to be.

3. Press M-c to make the first letter of the first word a capital letter.

4. Press C-a again to return to the beginning of the line and C-n or the down arrow to go to the beginning of the following line. This ensures that the macro will start execution at the right place next time.

5. Press C-x ) to end the macro.

6. Press C-x e repeatedly to capitalize the following lines. Or press C-u several times, followed by C-x e. The repeated uses of C-u are prefix keys, causing the following command to execute many times. If you get to the end of the document while the macro is still executing, no harm is done; Emacs just beeps and stops executing the macro.

9.2.7. Running Commands and Programming within Emacs

Simply enter your message within this buffer and use C-c C-s to send it. You can also insert text from other buffers, extend the interface with your own Emacs LISP functions, and so on. Furthermore, an Emacs mode called RMAIL lets you read your electronic mail right within Emacs, but we won't discuss it here because most people prefer standalone mailers. (Usually, these mailers let you choose Emacs as your editor for email messages.)

GNUS is an example of the power of using Emacs interfaces to other tools. You get all the convenience of Emacs's navigation, search, and macro capabilities, along with specific key sequences appropriate for the tool you're using.

Using the arrow keys, you can select a newsgroup to read. Press the spacebar to begin reading articles from that group. Two buffers will be displayed, one containing a list of articles and the other displaying the current article.

Using n and p move to the next and previous articles, respectively. Then use f and F to post a follow-up to the current article (either including or excluding the current article), and r and R to reply to the article via electronic mail. There are many other GNUS commands; use C-h m to get a list of them. If you're used to a newsreader, such as rn, GNUS will be somewhat familiar.

cd /home/loomer/mdw/pgmseq/ 
make -k 
gcc -O -O2 -I. -I../include -c stream_load.c -o stream_load.o 
stream_load.c:217: syntax error before 'struct' 
stream_load.c:217: parse error before 'struct'

You can move the cursor to a line containing an error message and press C-c C-c to make the cursor jump to that line in the corresponding source buffer. Emacs opens a buffer for the appropriate source file if one does not already exist. Now you can edit and compile programs entirely within Emacs.

9.2.8. Tailoring Emacs

; C-c followed by s will put buffer into SGML mode."
(global-set-key "\C-cs" 'sgml-mode)

; Make text mode the default, with auto-fill
(setq default-major-mode 'text-mode)
(add-hook 'text-mode-hook 'turn-on-auto-fill)

You don't always want your key mappings to be global. As you use T_EX mode, C mode, and other modes defined by Emacs, you'll find useful things you'd like to do only in a single mode. Here, we define a simple LISP function to insert some characters into C code, and then bind the function to a key for our convenience:

(defun start-if-block( ) 
  (interactive) 
  (insert "if ( ) {\n}\n") 
  (backward-char 6) 
)

We start the function by declaring it "interactive" so that we can invoke it (otherwise, it would be used only internally by other functions). Then we use the insert function to put the following characters into our C buffer:

if ( ) { 
}

Strings in Emacs can contain standard C escape characters. Here, we've used \n for a newline.

Now we have a template for an if block. To put on the ribbon and the bow, our function also moves backward six characters so that point is within the parentheses, and we can immediately start typing an expression.

Our whole goal was to make it easy to insert these characters, so now let's bind our function to a key:

(define-key c-mode-map "\C-ci" 'start-if-block)

If you'd like to write your own Emacs LISP functions, you should read the Info pages for elisp, which should be available on your system. Two good books on writing Emacs LISP functions are An Introduction to Programming in Emacs Lisp, by Robert J. Chassell (GNU Press) and Writing GNU Emacs Extensions, by Bob Glickstein (O'Reilly).

(keyboard-translate ?\C-h ?\C-?)

Pretty cryptic code. \C-h is recognizable as the Control key pressed with h, which happens to produce the same ASCII code (8) as the Backspace key. \C-? represents the Delete key (ASCII code 127). Don't confuse this question mark with the question marks that precede each backslash. ?\C-h means "the ASCII code corresponding to \C-h." You could just as well specify 8 directly.

So now, both Backspace and C-h will delete. You've lost your help key. Therefore, another good customization would be to bind another key to C-h. Let's use C-\, which isn't used often for anything else. You have to double the backslash when you specify it as a key:

(keyboard-translate ?\C-\\ ?\C-h)

There are other key bindings you may want to use. For example, you may prefer to use the keys C-f and C-b to scroll forward (or backward) one page at a time, as in vi. In your .emacs file you might include the following lines:

(global-set-key "\C-f" 'scroll-up) 
(global-set-key "\C-b" 'scroll-down)

You can create your own prefix keys, if you really want to extend your current mode with lots of new commands. Use something like:

(global-unset-key "\C-d") 
(global-set-key "\C-d\C-f" 'my-function)

First, we must unbind the C-d key (which simply deletes the character under the cursor) in order to use it as a prefix for other keys. Now, pressing C-d C-f will execute my-function.

; Default mode for editing text 
(setq default-major-mode 'indented-text-mode)

You should also rebind the Enter key to indent the next line of text:

(define-key indented-text-mode-map "\C-m" 'newline-and-indent)

; Toggle overwrite mode. 
(global-set-key "\C-r" 'overwrite-mode)

(setq text-mode-hook 'turn-on-auto-fill) 
(setq fill-column 72)

9.2.9. Regular Expressions

Even a few regular expression tricks can vastly increase your power to search for text and alter it in bulk. Regular expressions were associated only with Unix tools and languages for a long time; now they are popping up in other environments, such as Microsoft's .NET, but only Unix offers them in a wide variety of places, such as text editors and the grep command where ordinary users can exploit them.

Let's suppose you're looking through a file that contains mail messages. You're on a bunch of mailing lists with names, such as gyro-news and gyro-talk, so you're looking for Subject lines with gyro- in them. You can use your text editor or the grep command to search for:

^Subject:.*gyro-

Figure 9-1. Simple regular expression

Figure 9-2. Regular expression with more parts

Brackets, like carets and asterisks, are special characters in regular expressions. Brackets are used to mark whole classes of characters you want to search for, such as [a-z] to represent "any lowercase character." We don't want the bracket before gyro to have this special meaning, so we put a backslash in front of it; this is called escaping the bracket. (In other words, we let the bracket escape being considered a metacharacter in the regular expression.)

The first asterisk in our expression follows a space, so it means "match any number of spaces in succession." The second asterisk follows the [a-z] character class, so it applies to that entire construct. By itself, [a-z] matches one and only one lowercase letter. Together, [a-z]* means "match any number of lowercase letters in succession."

A sophisticated use of regular expressions can take weeks to learn, and readers who want to base applications on regular expressions would do well to read Mastering Regular Expressions, by Jeffrey Friedl (O'Reilly).