Section 10: Editing Text with EMACS
One of the most basic operations you will need to perform on a UNIX
system is text editing. Whether you are preparing a document, writing
a program, or sending email to a colleague, you will need a utility to
allow you to enter and edit text.
There are many editors available for UNIX systems, but this discussion
will focus on the emacs text editing program because of its
power, flexibility, extensibility, customizability, and prevalence.
No matter where you get a UNIX account, you are likely to have emacs
at your disposal.
Here is an index to the topics in this section:
General features of the emacs editor
Emacs is a visual editor. That means that you have a representation
of your entire document on your screen, and you can move around
freely, editing any part of the document you wish. Older editors,
referred to as line editors, required all changes to the file
to be made on a line-by-line basis. Each command to a line editor
specified a line number, and the changes to be applied to that line.
Line editors are truly horrible things, and you should feel lucky if
you have never seen one.
Emacs uses control and escape characters to distinguish editor
commands from text to be inserted in the buffer. In this document,
the notation "Control-X" means to hold down the control key, and
type the letter x. You don't need to capitalize the x, or any other
control character, by holding down the shift key. "ESCAPE-X" means
to press the escape key down, release it, and then type x.
Working with buffers
When you edit a file in emacs, you're not really editing the file
itself, as it sits out on a disk somewhere. Instead, emacs makes a
copy of the file, and stores the copy in a part of RAM memory called a
buffer. All the changes you make to the file are applied to the
buffer. When you save the file, emacs writes the contents of the
buffer to the disk.
Because the buffer exists in RAM memory, it disappears if the power is
turned off, or if the system crashes. Thus, you should use the save
command often, flushing your current buffer to disk. Once the file is
on disk, a power outage or system crash shouldn't harm it.
Basic operations in emacs
Here are some of the fundamental things you'll need to do when you
edit a document in emacs.
To start emacs, just type the command
the UNIX shell. If you want emacs to start with a file already loaded
into a buffer, type
"filename" is the name of the file you want to edit.
- emacs filename
To exit emacs and return to the UNIX shell, type Control-X-Control-C.
If you have made changes to the buffer since the last time you saved
it to disk, emacs will ask you if you want to save. Type y for yes,
or n for no.
Emacs has an on-line help system that can be invoked by typing
Control-H. If you type the question mark (?), emacs will present a
list of help topics you can choose.
The emacs display
The display in emacs is divided into three basic areas. The top area
is called the text window. The text window takes up most of
the screen, and is where the document being edited appears. At the
bottom of the text window, there is a single mode line. The
mode line gives information about the document, and about the emacs
session. The bottom line of the emacs display is called the
minibuffer. The minibuffer holds space for commands that you
give to emacs, and displays status information.
Aborting a command
You can abort an emacs control or escape sequence by typing the
Working with files
To read a disk file into an emacs buffer, type the command
Control-X-Control-F. Emacs will ask you for the name of the file. As
you type the name of the file, it will be displayed in the minibuffer.
When you have entered the file name, press the return key, and emacs
will load the file into a buffer, and display it in the text window.
The command to save the contents of the buffer to a disk file is
Control-X-Control-S. The save command overwrites the old version of
the file. You may also write the contents of the buffer to a
different file with the command Control-X-Control-W. Emacs will
prompt you for the name of the file you want to create.
To create a new file, use Control-X-Control-F, just as if the file
already existed. When emacs asks you for the file name, type in the
name you want your new file to have, and emacs will create the file,
and display an empty buffer for you to type in.
Emacs will perform file name completion for you. Type part of the
name of the file you want, and press the spacebar or tab key to get
emacs to complete a file name. If the partial name you've given
matches more than one file, emacs will display a list of all potential
matches. You can continue typing in more of the file's name, and
pressing either file completion key, until you zero in on the file you
On well-configured systems, you will find that the keyboard arrow keys
will function correctly in emacs, moving you forward or backward one
character at a time, and up or down one line at a time. If the arrow
keys do not work, here's how to accomplish the same functions:
- Control-F moves the cursor forward to the next character.
- Control-B moves the cursor back to the previous character.
- Control-N moves the cursor to the next line.
- Control-P moves the cursor to the previous line.
In addition to basic cursor motion, emacs provides some other handy
cursor motion functions:
- Control-A moves the cursor to the start of the current line.
- Control-E moves the cursor to the end of the current line.
- ESCAPE-F moves the cursor forward to the next word.
- ESCAPE-B moves the cursor back to the previous word.
- ESCAPE-< moves the cursor to the start of the buffer.
- ESCAPE-> moves the cursor to the end of the buffer.
Inserting and deleting text
To insert text into a buffer, place the cursor where you want to start
inserting text, and start typing away.
If you want to insert the contents of another file into the current
buffer, place the cursor at the desired insertion point, and type
Control-X-I. Emacs will ask you for the name of the file you wish to
You may also insert text by cutting it from one place, and pasting it
at the insertion point. See the next section for information on
cutting and pasting.
Deleting text is easy. As you'd expect, the delete key deletes
backward one character. Here are some other ways to delete text:
- Control-D deletes forward one letter.
- Control-K deletes from the point to the end of the line.
- ESCAPE-D deletes forward one word.
- ESCAPE-delete deletes backward one word.
Cutting and pasting text regions
Emacs allows you to select a region of text, and perform cut and paste
operations on the region. It uses a temporary storage area called the
"kill buffer" to allow you to store and retrieve blocks of text.
There is only one kill buffer in emacs, which means that you can cut
text from one document, and paste it into another.
To define a region of text, place the cursor at one end of the region
and press Control-spacebar. That sets the mark. Then, move the
cursor to the other end of the region. The text between the mark and
the cursor defines the region.
To cut a region of text, and place it in the kill buffer, use the
command Control-W (think of Wipe).
The paste command is Control-Y. It Yanks the block of text
from the kill buffer, and places it where the cursor rests. The
Control-Y command only retrieves the most recently-cut block of text.
You can paste in earlier cuts by pressing ESCAPE-Y. The ESCAPE-Y
command, used repeatedly, will take you back through several previous
text blocks that were cut. The ESCAPE-Y command does not work unless
you type Control-Y first.
You may copy a region of text into the kill buffer without cutting it.
Define the text block by setting the mark at one end, and moving the
cursor to the other end. Then type ESCAPE-W.
It is possible to undo the changes you have made to a file by entering
the command Control-_. (That's Control-underscore. On some keyboards,
you'll have to hold down both the control and shift keys to enter the
Many word processing programs can only undo the most recent command,
but emacs remembers a long history of commands, allowing you to undo
many changes by repeatedly entering the Control-_ code.