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- [Ch 24 - Vimscript Basic Data Types](./ch24_vimscript_basic_data_types)
- [Ch 25 - Vimscript Basic Expressions](./ch25_vimscript_equalities_conditionals_and_loops.md)
- Ch 26 - Vimscript Variable Scopes
- [Ch 26 - Vimscript Variable Scopes](./ch26_vimscript_variables_scopes.md)
- Ch 27 - Vimscript Functions
# Translations

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---
title: "Variables and Scopes"
metaTitle: "Variables and Scopes"
metaDescription: "What are the different variable scopes in Vim?"
---
Before diving into Vimscript functions, let's learn about the different sources and scopes of Vim variables.
## `let` and `const`
You can assign a value to a variable in Vim with `let`:
```
let pancake = "pancake"
```
Later you can call that variable any time.
```
echo pancake
" returns "pancake"
```
`let` is mutable, meaning you can change the value at any time in the future.
```
let pancake = "not waffles"
echo pancake
" returns "not waffles"
```
Notice that when you want to change the value of a set variable, you still need to use `let`.
```
let beverage = "milk"
beverage = "orange juice"
" throws an error
```
You can define an immutable variable with `const` (both Vim variable setters are similar to Javascript's `let` and `const`).
```
const waffle = "waffle"
echo waffle
"return waffle
const waffle = "pancake"
" returns error
let waffle = "pancake"
" returns error
```
Before learning native Vimscript variables, it's good to learn the different sources of Vim variables that you can use. There are three more "variables" you can use inside Vim expressions: environment variable, option variable, and register variable.
### Environment Variable (`$VAR`)
Suppose that you have a `SHELL` environment variable already available in your terminal. To access it from Vim:
```
echo $SHELL
" returns $SHELL value. In my case, it returns /bin/bash
```
### Option variable
You can access Vim options with `&` (options are the settings you access with `:set`). To see what background Vim uses, you can run:
```
echo &background
" returns either "light" or "dark"
```
Alternatively, you can always run `set background?` to see the value of the `background` option.
### Register variable
You can access Vim registers (Ch. 08) with `@`. Suppose the value "chocolate" is already saved to register `a`. To access it, you can use `@a`. You can also update it with `let`.
```
echo @a
" returns chocolate
let @a .= " donut"
echo @a
" returns "chocolate donut"
```
Now when you paste from register `a` (`"ap`), it will return "chocolate donut".
The operator `.=` concatenates two strings. The expression `let @a .= " donut"` is the same as `let @a = @a . " donut"`
## Variable Scopes
There are 9 variable scopes in Vim. You can recognize them from their prepended letter:
```
g: Global variable
{nothing} Global variable
b: Buffer-local variable
w: Window-local variable
t: Tab-local variable
s: Sourced Vimscript variable
l: Function-local variable
a: Function formal parameter variable
v: Built-in Vim variable
```
### Global variable
When you are declaring a "regular" variable:
```
let pancake = "pancake"
```
`pancake` is actually a global variable. When you define a global variable, you can call them from anywhere.
Prepending `g:` to a variable also creates a global variable.
```
let g:waffle = "waffle"
```
Both `pancake` and `g:waffle` have the same scope. You can call each of them with either syntax.
```
echo pancake
" returns "pancake"
echo g:pancake
"returns "pancake"
echo waffle
" returns "waffle"
echo g:waffle
" returns "waffle"
```
### Buffer variable
A variable preceded with `b:` is a buffer variable. A buffer variable is a variable that is local to the current buffer (Ch 02). If you have multiple buffers open, each buffer will have their own separate list of buffer variables.
In buffer 1:
```
const b:donut = "chocolate donut"
```
In buffer 2:
```
const b:donut = "blueberry donut"
```
Each `b:donut` buffer variable lives inside buffers 1 and 2, respectively.
On the side note, Vim has a *special* buffer variable `b:changedtick` that keeps track of all the changes done to the current buffer.
1. Run `echo b:changedtick` and note the number it returns..
2. Make changes in Vim.
3. Run `echo b:changedtick` again and note the number it now returns.
### Window variable
A variable preceded with `w:` is a window variable. It exists only in that window.
In window 1:
```
const w:donut = "chocolate donut"
```
In window 2:
```
const w:donut = "raspberry donut"
```
On each window, you can call `echo w:donut` to get unique values.
### Tab variable
A variable preceded with `t:` is a tab variable. It exists only in that tab.
In tab 1:
```
const t:donut = "chocolate donut"
```
In tab 2:
```
const t:donut = "blackberry donut"
```
On each tab, you can call `echo t:donut` to get unique values.
### Script variable
A variable preceded with `s:` is a script variable. These variables can only be accessed from inside scripts.
If you have an arbitrary file `script.vim` and inside it you have:
```
let s:dozen = 12
function Consume()
let s:dozen -= 1
echo s:dozen " is left"
endfunction
```
Source the file with `:source dozen.vim`. Now call the `Consume` function:
```
:call Consume()
" returns "11 is left"
:call Consume()
" returns "10 is left"
:echo s:dozen
" Undefined variable error
```
The `Consume` function can be called directly and it increments as expected. When you try to read `s:dozen` directly, Vim won't find it because you are out of scope. `s:dozen` script variable is only accessible from inside `script.vim`.
Each time you source the `script.vim` file, it resets the `s:dozen` counter. If you are in the middle of decrementing `s:dozen` value and you run `:source dozen.vim`, the counter resets back to 12. This can be a problem for unsuspecting users. To fix this issue, refactor the code:
```
if !exists("s:dozen")
let s:dozen = 12
endif
function Consume()
let s:dozen -= 1
echo s:dozen
endfunction
```
### Function-local and Function formal parameter variable
Both the function-local variable (`l:`) and the function formal variable (`a:`) will be covered in the next chapter.
### Built-in Vim variables
A variable prepended with `v:` is a special built-in Vim variable. You cannot define these variables. You have seen some of them already. For example:
- `v:version` tells you what Vim version you are using.
- `v:key` contains the current item value when iterating through a dictionary.
- `v:val` contains the current item value when running a `map()` or `filter()` operation.
- `v:true`, `v:false`, `v:null`, and `v:none` are special data types.
There are other variables. For a list of Vim built-in variables, check out `:h vim-variable` or `:h v:`.
## Using Vim Variables The Smart Way
Being able to quickly access environment, option, and register variables give you a broad flexibility to customize your editor and terminal environment. You also learned that Vim has 9 different Vimscript variable scopes, each existing under a certain constraints. You can take advantage of these unique variable types to write your own custom plugins. But before that, let's learn how to create functions!