Emacs Features: A Laundry List (Unix Power Tools, 3rd Edition)

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19.2. Emacs Features: A Laundry List

Here's the list we promised -- a list of our favorite features:

Emacs is a "windowed editor." Before anyone heard of the X Window System or the Macintosh, Emacs had the ability to divide a terminal's screen into several "windows," allowing you to do different things in each one. You can edit a different file in each window or read mail in one window, answer mail in another, issue shell commands in a third, and so on.

Now that we all have nice workstations with mice and other crawly things for navigating around a bitmapped screen, why do you care? First, you may not have a bitmapped screen, and even if you have one in the office, you may not at home. Second, I still find Emacs preferable to most "modern" window systems because I don't have to use a mouse. If I want to create another window, I just type CTRL-x 2 (which splits the current window, whatever it is, into two); if I want to work in another window, I just type CTRL-x o; if I want to delete a window, I type CTRL-x 0. Is this faster than reaching for my mouse and moving it around? You bet. Particularly since my mouse is hidden under a pile of paper. (Of course, it's hidden because I hardly ever need it.) Once you've created a window, it's just as easy to start editing a new file, initiate a shell session, and so on. Third, even though you're using a windowing system, you may not have a lot of screen real estate available. By having a split Emacs screen, all editing can be done in one window, leaving enough room for other applications, such as the Mozilla web browser, to be open. Whether you're developing web pages or just reading Slashdot while "working," you'll appreciate the free space on the screen. It isn't uncommon for Emacs users to always have Emacs open on their desktops.

Shells

You can start an interactive shell within any Emacs window; just type ESC-x shell, and you'll see your familiar shell prompt. It's easy to see why this is so useful. It's trivial to return to earlier comands, copy them, and edit them. Even more important, you can easily take the output of a command and copy it into a text file that you're editing -- obviously an extremely useful feature when you're writing a book like this. Emacs also lets you issue commands that operate on the contents of a window or a selected region within a window. Another benefit to doing shell work directly in Emacs is that every word that appears in that shell buffer is available for command completions (Section 19.6). So if you're creating a small shell script that has to reference a long directory name, being able to autocomplete that name is an invaluable feature.

In fact, there are many filesystem maintenance tasks with which Emacs can help you. You can view and manipulate directories and files with Dired mode, which can be activated by typing ESC-x dired. You'll be asked which directory you want to view (the current directory is the default). Do you want to remove a file that starts with a hyphen, but rm complains that your file is not a valid option? Start Emacs in Dired mode, select the file, and type D. Emacs will ask you for confirmation about the proposed deletion. Want to delete a bunch of files that can't be easily described with wildcards? In dired mode, select each file with d, then remove them all with ESC-x dired-do-flagged-delete.

Keyboard macros and advanced editing features

Emacs lets you define "keyboard macros" -- and sequences of commands that can be executed automatically. This is similar to vi's map (Section 18.2) facility, with one extra twist: Emacs actually executes the commands while you're defining the macro; vi expects you to figure out what you need to do, type it in without any feedback, and hope that the macro doesn't do anything hostile when you edit it. With Emacs, it's much easier to get the macro right. You can see what it's going to do as you're defining it, and if you make a mistake, you can correct it immediately.

To create a macro, you first need to tell Emacs that it needs to remember the next sequence of keystrokes by typing CTRL-x (. Now perform the desired actions. To end the macro recording, type CTRL-x ). To execute the most recently defined macro, type CTRL-x e. If you make a mistake when recording the marco, type CTRL-g to cancel out of the entire operation, and begin recording the macro again.

Even if you don't create your own macros, Emacs provides a rich set of text- editing features that often do what you mean. For instance, Emacs allows users to make rectangluar text cuts. This is very useful for removing leading whitespace from a series of lines. To make the cut, you must first define the starting point of the rectangle to be cut. Position the cursor in Emacs to the upper-left corner of the area to be excised. Then mark the area with CTRL-SPACE. Move the cursor down to the last line of the area to be removed and then over to right as far as is desired. This is the lowest and rightmost corner of the rectangle. Now remove the area with the key sequence CTRL-x r k.

Editing modes

Emacs has a large number of special editing modes that provide context-sensitive help while you're writing. For example, if you're writing a C program, the C mode will help you to observe conventions for indentation and commenting. It automatically lines up braces for you and tells you when parentheses are unbalanced. In X Windows, Emacs will even do syntax highlighting for you. Perl programmers get two editing modes to choose from, perl-mode and cperl-mode. Based on the file extension, Emacs will figure out which mode you want. (The default and simplest mode is called Fundamental.) You can enter a new mode by typing ESC- x and then the name of the mode. Emacs also integrates well with the perl debugger (ESC-x perldb) so that you can step through your running code in the editor. Emacs also supports many version-control systems including RCS and CVS. Checking out a file from RCS is as simple as typing CTRL-x v v. After you have made your edits, check in the file with CTRL-x v v. That's not a typo; Emacs can figure out the right thing to do with your file because it remembers the last version-control state. Pretty cool. There are special modes for virtually every programming language I've ever heard of. There are also special modes for HTML, troff, T_EX, outlines, stick figures, etc. For any kind of programming, Emacs is the Integrated Development Environment of choice for many users.

Mail, news, FTP, and HTTP

Although I often use Emacs' mail facility as an example, I'm not personally fond of it. However, if you really like working within the Emacs environment, you should try it. Sending mail from Emacs (ESC-x mail) is convenient if you are already editing the file you wish to send. You can simply copy and paste your work into the mail buffer and send it along with CTRL-c CTRL-c. You can even add Cc: and Reply-to: fields to the message just by adding them to the mail buffer directly under the To: field.

Emacs also has a Usenet client called GNUS (ESC-x gnus) that has quite a following. What editor would be complete without an integrated FTP client? Certainly not Emacs. There are two ways to access FTP in Emacs. The first is to type ESC-x ftp. This gives you a shell-like ftp client. While this is nice, Emacs provides an even slicker way to FTP files. Ange-ftp mode allows Emacs users to open remote files almost as if they were local. To open a remote file or directory, simple type CTRL-x CTRL-f. However, you must specify the filename with a leading slash and your remote username followed by @ and followed again by the ftp hostname, a colon, and the full path you wish to retrieve. For example, if I wished to edit the file index.html as user edit on my web server, I would use the filename /[email protected]:/home/html/htdocs/index.html.

To extend the last example a bit, Emacs even has a web-browser mode so that you could look at the web page you just edited! In truth, lynx is still king of the ASCII web browsers, but the Emacs W3 mode is coming along. It doesn't normally come with Emacs, so you're going to have to look on the Web for it. It has very good integration with XEmacs (neè Lucent Emacs) and can even display images. Speaking of the Web, there's a nice Emacs feature called webjump (ESC-x webjumb) that will make a currently opened Web browser such as Netscape go to a new URL. Webjump comes with a list a predefined URLs, which can be expanded, of course. One of those URLs is Yahoo. When that site is selected, webjump will ask you for a query term to submit. After hitting return, the Yahoo search results will appear in a browser window. Again, it's a nice shortcut.

Customization

Emacs is the most customizable tool I've ever seen. Customization is based on the LISP programming language, so you need to learn some LISP before you can work with it much. However, once you know LISP, you can do virtually anything. For example, you could write a complete spreadsheet program within Emacs -- which means that you could use your normal Emacs commands to edit the spreadsheet and incorporate it (in whole or in part) into your documents. In fact, several Emacs spreadsheet modes exist, but their quality and functionality vary wildly. And, because of the FSF's General Public License, virtually all special-purpose packages are available for free.

--ML and JJ


19. GNU Emacs		19.3. Customizations and How to Avoid Them