Lua-guide

Nvim :help pages, generated from source using the tree-sitter-vimdoc parser.


Guide to using Lua in Nvim

Introduction

This guide will go through the basics of using Lua in Neovim. It is not meant to be a comprehensive encyclopedia of all available features, nor will it detail all intricacies. Think of it as a survival kit -- the bare minimum needed to know to comfortably get started on using Lua in Neovim.
An important thing to note is that this isn't a guide to the Lua language itself. Rather, this is a guide on how to configure and modify Neovim through the Lua language and the functions we provide to help with this. Take a look at luaref and lua-concepts if you'd like to learn more about Lua itself. Similarly, this guide assumes some familiarity with the basics of Neovim (commands, options, mappings, autocommands), which are covered in the user-manual.

Some words on the API lua-guide-api

The purpose of this guide is to introduce the different ways of interacting with Neovim through Lua (the "API"). This API consists of three different layers:
1. The "Vim API" inherited from Vim: ex-commands and builtin-functions as well as user-functions in Vimscript. These are accessed through vim.cmd() and vim.fn respectively, which are discussed under lua-guide-vimscript below.
2. The "Neovim API" written in C for use in remote plugins and GUIs; see api. These functions are accessed through vim.api.
3. The "Lua API" written in and specifically for Lua. These are any other functions accessible through vim.* not mentioned already; see lua-stdlib.
This distinction is important, as API functions inherit behavior from their original layer: For example, Neovim API functions always need all arguments to be specified even if Lua itself allows omitting arguments (which are then passed as nil); and Vim API functions can use 0-based indexing even if Lua arrays are 1-indexed by default.
Through this, any possible interaction can be done through Lua without writing a complete new API from scratch. For this reason, functions are usually not duplicated between layers unless there is a significant benefit in functionality or performance (e.g., you can map Lua functions directly through nvim_create_autocmd() but not through :autocmd). In case there are multiple ways of achieving the same thing, this guide will only cover what is most convenient to use from Lua.

Using Lua lua-guide-using-Lua

To run Lua code from the Neovim command line, use the :lua command:
:lua print("Hello!")
Note: each :lua command has its own scope and variables declared with the local keyword are not accessible outside of the command. This won't work:
:lua local foo = 1
:lua print(foo)
" prints "nil" instead of "1"
You can also use :lua=, which is the same as :lua vim.pretty_print(...), to conveniently check the value of a variable or a table:
:lua=package
To run a Lua script in an external file, you can use the :source command exactly like for a Vimscript file:
:source ~/programs/baz/myluafile.lua
Finally, you can include Lua code in a Vimscript file by putting it inside a lua-heredoc block:
lua << EOF
  local tbl = {1, 2, 3}
  for k, v in ipairs(tbl) do
    print(v)
  end
EOF

Using Lua files on startup lua-guide-config

Neovim supports using init.vim or init.lua as the configuration file, but not both at the same time. This should be placed in your config directory, which is typically ~/.config/nvim for Linux, BSD, or macOS, and ~/AppData/Local/nvim/ for Windows. Note that you can use Lua in init.vim and Vimscript in init.lua, which will be covered below.
If you'd like to run any other Lua script on startup automatically, then you can simply put it in plugin/ in your 'runtimepath'.

Lua modules lua-guide-modules

If you want to load Lua files on demand, you can place them in the lua/ directory in your 'runtimepath' and load them with require. (This is the Lua equivalent of Vimscript's autoload mechanism.)
Let's assume you have the following directory structure:
~/.config/nvim
|-- after/
|-- ftplugin/
|-- lua/
|  |-- myluamodule.lua
|  |-- other_modules/
|     |-- anothermodule.lua
|     |-- init.lua
|-- plugin/
|-- syntax/
|-- init.vim
Then the following Lua code will load myluamodule.lua:
require("myluamodule")
Note the absence of a .lua extension.
Similarly, loading other_modules/anothermodule.lua is done via
require('other_modules/anothermodule')
-- or
require('other_modules.anothermodule')
Note how "submodules" are just subdirectories; the . is equivalent to the path separator / (even on Windows).
A folder containing an init.lua file can be required directly, without having to specify the name of the file:
require('other_modules') -- loads other_modules/init.lua
Requiring a nonexistent module or a module which contains syntax errors aborts the currently executing script. pcall() may be used to catch such errors. The following example tries to load the module_with_error and only calls one of its functions if this succeeds and prints an error message otherwise:
local ok, mymod = pcall(require, 'module_with_error')
if not ok then
  print("Module had an error")
else
  mymod.function()
end
In contrast to :source, require() not only searches through all lua/ directories under 'runtimepath', it also cache the module on first use. Calling require() a second time will therefore _not_ execute the script again and instead return the cached file. To rerun the file, you need to remove it from the cache manually first:
package.loaded['myluamodule'] = nil
require('myluamodule')    -- read and execute the module again from disk

Using Vim commands and functions from Lua lua-guide-vimscript

All Vim commands and functions are accessible from Lua.

Vim commands lua-guide-vim-commands

To run an arbitrary Vim command from Lua, pass it as a string to vim.cmd():
vim.cmd("colorscheme habamax")
Note that special characters will need to be escaped with backslashes:
vim.cmd("%s/\\Vfoo/bar/g")
An alternative is to use a literal string (see luaref-literal) delimited by double brackets [[ ]] as in
vim.cmd([[%s/\Vfoo/bar/g]])
Another benefit of using literal strings is that they can be multiple lines; this allows you to pass multiple commands to a single call of vim.cmd():
vim.cmd([[
  highlight Error guibg=red
  highlight link Warning Error
]])
This is the converse oflua-heredoc and allows you to include Vimscript code in your init.lua.
If you want to build your Vim command programmatically, the following form can be useful (all these are equivalent to the corresponding line above):
vim.cmd.colorscheme("habamax")
vim.cmd.highlight({ "Error", "guibg=red" })
vim.cmd.highlight({ "link", "Warning", "Error" })

Vimscript functions lua-guide-vim-functions

Use vim.fn to call Vimscript functions from Lua. Data types between Lua and Vimscript are automatically converted:
print(vim.fn.printf('Hello from %s', 'Lua'))
local reversed_list = vim.fn.reverse({ 'a', 'b', 'c' })
print(vim.inspect(reversed_list)) -- { "c", "b", "a" }
local function print_stdout(chan_id, data, name)
  print(data[1])
end
vim.fn.jobstart('ls', { on_stdout = print_stdout })
print(vim.fn.printf('Hello from %s', 'Lua'))
This works for both builtin-functions and user-functions.
Note that hashes (#) are not valid characters for identifiers in Lua, so, e.g., autoload functions have to be called with this syntax:
vim.fn['my#autoload#function']()

See also:

builtin-functions: alphabetic list of all Vimscript functions
function-list: list of all Vimscript functions grouped by topic
:runtime: run all Lua scripts matching a pattern in 'runtimepath'
package.path: list of all paths searched by require()

Variables lua-guide-variables

Variables can be set and read using the following wrappers, which directly correspond to their variable-scope:
vim.g: global variables (g:)
vim.b: variables for the current buffer (b:)
vim.w: variables for the current window (w:)
vim.t: variables for the current tabpage (t:)
vim.v: predefined Vim variables (v:)
vim.env: environment variables defined in the editor session
Data types are converted automatically. For example:
vim.g.some_global_variable = {
  key1 = "value",
  key2 = 300
}
print(vim.inspect(vim.g.some_global_variable))
--> { key1 = "value", key2 = 300 }
You can target specific buffers (via number), windows (via window-ID), or tabpages by indexing the wrappers:
vim.b[2].myvar = 1               -- set myvar for buffer number 2
vim.w[1005].myothervar = true    -- set myothervar for window ID 1005
Some variable names may contain characters that cannot be used for identifiers in Lua. You can still manipulate these variables by using the syntax
vim.g['my#variable'] = 1
Note that you cannot directly change fields of array variables. This won't work:
vim.g.some_global_variable.key2 = 400
vim.pretty_print(vim.g.some_global_variable)
--> { key1 = "value", key2 = 300 }
Instead, you need to create an intermediate Lua table and change this:
local temp_table = vim.g.some_global_variable
temp_table.key2 = 400
vim.g.some_global_variable = temp_table
vim.pretty_print(vim.g.some_global_variable)
--> { key1 = "value", key2 = 400 }
To delete a variable, simply set it to nil:
vim.g.myvar = nil

Options lua-guide-options

There are two complementary ways of setting options via Lua.

vim.opt

The most convenient way for setting global and local options, e.g., in init.lua, is through vim.opt and friends:
vim.opt: behaves like :set
vim.opt_global: behaves like :setglobal
vim.opt_local: behaves like :setlocal
For example, the Vimscript commands
set smarttab
set nosmarttab
are equivalent to
vim.opt.smarttab = true
vim.opt.smarttab = false
In particular, they allow an easy way to working with list-like, map-like, and set-like options through Lua tables: Instead of
set wildignore=*.o,*.a,__pycache__
set listchars=space:_,tab:>~
set formatoptions=njt
you can use
vim.opt.wildignore = { '*.o', '*.a', '__pycache__' }
vim.opt.listchars = { space = '_', tab = '>~' }
vim.opt.formatoptions = { n = true, j = true, t = true }
These wrappers also come with methods that work similarly to their :set+=, :set^= and :set-= counterparts in Vimscript:
vim.opt.shortmess:append({ I = true })
vim.opt.wildignore:prepend('*.o')
vim.opt.whichwrap:remove({ 'b', 's' })
The price to pay is that you cannot access the option values directly but must use vim.opt:get():
print(vim.opt.smarttab)
--> {...} (big table)
print(vim.opt.smarttab:get())
--> false
vim.pretty_print(vim.opt.listchars:get())
--> { space = '_', tab = '>~' }

vim.o

For this reason, there exists a more direct variable-like access using vim.o and friends, similarly to how you can get and set options via :echo &number and :let &listchars='space:_,tab:>~':
vim.o: behaves like :set
vim.go: behaves like :setglobal
vim.bo: for buffer-scoped options
vim.wo: for window-scoped options
For example:
vim.o.smarttab = false -- :set nosmarttab
print(vim.o.smarttab)
--> false
vim.o.listchars = 'space:_,tab:>~' -- :set listchars='space:_,tab:>~'
print(vim.o.listchars)
--> 'space:_,tab:>~'
vim.o.isfname = vim.o.isfname .. ',@[email protected]' -- :set [email protected]@
print(vim.o.isfname)
--> '@,48-57,/,.,-,_,+,,,#,$,%,~,=,@[email protected]'
vim.bo.shiftwidth = 4 -- :setlocal shiftwidth=4
print(vim.bo.shiftwidth)
--> 4
Just like variables, you can specify a buffer number or window-ID for buffer and window options, respectively. If no number is given, the current buffer or window is used:
vim.bo[4].expandtab = true -- sets expandtab to true in buffer 4
vim.wo.number = true       -- sets number to true in current window
print(vim.wo[0].number)    --> true

See also:

Mappings lua-guide-mappings

You can map either Vim commands or Lua functions to key sequences.

Creating mappings lua-guide-mappings-set

Mappings can be created using vim.keymap.set(). This function takes three mandatory arguments:
{mode} is a string or a table of strings containing the mode prefix for which the mapping will take effect. The prefixes are the ones listed in :map-modes, or "!" for :map!, or empty string for :map.
{lhs} is a string with the key sequences that should trigger the mapping.
{rhs} is either a string with a Vim command or a Lua function that should be executed when the {lhs} is entered. An empty string is equivalent to <Nop>, which disables a key.
Examples:
-- Normal mode mapping for Vim command
vim.keymap.set('n', '<Leader>ex1', '<cmd>echo "Example 1"<cr>')
-- Normal and Command-line mode mapping for Vim command
vim.keymap.set({'n', 'c'}, '<Leader>ex2', '<cmd>echo "Example 2"<cr>')
-- Normal mode mapping for Lua function
vim.keymap.set('n', '<Leader>ex3', vim.treesitter.start)
-- Normal mode mapping for Lua function with arguments
vim.keymap.set('n', '<Leader>ex4', function() print('Example 4') end)
You can map functions from Lua modules via
vim.keymap.set('n', '<Leader>pl1', require('plugin').action)
Note that this loads the plugin at the time the mapping is defined. If you want to defer the loading to the time when the mapping is executed (as for autoload functions), wrap it in function() end:
vim.keymap.set('n', '<Leader>pl2', function() require('plugin').action() end)
The fourth, optional, argument is a table with keys that modify the behavior of the mapping such as those from :map-arguments. The following are the most useful options:
buffer: If given, only set the mapping for the buffer with the specified number; 0 or true means the current buffer.
-- set mapping for the current buffer
vim.keymap.set('n', '<Leader>pl1', require('plugin').action, { buffer = true })
-- set mapping for the buffer number 4
vim.keymap.set('n', '<Leader>pl1', require('plugin').action, { buffer = 4 })
silent: If set to true, suppress output such as error messages.
vim.keymap.set('n', '<Leader>pl1', require('plugin').action, { silent = true })
expr: If set to true, do not execute the {rhs} but use the return value as input. Special keycodes are converted automatically. For example, the following mapping replaces <down> with <c-n> in the popupmenu only:
vim.keymap.set('c', '<down>', function()
  if vim.fn.pumvisible() == 1 then return '<c-n>' end
  return '<down>'
end, { expr = true })
desc: A string that is shown when listing mappings with, e.g., :map. This is useful since Lua functions as {rhs} are otherwise only listed as Lua: <number> <source file>:<line>. Plugins should therefore always use this for mappings they create.
vim.keymap.set('n', '<Leader>pl1', require('plugin').action,
  { desc = 'Execute action from plugin' })
remap: By default, all mappings are nonrecursive by default (i.e., vim.keymap.set() behaves like :noremap). If the {rhs} is itself a mapping that should be executed, set remap = true:
vim.keymap.set('n', '<Leader>ex1', '<cmd>echo "Example 1"<cr>')
-- add a shorter mapping
vim.keymap.set('n', 'e', '<Leader>ex1', { remap = true })
Note: <Plug> mappings are always expanded even with the default remap = false:
vim.keymap.set('n', '[%', '<Plug>(MatchitNormalMultiBackward)')

Removing mappings lua-guide-mappings-del

A specific mapping can be removed with vim.keymap.del():
vim.keymap.del('n', '<Leader>ex1')
vim.keymap.del({'n', 'c'}, '<Leader>ex2', {buffer = true})

See also:

vim.api.nvim_get_keymap(): return all global mapping
vim.api.nvim_buf_get_keymap(): return all mappings for buffer

Autocommands lua-guide-autocommands

An autocommand is a Vim command or a Lua function that is automatically executed whenever one or more events are triggered, e.g., when a file is read or written, or when a window is created. These are accessible from Lua through the Neovim API.

Creating autocommands lua-guide-autocommand-create

Autocommands are created using vim.api.nvim_create_autocmd(), which takes two mandatory arguments:
{event}: a string or table of strings containing the event(s) which should trigger the command or function.
{opts}: a table with keys that control what should happen when the event(s) are triggered.
The most important options are:
pattern: A string or table of strings containing the autocmd-pattern. Note: Environment variable like $HOME and ~ are not automatically expanded; you need to explicitly use vim.fn.expand() for this.
command: A string containing a Vim command.
callback: A Lua function.
You must specify one and only one of command and callback. If pattern is omitted, it defaults to pattern = '*'. Examples:
vim.api.nvim_create_autocmd({"BufEnter", "BufWinEnter"}, {
  pattern = {"*.c", "*.h"},
  command = "echo 'Entering a C or C++ file'",
})
-- Same autocommand written with a Lua function instead
vim.api.nvim_create_autocmd({"BufEnter", "BufWinEnter"}, {
  pattern = {"*.c", "*.h"},
  callback = function() print("Entering a C or C++ file") end,
})
-- User event triggered by MyPlugin
vim.api.nvim_create_autocmd("User", {
  pattern = "MyPlugin",
  callback = function() print("My Plugin Works!") end,
})
Neovim will always call a Lua function with a single table containing information about the triggered autocommand. The most useful keys are
match: a string that matched the pattern (see <amatch>)
buf: the number of the buffer the event was triggered in (see <abuf>)
file: the file name of the buffer the event was triggered in (see <afile>)
data: a table with other relevant data that is passed for some events
For example, this allows you to set buffer-local mappings for some filetypes:
vim.api.nvim.create_autocmd("FileType", {
  pattern = "lua",
  callback = function(args)
    vim.keymap.set('n', 'K', vim.lsp.buf.hover, { buffer = args.buf })
  end
})
This means that if your callback itself takes an (even optional) argument, you must wrap it in function() end to avoid an error:
vim.api.nvim_create_autocmd('TextYankPost', {
  callback = function() vim.highlight.on_yank() end
})
(Since unused arguments can be omitted in Lua function definitions, this is equivalent to function(args) ... end.)
Instead of using a pattern, you can create a buffer-local autocommand (see autocmd-buflocal) with buffer; in this case, pattern cannot be used:
-- set autocommand for current buffer
vim.api.nvim_create_autocmd("CursorHold", {
  buffer = 0,
  callback = function() print("hold") end,
})
-- set autocommand for buffer number 33
vim.api.nvim_create_autocmd("CursorHold", {
  buffer = 33,
  callback = function() print("hold") end,
})
Similarly to mappings, you can (and should) add a description using desc:
vim.api.nvim_create_autocmd('TextYankPost', {
  callback = function() vim.highlight.on_yank() end,
  desc = "Briefly highlight yanked text"
})
Finally, you can group autocommands using the group key; this will be covered in detail in the next section.

Grouping autocommands lua-guide-autocommands-group

Autocommand groups can be used to group related autocommands together; see autocmd-groups. This is useful for organizing autocommands and especially for preventing autocommands to be set multiple times.
Groups can be created with vim.api.nvim_create_augroup(). This function takes two mandatory arguments: a string with the name of a group and a table determining whether the group should be cleared (i.e., all grouped autocommands removed) if it already exists. The function returns a number that is the internal identifier of the group. Groups can be specified either by this identifier or by the name (but only if the group has been created first).
For example, a common Vimscript pattern for autocommands defined in files that may be reloaded is
augroup vimrc
  " Remove all vimrc autocommands
  autocmd!
  au BufNewFile,BufRead *.html set shiftwidth=4
  au BufNewFile,BufRead *.html set expandtab
augroup END
This is equivalent to the following Lua code:
local mygroup = vim.api.nvim_create_augroup('vimrc', { clear = true })
vim.api.nvim_create_autocmd({ 'BufNewFile', 'BufRead' }, {
  pattern = '*.html',
  group = mygroup,
  command = 'set shiftwidth=4',
})
vim.api.nvim_create_autocmd({ 'BufNewFile', 'BufRead' }, {
  pattern = '*.html',
  group = 'vimrc',  -- equivalent to group=mygroup
  command = 'set expandtab',
})
Autocommand groups are unique for a given name, so you can reuse them, e.g., in a different file:
local mygroup = vim.api.nvim_create_augroup('vimrc', { clear = false })
vim.api.nvim_create_autocmd({ 'BufNewFile', 'BufRead' }, {
  pattern = '*.html',
  group = mygroup,
  command = 'set shiftwidth=4',
})

Deleting autocommands lua-guide-autocommands-delete

You can use vim.api.nvim_clear_autocmds() to remove autocommands. This function takes a single mandatory argument that is a table of keys describing the autocommands that are to be removed:
-- Delete all BufEnter and InsertLeave autocommands
vim.api.nvim_clear_autocmds({event = {"BufEnter", "InsertLeave"}})
-- Delete all autocommands that uses "*.py" pattern
vim.api.nvim_clear_autocmds({pattern = "*.py"})
-- Delete all autocommands in group "scala"
vim.api.nvim_clear_autocmds({group = "scala"})
-- Delete all ColorScheme autocommands in current buffer
vim.api.nvim_clear_autocmds({event = "ColorScheme", buffer = 0 })
Note: Autocommands in groups will only be removed if the group key is specified, even if another option matches it.

See also

nvim_get_autocmds(): return all matching autocommands
nvim_exec_autocmds(): execute all matching autocommands

User commands lua-guide-usercommands

user-commands are custom Vim commands that call a Vimscript or Lua function. Just like built-in commands, they can have arguments, act on ranges, or have custom completion of arguments. As these are most useful for plugins, we will cover only the basics of this advanced topic.

Creating user commands lua-guide-usercommands-create

User commands can be created through the Neovim API with vim.api.nvim_create_user_command(). This function takes three mandatory arguments:
a string that is the name of the command (which must start with an uppercase letter to distinguish it from builtin commands);
a string containing Vim commands or a Lua function that is executed when the command is invoked;
a table with command-attributes; in addition, it can contain the keys desc (a string describing the command); force (set to false to avoid replacing an already existing command with the same name), and preview (a Lua function that is used for :command-preview).
Example:
vim.api.nvim_create_user_command('Test', 'echo "It works!"', {})
vim.cmd.Test()
--> It works!
(Note that the third argument is mandatory even if no attributes are given.)
Lua functions are called with a single table argument containing arguments and modifiers. The most important are:
name: a string with the command name
fargs: a table containing the command arguments split by whitespace (see <f-args>)
bang: true if the command was executed with a ! modifier (see <bang>)
line1: the starting line number of the command range (see <line1>)
line2: the final line number of the command range (see <line2>)
range: the number of items in the command range: 0, 1, or 2 (see <range>)
count: any count supplied (see <count>)
smods: a table containing the command modifiers (see <mods>)
For example:
vim.api.nvim_create_user_command('Upper',
  function(opts)
    print(string.upper(opts.fargs[1]))
  end,
  { nargs = 1 })
vim.cmd.Upper('foo')
--> FOO
The complete attribute can take a Lua function in addition to the attributes listed in :command-complete.
vim.api.nvim_create_user_command('Upper',
  function(opts)
    print(string.upper(opts.fargs[1]))
  end,
  { nargs = 1,
    complete = function(ArgLead, CmdLine, CursorPos)
      -- return completion candidates as a list-like table
      return { "foo", "bar", "baz" }
    end,
})
Buffer-local user commands are created with vim.api.nvim_buf_create_user_command(). Here the first argument is the buffer number (0 being the current buffer); the remaining arguments are the same as for nvim_create_user_command():
vim.api.nvim_buf_create_user_command(0, 'Upper',
  function(opts)
    print(string.upper(opts.fargs[1]))
  end,
  { nargs = 1 })

Deleting user commands lua-guide-usercommands-delete

User commands can be deleted with vim.api.nvim_del_user_command(). The only argument is the name of the command:
vim.api.nvim_del_user_command('Upper')
To delete buffer-local user commands use vim.api.nvim_buf_del_user_command(). Here the first argument is the buffer number (0 being the current buffer), and second is command name:
vim.api.nvim_buf_del_user_command(4, 'Upper')

Credits lua-guide-credits

This guide is in large part taken from nanotee's Lua guide: https://github.com/nanotee/nvim-lua-guide
Thank you @nanotee!
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