Command and Input Mode

The hardest thing to understand about vi is the concept of modes. When using vi, you're always in either Command or Input mode. Unfortunately there's no clue as to which mode is currently active. In Command mode, you can move the cursor, search for characters, and delete existing text. But to enter or edit new text, you have to switch to Input mode.

When you start vi, you're in Command mode. To enter Input mode, type the letter a (lowercase only) to signal that you want to add text after the cursor position. Press esc to switch back to Command mode at any time.

Here's how to create a file from scratch using vi. To start, create a new file named cow.joke by typing

vi cow.joke

You'll see a screen that looks like this:

Adding New Text to Your File

Your cursor (the vertical bar at the top of the figure below is in the upper-left corner of the screen, and the message at the bottom tells you that a new file called cow.joke was just created. The tilde characters in the first column are just placeholders for empty lines.

Now press the letter a to enter Input mode and type the lines shown in here. Press enter at the end of each line to go on to the next.

Saving Your Work

So far, so good--let's save this little masterpiece. You're still in Input mode, so press esc to enter Command mode; then type ZZ (to put your file to sleep). You won't see any Z's on the screen, but after you've entered the second Z, your file will disappear, your Linux command prompt will return, and you'll see this message, indicating that your file was successfully saved:

"cow.joke" 6 lines, 113 characters.

Congratulations--you've just survived your first encounter with vi. You know that the a command switches to Input mode, esc gets you back to Command mode, and ZZ saves the file, but you'll have to expand this limited repertoire to get any real work done.

Common vi Commands

Have a look at this list of common vi commands (there are many more, but these will at least allow you to get some basic work done). Then we'll do one more exercise before moving on.

Note: As with all of Linux, vi commands are case sensitive.

Positioning the Cursor

Entering Input Mode

Entering Command Mode

Exiting or Saving Your File

Trying Out Some vi Commands

Here's another example to try out some of the vi commands. Enter the following command to fire up vi again, and you should see the file as we left it in the last example:

vi cow.joke

Changing Text

Let's change Bill's name to Biff on the second line. To do so, use the arrow keys to position your cursor on the third character of line 2 (the letter "l" in Bill); then press x twice (to delete the two l's). Now press i (to enter Input mode) and then type ff to complete the change from Bill to Biff.

Tip: Be careful about pressing the arrow keys while you're in Input mode. In some versions of vi you can position the cursor only in Command mode. Yuck.

You could also have used the R command to do this job of replacing text, so use it to change the other Bill now. Press esc to enter Command mode; then type /Bill to search for the word Bill. The cursor should move to line 4, right to where Bill is located.

Now position your cursor on the third character (the letter "l"), press R to replace the characters, and type ff. Both Bills should now be Biffs.

Adding and Deleting Lines

Here's how to add or delete a line. Press esc to enter Command mode; then press the o key to add a new line. You're in Input mode again, so you can type whatever you like on this new line. But that would ruin the joke, so delete this new line by pressing esc and then entering the dd command. The line you just added should go away.

Quitting without Saving Your Changes

Hmmm. . . . "Biff" just doesn't have that wholesome ring to it, so let's forget about all the changes we've made in this editing session and exit vi without saving the file. Make sure you're in Command mode, enter the :q! command, and then press enter. Your Linux prompt should return, and the cow.joke file will be just as it was before.

Parting Words about vi

Using vi can be frustrating, but it really isn't rocket science once you get used to the concept of the two modes and get the hang of when it's okay to move your cursor or enter text. If you're ever unsure about which mode you're in, simply press esc once or twice, and you can be sure you're in Command mode.

There are some powerful (but arcane) commands that diehard vi users use to get things done quickly in this relic-of-the-sixties text editor. The man vi command will tell you a lot more about vi if you decide you want to become proficient.

The Usenet newsgroup comp.editors is a good place to discuss vi or ask questions. You can find the vi FAQ (Frequently Asked Questions) file on the Web at http://www.faqs.org/faqs/editor-faq/vi/.

For more information on the vi command, see the vi manual.

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