Text files and editors: emacs and xemacs

The emacs editor, and its cousin xemacs, are powerful text editors which have many extensions to help users edit specific types of file. Unlike vi they do not have different command and edit modes, and anything you type will appear in the document.

In order to enter commands, you will need to use one of two special keys. The first is the `control key', usually found on the bottom left and right of your keyboard and marked with the letters `Ctrl'. We will use the `CTRL' to refer to this key, so for example `CTRL-x' will mean hold down the control key and press x. Linux sometimes uses `$\land$' to refer to the CTRL key, and Emacs itself uses `C' to refer to the control key (though this can get confusing since `C' is quite a common letter!).

The second special key is called the meta-key, and on PCs this is usually the alternate key, marked `Alt' on most keyboards and found next to the spacebar. On some computers they use the escape key as the meta-key instead (marked `Esc' and found on the top-left of the keyboard). Emacs denotes this key `M', we will simply use `ALT', though remember that this might be the escape key instead.

You can have several files open in emacs at once, and emacs refers to these as `buffers'. A buffer is an area of memory the computer sets aside to store something for easy access.

Probably the most important things you need to know to use emacs are:

• Moving the cursor one space
  You can also move the cursor with the arrow keys.
• Moving the cursor one word
  You can move the cursor one word right or left by holding down the control key as you press the right or left arrow key.
• Moving the cursor one paragraph
  You can move the cursor one paragraph up or down by holding down the control key as you press the up or down arrow key.
• Deleting a character
  The delete key usually deletes the character under the cursor, whereas the backspace key usually deletes the character to the left of the cursor and moves the cursor one space to the left.
• Deleting a word
  Holding down the control key and pressing delete deletes from the cursor to the right end of the word, whereas backspace key usually deletes the character to the left of the cursor and moves the cursor one space to the left.
• Deleting a line
  CTRL-k kills (deletes) the text of a line without removing the line itself, CTRL-k again will remove the line. In fact the line is not gone forever, it is stored in a `kill buffer'.
• Pasting text
  CTRL-y brings back (`yanks') whatever was last stored in the kill buffer.
• Defining a region
  CTRL-SPACE tells emacs to remember the current cursor position and use it to define the start of a region of text.
• Cutting a region
  Once you have marked the start of a region of text (see above) you can move the cursor somewhere else and then use CTRL-w to cut everything between the current cursor position and the start of the region. The text is placed into the kill buffer.
• Copying a region
  As for cutting, but use ALT-w instead of the control key. The text is placed into the kill buffer, but not removed from its current location.
• Searching for a string
  Type CTRL-s, and you will see the text `I-search:' appear at the bottom of the window. Type the text you want to search for - the search is carried out as you type. CTRL-s again will take you to the next occurence.
• Undo a change
  To undo the last change use CTRL-_ where `_' is the underscore character usually found by holding down the shift key and pressing the `-' button. Repeating this will undo the change before that, and so on.
• Saving a file
  CTRL-x CTRL-s saves the current file, i.e. you hold down the control key and press x, then hold down the control key again and press s (in fact you could just keep the control key pressed down the whole time).
• Saving a file under a different name
  CTRL-x CTRL-w will prompt you for a new path and filename to save the current buffer to. Simply type what you want and press the enter key.
• Quitting emacs
  CTRL-x CTRL-c quits emacs. If you haven't written the file to disk since your last changes it will warn you and ask what you want to do. Press `y' to save the changes, 'n' not to, or 'q' to forget about quitting altogether. If you have chosen not to save changes emacs will warn you once more and ask whether you really want to quit. This time you must type either `yes' or `no'.

There are many more emacs commands, and in fact it will do far more than just text editing. The easiest way to get into emacs is to use xemacs which has a set of handy menus at the top and tells you what the equivalent keystrokes are. There are many good resources on the internet for learning emacs.