An Introduction to Unix

3.4. The Mark and the Region

emacs has a number of commands that work on an entire block of text at a time. For example, the emacs tutorial told you how to delete a line using C-k. But what if you wanted to delete everything from the middle of one line to the 1st word five lines away? There is a command (C-w) for killing an entire region of text, but to use it you must first tell emacswhat region you want to kill.

The procedure for doing this is the same in all emacs commands that work on regions of text. The “current region” is the set of characters from the “mark” to the current cursor position. The “mark” is an imaginary position marker established by the set-mark-command. The keystrokes for that command are either C-[spc] (hold the control key and type a space) or C-@ (hold the control and shift keys and type '2').22

Some telnet programs (notably, the MS Windows built-in telnet) will not let you type the characters C-[spc] or C-@. These characters are the emacs keys used to set the “mark” when selecting a region of text.

You can always run the set-mark command as M-x set-mark-command (but who really wants to type all that every time?)

You could just get a different telnet program. There are a number of good freeware telnet clients available. See the “Downloads” section on the CS 252 Library page for some recommendations.

You can bind a different key to set-mark-command that you can type from within Windows telnet. Add the line:

(global-set-key "\M-\\" 'set-mark-command)

to your .emacs file, restart emacs, and you can set the mark with the key sequence M-\ (escape followed by a backslash)

I've added that global-set-key to my own .emacs file, so if you've copied that into your home directory as described earlier, that key binding will already be defined.

So to set up a region to operate on, you move the cursor to one end of the region, give the set-mark-command, then move the cursor to the other end of the region. Everything between the mark and the cursor constitutes the current region, and can be operated on by any region-based command. Some region commands of note are:

C-w: Kill the region, i.e., delete it but save the deleted text in the clipboard. You can “yank” (paste) the deleted text at the cursor position with C-y.
M-w: Copy the region, i.e., Save a copy of the region's text in the clipboard. You can “yank” (paste) the deleted text at the cursor position with C-y.
C-xC-x: Exchanges the mark and the cursor. Hitting this repeatedly will flip you back and forth between the start and end of the current region. Although often useful in its own right, this command also provides a quick way to check and see if the region is really where you think it is.
C-cC-c: Comment out a region - in C++ and other programming modes, places comment markers in front of each line in the region.
M-x spell-region: Run a spell check on all text in the region.