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if_lua.txt For Vim version 7.4. Last change: 2012 Jun 29

      VIM REFERENCE MANUAL    by Luis Carvalho

The Lua Interface to Vim lua Lua

  1. Commands |lua-commands|
  2. The vim module |lua-vim|
  3. List userdata |lua-list|
  4. Dict userdata |lua-dict|
  5. Funcref userdata |lua-funcref|
  6. Buffer userdata |lua-buffer|
  7. Window userdata |lua-window|
  8. The luaeval function |lua-luaeval|

{Vi does not have any of these commands}

The Lua interface is available only when Vim was compiled with the |+lua| feature.

  1. Commands lua-commands


    :[range]lua {chunk} Execute Lua chunk {chunk}. {not in Vi}


:lua print("Hello, Vim!")
:lua local curbuf = vim.buffer() curbuf[7] = "line #7"


:[range]lua << {endmarker} {script} {endmarker} Execute Lua script {script}. {not in Vi} Note: This command doesn’t work when the Lua feature wasn’t compiled in. To avoid errors, see |script-here|.

{endmarker} must NOT be preceded by any white space. If {endmarker} is omitted from after the “<<”, a dot ‘.’ must be used after {script}, like for the |:append| and |:insert| commands. This form of the |:lua| command is mainly useful for including Lua code in Vim scripts.


function! CurrentLineInfo()
lua << EOF
local linenr = vim.window().line
local curline = vim.buffer()[linenr]
print(string.format("Current line [%d] has %d chars",
    linenr, #curline))



:[range]luado {body} Execute Lua function “function (line, linenr) {body} end” for each line in the [range], with the function argument being set to the text of each line in turn, without a trailing , and the current line number. If the value returned by the function is a string it becomes the text of the line in the current turn. The default for [range] is the whole file: “1,$”. {not in Vi}


:luado return string.format("%s\t%d", line:reverse(), #line)
:lua require"lpeg"
:lua -- balanced parenthesis grammar:
:lua bp = lpeg.P{ "(" * ((1 - lpeg.S"()") + lpeg.V(1))^0 * ")" }
:luado if bp:match(line) then return "-->\t" .. line end



:[range]luafile {file} Execute Lua script in {file}. {not in Vi} The whole argument is used as a single file name.


:luafile script.lua
:luafile %


All these commands execute a Lua chunk from either the command line (:lua and :luado) or a file (:luafile) with the given line [range]. Similarly to the Lua interpreter, each chunk has its own scope and so only global variables are shared between command calls. All Lua default libraries are available. In addition, Lua “print” function has its output redirected to the Vim message area, with arguments separated by a white space instead of a tab.

Lua uses the “vim” module (see |lua-vim|) to issue commands to Vim and manage buffers (|lua-buffer|) and windows (|lua-window|). However, procedures that alter buffer content, open new buffers, and change cursor position are restricted when the command is executed in the |sandbox|.

  1. The vim module lua-vim

Lua interfaces Vim through the “vim” module. The first and last line of the input range are stored in “vim.firstline” and “vim.lastline” respectively. The module also includes routines for buffer, window, and current line queries, Vim evaluation and command execution, and others.

vim.list([arg])     Returns an empty list or, if "arg" is a Lua
            table with numeric keys 1, ..., n (a
            "sequence"), returns a list l such that l[i] =
            arg[i] for i = 1, ..., n (see |List|).
            Non-numeric keys are not used to initialize
            the list. See also |lua-eval| for conversion
            rules. Example: >
                :lua t = {math.pi, false, say = 'hi'}
                :echo luaeval('vim.list(t)')
                :" [3.141593, 0], 'say' is ignored

< vim.dict([arg]) Returns an empty dictionary or, if “arg” is a Lua table, returns a dict d such that d[k] = arg[k] for all string keys k in “arg” (see |Dictionary|). Number keys are converted to strings. Keys that are not strings are not used to initialize the dictionary. See also |lua-eval| for conversion rules. Example: > :lua t = {math.pi, false, say = ‘hi’} :echo luaeval(‘vim.dict(t)’) :“ {‘say’: ‘hi’}, numeric keys ignored < vim.funcref({name}) Returns a Funcref to function {name} (see |Funcref|). It is equivalent to Vim’s "function”.

vim.buffer([arg])   If "arg" is a number, returns buffer with
            number "arg" in the buffer list or, if "arg"
            is a string, returns buffer whose full or short
            name is "arg". In both cases, returns 'nil'
            (nil value, not string) if the buffer is not
            found. Otherwise, if "toboolean(arg)" is
            'true' returns the first buffer in the buffer
            list or else the current buffer.

vim.window([arg])   If "arg" is a number, returns window with
            number "arg" or 'nil' (nil value, not string)
            if not found. Otherwise, if "toboolean(arg)"
            is 'true' returns the first window or else the
            current window.

vim.type({arg})     Returns the type of {arg}. It is equivalent to
            Lua's "type" function, but returns "list",
            "dict", "funcref", "buffer", or "window" if
            {arg} is a list, dictionary, funcref, buffer,
            or window, respectively. Examples: >
                :lua l = vim.list()
                :lua print(type(l), vim.type(l))
                :" userdata list

< vim.command({cmd}) Executes the vim (ex-mode) command {cmd}. Examples: > :lua vim.command"set tw=60" :lua vim.command"normal ddp" < vim.eval({expr}) Evaluates expression {expr} (see |expression|), converts the result to Lua, and returns it. Vim strings and numbers are directly converted to Lua strings and numbers respectively. Vim lists and dictionaries are converted to Lua userdata (see |lua-list| and |lua-dict|). Examples: > :lua tw = vim.eval"&tw" :lua print(vim.eval"{‘a’: ‘one’}“.a) < vim.line() Returns the current line (without the trailing ), a Lua string.

vim.beep()      Beeps.

vim.open({fname})   Opens a new buffer for file {fname} and
            returns it. Note that the buffer is not set as

  1. List userdata lua-list

List userdata represent vim lists, and the interface tries to follow closely Vim’s syntax for lists. Since lists are objects, changes in list references in Lua are reflected in Vim and vice-versa. A list “l” has the following properties and methods:


o "#l" is the number of items in list "l", equivalent to "len(l)"
    in Vim.
o "l[k]" returns the k-th item in "l"; "l" is zero-indexed, as in Vim.
    To modify the k-th item, simply do "l[k] = newitem"; in
    particular, "l[k] = nil" removes the k-th item from "l".
o "l()" returns an iterator for "l".


o "l:add(item)" appends "item" to the end of "l".
o "l:insert(item[, pos])" inserts "item" at (optional)
    position "pos" in the list. The default value for "pos" is 0.


:let l = [1, 'item']
:lua l = vim.eval('l') -- same 'l'
:lua l:add(vim.list())
:lua l[0] = math.pi
:echo l[0] " 3.141593
:lua l[0] = nil -- remove first item
:lua l:insert(true, 1)
:lua print(l, #l, l[0], l[1], l[-1])
:lua for item in l() do print(item) end


  1. Dict userdata lua-dict

Similarly to list userdata, dict userdata represent vim dictionaries; since dictionaries are also objects, references are kept between Lua and Vim. A dict “d” has the following properties:


o "#d" is the number of items in dict "d", equivalent to "len(d)"
    in Vim.
o "d.key" or "d['key']" returns the value at entry "key" in "d".
    To modify the entry at this key, simply do "d.key = newvalue"; in
    particular, "d.key = nil" removes the entry from "d".
o "d()" returns an iterator for "d" and is equivalent to "items(d)" in


:let d = {'n':10}
:lua d = vim.eval('d') -- same 'd'
:lua print(d, d.n, #d)
:let d.self = d
:lua for k, v in d() do print(d, k, v) end
:lua d.x = math.pi
:lua d.self = nil -- remove entry
:echo d


  1. Funcref userdata lua-funcref

Funcref userdata represent funcref variables in Vim. Funcrefs that were defined with a “dict” attribute need to be obtained as a dictionary key in order to have “self” properly assigned to the dictionary (see examples below.) A funcref “f” has the following properties:


o "#f" is the name of the function referenced by "f"
o "f(...)" calls the function referenced by "f" (with arguments)


:function I(x)
:  return a:x
:  endfunction
:let R = function('I')
:lua i1 = vim.funcref('I')
:lua i2 = vim.eval('R')
:lua print(#i1, #i2) -- both 'I'
:lua print(i1, i2, #i2(i1) == #i1(i2))
:function Mylen() dict
:  return len(self.data)
:  endfunction
:let mydict = {'data': [0, 1, 2, 3]}
:lua d = vim.eval('mydict'); d.len = vim.funcref('Mylen')
:echo mydict.len()
:lua l = d.len -- assign d as 'self'
:lua print(l())


  1. Buffer userdata lua-buffer

Buffer userdata represent vim buffers. A buffer userdata “b” has the following properties and methods:


o "b()" sets "b" as the current buffer.
o "#b" is the number of lines in buffer "b".
o "b[k]" represents line number k: "b[k] = newline" replaces line k
    with string "newline" and "b[k] = nil" deletes line k.
o "b.name" contains the short name of buffer "b" (read-only).
o "b.fname" contains the full name of buffer "b" (read-only).
o "b.number" contains the position of buffer "b" in the buffer list


o "b:insert(newline[, pos])" inserts string "newline" at (optional)
    position "pos" in the buffer. The default value for "pos" is
    "#b + 1". If "pos == 0" then "newline" becomes the first line in
    the buffer.
o "b:next()" returns the buffer next to "b" in the buffer list.
o "b:previous()" returns the buffer previous to "b" in the buffer
o "b:isvalid()" returns 'true' (boolean) if buffer "b" corresponds to
    a "real" (not freed from memory) Vim buffer.


:lua b = vim.buffer() -- current buffer
:lua print(b.name, b.number)
:lua b[1] = "first line"
:lua b:insert("FIRST!", 0)
:lua b[1] = nil -- delete top line
:lua for i=1,3 do b:insert(math.random()) end
:3,4lua for i=vim.lastline,vim.firstline,-1 do b[i] = nil end
:lua vim.open"myfile"() -- open buffer and set it as current
function! ListBuffers()
lua << EOF
local b = vim.buffer(true) -- first buffer in list
while b ~= nil do
    print(b.number, b.name, #b)
    b = b:next()


  1. Window userdata lua-window

Window objects represent vim windows. A window userdata “w” has the following properties and methods:


o "w()" sets "w" as the current window.
o "w.buffer" contains the buffer of window "w" (read-only).
o "w.line" represents the cursor line position in window "w".
o "w.col" represents the cursor column position in window "w".
o "w.width" represents the width of window "w".
o "w.height" represents the height of window "w".


o "w:next()" returns the window next to "w".
o "w:previous()" returns the window previous to "w".
o "w:isvalid()" returns 'true' (boolean) if window "w" corresponds to
    a "real" (not freed from memory) Vim window.


:lua w = vim.window() -- current window
:lua print(w.buffer.name, w.line, w.col)
:lua w.width = w.width + math.random(10)
:lua w.height = 2 * math.random() * w.height
:lua n,w = 0,vim.window(true) while w~=nil do n,w = n + 1,w:next() end
:lua print("There are " .. n .. " windows")


  1. The luaeval function lua-luaeval lua-eval

The (dual) equivalent of “vim.eval” for passing Lua values to Vim is “luaeval”. “luaeval” takes an expression string and an optional argument and returns the result of the expression. It is semantically equivalent in Lua to:

local chunkheader = "local _A = select(1, ...) return "
function luaeval (expstr, arg)
    local chunk = assert(loadstring(chunkheader .. expstr, "luaeval"))
    return chunk(arg) -- return typval

< Note that “_A” receives the argument to “luaeval”. Lua numbers, strings, and list, dict, and funcref userdata are converted to their Vim respective types, while Lua booleans are converted to numbers. An error is thrown if conversion of any of the remaining Lua types, including userdata other than lists, dicts, and funcrefs, is attempted.

Examples: >

:echo luaeval('math.pi')
:lua a = vim.list():add('newlist')
:let a = luaeval('a')
:echo a[0] " 'newlist'
:function Rand(x,y) " random uniform between x and y
:  return luaeval('(_A.y-_A.x)*math.random()+_A.x', {'x':a:x,'y':a:y})
:  endfunction
:echo Rand(1,10)