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EMACS is an advanced, self-documenting,
customizable and extensible editor.
EMACS is advanced
because it provides facilities beyond that of a standard
editor. EMACS can do more than just insertions, deletions and
one-character manipulations. Functions such as: filling of text,
automatic indentation, viewing multiple files at once, and the concept
of dealing with text in terms of ``words'', ``lines'', ``paragraphs''
and ``sentences'' instead of just ``characters'' make it very powerful
and useful.
EMACS is self-documenting because at any
time you can type a help command and get help on EMACS, specific
commands, a particular key, or even execute an on-line
tutorial program.
EMACS is customizable because you can define keys to perform
functions to suit your own needs (called Key-Bindings), or you may
choose to actually change the way built-in functions behave.
EMACS is extensible
because new commands can be added to it very
easily without changing the rest of it. There are also many extensions
available to make programming, text processing and even reading
mail easier by having EMACS do much of the work for you (such as
parenthesis matching, automatic ``pretty printing'' for programs, and
special modes for TeXand LaTeX).
EMACS is available on most Unix systems. ALL of the RCF machines run the same version of GNU EMACS. Even though implementations may be slightly different, the user can always customize it to their own preferences.
This next section will introduce a few of the concepts that make Emacs manageable. Keep in mind that EMACS is a text editor, not a word processor.
A buffer is the basic ``holding area'' for EMACS. When you edit a file, what actually happens is that EMACS will read the contents of the file into a buffer and give it the same name as the file. This is a very important concept to understand, because the contents of the file will NOT be changed until you give EMACS the command to write the buffer back out. In general, EMACS is very good about telling you when you have forgotten to write out the contents of a buffer you have changed before it lets you exit. Buffers can be associated with files, shells (you can actually run system commands from within EMACS), and EMACS functions (such as HELP). There is no practical limit to the number of buffers that you can use, and it is very easy to switch between them.
A window is a piece of the screen that displays a buffer. You can have more than one window on the screen at once. You can have multiple windows each displaying different sections of a single buffer. In practical use, you can look at two (or more) files at once, or two (or more) places in the same file at once, and move text between them. The number of windows you can have on the screen at once is only limited by the number of lines on the display.
At the bottom of the screen you will see the mode-line displayed in either reverse-video, or bold-face depending on the terminal type. This line shows you that you are in EMACS. This is followed by the name of the buffer that you are in, the ``mode'' of EMACS that you are using, and your position in the text. When you create a new file you will be looking at a blank screen. The position field will say -ALL- because you are looking at all of the screen. When the buffer is larger than one screen, the position field will be expressed as either -TOP- (if you are at the beginning), -BOTTOM- (if you are at the end), or a percentage of how far you are into the text (if you are somewhere in the middle). This mode-line line is very useful. If you look carefully, you will notice that on the left of the line there are some dashes and asterisks. These signify the status of the buffer. If this part of the line looks like ``- - * * -Emacs:'' then you have a modified-buffer and it needs to be saved. If this part is all dashes ``- - - - -Emacs:'' then no changes have been made since the last time the buffer was saved. If you want to edit two files at once, you can have them both up on the screen simultaneously in separate windows, and each window will have its own mode-line.
Most EMACS commands are entered by using one or two keystrokes. If you are in an RCF lab or logged in remotely by ssh, you can use the default function keypads for most purposes. A copy of these keypad definitions is available from the RCF staff. It is worthwhile to learn how to use the keypads because it will save you a lot of time and typing. To enter commands NOT included on the keypad, use either control-sequences or the minibuffer. The three basic command prefixes are:
Ctrl Key while hitting the next key''. For example: The command for
transposing two characters is transpose-chars, or the keystroke
C-t. This means ``Hold down the Ctrl key and press
t. This will cause the transpose-chars command to be executed.
Meta - (M- ) which means ``Press Meta key before
hitting the next character''. By default the Meta key is
ESC (The escape key, which is F11 on VT-220 terminals, and ESC on the
Esprit and most other terminals). In most cases, Alt can work as ths
Meta key as well.
For example: The command to transpose two
words is transpose-words, or the keystroke M-t. This
means ``Press the Meta key (which is ESC) then press
t. This will cause the transpose-words command to be executed.
press x''. This tells EMACS to run a command by name. When you
enter this, EMACS will ask you to fill in the command name at the
bottom of the screen. This part of the screen is called the
minibuffer. After you have entered the command, press the
(RETURN) key to execute it. For example: Another way to run
the transpose-words command would be to enter the command
M-x transpose-words . This would be done by pressing
M-x (press ESC, and then press x). Then type
transpose-words , and the command will be
executed.
To start up EMACS, simply type emacs at the system command prompt. If you wish to create a new file, or edit an existing file, you may include the name of that file on the command line. The following example will start EMACS and edit the file testfile.
% emacs testfile
After this is done, the screen will clear and the cursor will be in the top-left corner of the screen.
Once EMACS is started, you may begin editing. If you are creating a
new file, the buffer will be empty and you can begin typing out
your text. If you do not give EMACS a filename when it is started,
you will be in a buffer named *scratch*. The section on
Reading and Saving Files describes the command for reading in a file
after EMACS is started. By default, EMACS will do automatic
``line-wrapping'' so that you do not have to press a
at the end of each line.
The easiest way to move around a document is to use the next-line, previous-line, forward-character and backward-character functions to move one line or character at a time. Since this can get a little tedious in a large document, you can also move by word, by line, by sentence, by paragraph or by screen. The VT-series and Esprit keypad diagrams show how the function keys on these terminals are bound by default.
In EMACS, you use a mark and a point to delimit specific regions of text for killing (deleting), moving, copying, saving, or indenting. The mark is an invisible pointer that you set at the beginning of a region by using the set-mark command. The point is always located to the left of the current cursor position.
If you only need to do small deletions, you can use the delete-previous-character and delete-next-character functions. There are also the delete-previous-word and delete-next-word commands for deleting words and the kill-from-start-of-line and kill-to-end-of-line commands for deleting lines. If you need to delete large sections of text or want to move large amounts of text, you should use the set-mark, kill-region and yank functions as follows:
a mark in the text at the position where you want to begin text between the mark and the point (to the left of where the cursor is). If you are only deleting text then you are done. If you want to move this region somewhere else, then do the next two text inserted. This can be anywhere in the buffer, or you can switch killed and inserts it at the current point.
(C-x C-f) This command will prompt for a file name, create a new buffer with the same name as the file, and then read that file into When you save a buffer, EMACS will use the current buffer name (C-x C-w) This command will ask you to give it a filename, then save the current buffer into that file.
There is a way to undo commands in EMACS. undo (C-x u) undoes the last command. Consecutive repetitions of undo will undo earlier and earlier changes. The limit to the number of changes that you can undo varies depending on the complexity of the previous commands, but it is more than sufficient for most purposes.
Another useful command is revert-buffer (M-x revert-buffer). This command will revert the state of the current buffer back to its original contents. This command will only work on buffers that were loaded from files. When you revert-buffer the buffer will be re-loaded from disk with the previous version of the file.
Another problem that may be encountered occurs when EMACS is aborted abnormally. If the system crashes while you are in an editing session, your work is not lost. When you edit a file from a session that was abnormally aborted, EMACS will send a message to the minibuffer telling you to use the recover-file command. When you invoke the recover-file command (M-x recover-file), your last editing session will be ``replayed'' on the screen. This will restore as much of the lost session as possible.
If you make an error entering a command, or want to stop EMACS in the middle of a command, use abort (C-g). This command will abort a partially typed command, or a command that is currently executing.
You can leave EMACS in two different ways:
save-buffers-kill-emacs - (C-x C-c) This command will
automatically ask you if you want to save any modified buffers before
exiting EMACS. Answer yes or no when it asks you about
- (C-z) This command will suspend the current EMACS process
in the current state. You may re-attach to it by using a shell command
such as %emacs in the C-shell.
At the beginning of this document we said that EMACS was self-documenting. There are a variety of help facilities available within EMACS. The main help functions and keystrokes to invoke them are:
help facility with no options. This will ask you for an
documentation browsing system. This system will allow you to
look at ALL of the EMACS documentation files. The complete
takes you through all of the basic features of EMACS. This is
a ``learn-by-doing'' style of tutorial. It is very easy to
sophisticated way of getting help. A possible question one
might have would be: ``What are
the commands for working with files ?'' To answer this,
use the command (C-h a file ). This will
list out all of the commands that contain the word file.
Copies of the GNU-EMACS manual are available from the RCF, however this manual can be accessed on-line via the info system as described above.
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