chapters/03.markdown @ 8d88c7586ef3 jlmuir/fix-typo-in-ch-20-start-starts-1475252546552

Basic Mapping
=============

If there's one feature of Vimscript that will let you bend Vim to your will more
than any other, it's the ability to map keys.  Mapping keys lets you tell Vim:

> When I press this key, I want you to do this stuff instead of whatever you
> would normally do.

We're going to start off by mapping keys in normal mode.  We'll talk about how
to map keys in insert and other modes in the next chapter.

Type a few lines of text into a file, then run:

    :::vim
    :map - x

Put your cursor somewhere in the text and press `-`.  Notice how Vim deleted the
character under the cursor, just like if you had pressed `x`.

We already have a key for "delete the character under the cursor", so let's
change that mapping to something slightly more useful.  Run this command:

    :::vim
    :map - dd

Now put your cursor on a line somewhere and press `-` again.  This time Vim
deletes the entire line, because that's what `dd` does.

Special Characters
------------------

You can use `<keyname>` to tell Vim about special keys.  Try running this
command:

    :::vim
    :map <space> viw

Put your cursor on a word in your text and press the space bar.  Vim will
visually select the word.

You can also map modifier keys like Ctrl and Alt.  Run this:

    :::vim
    :map <c-d> dd

Now pressing `Ctrl+d` on your keyboard will run `dd`.

Commenting
----------

Remember in the first lesson where we talked about comments?  Mapping keys is
one of the places where Vim comments don't work.  Try running this command:

    :::vim
    :map <space> viw " Select word

If you try pressing space now, something horrible will almost certainly happen.
Why?

When you press the space bar now, Vim thinks you want it to do what
`viw<space>"<space>Select<space>word` would do.  Obviously this isn't what we
want.

If you look closely at the effect of this mapping you might notice something
strange.  Take a few minutes to try to figure out exactly what happens when you
use it, and *why* that happens.

Don't worry if you don't get it right away -- we'll talk about it more soon.

Exercises
---------

Map the `-` key to "delete the current line, then paste it below the one we're
on now".  This will let you move lines downward in your file with one keystroke.

Add that mapping command to your `~/.vimrc` file so you can use it any time
you start Vim.

Figure out how to map the `_` key to move the line up instead of down.

Add that mapping to your `~/.vimrc` file too.

Try to guess how you might remove a mapping and reset a key to its normal
function.