Avoid destroying record of last visual selection
author |
Daniel Robert Allen <allen.daniel.r@gmail.com> |
date |
Sun, 07 Apr 2013 11:33:46 -0700 |
parents |
f09f87e10570 |
children |
(none) |
Variables
=========
Up to this point we've covered single commands. For the next third of the book
we're going to look at Vimscript as a *programming language*. This won't be as
instantly gratifying as the rest of what you've learned, but it will lay the
groundwork for the last part of the book, which walks through creating
a full-fledged Vim plugin from scratch.
Let's get started. The first thing we need to talk about are variables. Run
the following commands:
:::vim
:let foo = "bar"
:echo foo
Vim will display `bar`. `foo` is now a variable, and we've assigned it
a string: `"bar"`. Now run these commands:
:::vim
:let foo = 42
:echo foo
Vim will display `42`, because we've reassigned `foo` to the integer `42`.
From these short examples it may seem like Vimscript is dynamically typed.
That's not the case, but we'll talk more about that later.
Options as Variables
--------------------
You can read and set *options* as variables by using a special syntax. Run the
following commands:
:::vim
:set textwidth=80
:echo &textwidth
Vim will display `80`. Using an ampersand in front of a name tells Vim that
you're referring to the option, not a variable that happens to have the same
name.
Let's see how Vim works with boolean options. Run the following commands:
:::vim
:set nowrap
:echo &wrap
Vim displays `0`. Now try these commands:
:::vim
:set wrap
:echo &wrap
This time Vim displays `1`. This is a very strong hint that Vim treats the
integer `0` as "false" and the integer `1` as "true". It would be reasonable to
assume that Vim treats *any* non-zero integer as "truthy", and this is indeed
the case.
We can also *set* options as variables using the `let` command. Run the
following commands:
:::vim
:let &textwidth = 100
:set textwidth?
Vim will display `textwidth=100`.
Why would we want to do this when we could just use `set`? Run the following
commands:
:::vim
:let &textwidth = &textwidth + 10
:set textwidth?
This time Vim displays `textwidth=110`. When you set an option using `set` you
can only set it to a single literal value. When you use `let` and set it as
a variable you can use the full power of Vimscript to determine the value.
Local Options
-------------
If you want to set the *local* value of an option as a variable, instead of the
*global* value, you need to prefix the variable name.
Open two files in separate splits. Run the following command:
:::vim
:let &l:number = 1
Now switch to the other file and run this command:
:::vim
:let &l:number = 0
Notice that the first window has line numbers and the second does not.
Registers as Variables
----------------------
You can also read and set *registers* as variables. Run the following command:
:::vim
:let @a = "hello!"
Now put your cursor somewhere in your text and type `"ap`. This command tells
Vim to "paste the contents of register `a` here". We just set the contents of
that register, so Vim pastes `hello!` into your text.
Registers can also be read. Run the following command:
:::vim
:echo @a
Vim will echo `hello!`.
Select a word in your file and yank it with `y`, then run this command:
:::vim
:echo @"
Vim will echo the word you just yanked. The `"` register is the "unnamed"
register, which is where text you yank without specifying a destination will go.
Perform a search in your file with `/someword`, then run the following command:
:::vim
:echo @/
Vim will echo the search pattern you just used. This lets you programmatically
read *and modify* the current search pattern, which can be very useful at times.
Exercises
---------
Go through your `~/.vimrc` file and change some of the `set` and `setlocal`
commands to their `let` forms. Remember that boolean options still need to be
set to something.
Try setting a boolean option like `wrap` to something other than zero or one.
What happens when you set it to a different number? What happens if you set it
to a string?
Go back through your `~/.vimrc` file and undo the changes. You should never use
`let` if `set` will suffice -- it's harder to read.
Read `:help registers` and look over the list of registers you can read and
write.