runit.nvim

Neovim plugin for one-click code execution

INTRODUCTION

This plugin makes running code in your current buffer lightning fast and incredibly simple. Many popular languages like C, Java, Python, Go, JS, Perl, Shell, Lua, R, Rmarkdown, etc. are supported.

Usage

Command	Default key mapping	Description
:RunBuf	<F4>	Run the code
:RunBufArgs	<F16> (SHIFT+<F4> or <S-F4>)	Run the code with arguments

Installation

Using lazy.nvim

  {
    'rltyty/runit.nvim',
    config = function()
      require("runit").setup()
    end
  },

CONFIGURATION

• Default options

-- Default options
M.opts = {
  key = true,             -- false: disable key mapping
  run_key = "<F4>",
  run_args_key = "<F16>", -- run with args input. <F-16> instead of <S-F4>
  src_prefix = "src",
  test_prefix = "src",
}

• Disable key mapping,

  require("runit").setup({
    key = false,
  })

• Change key mapping,

  require("runit").setup({
    run_key = "<F2>",
    run_args_key = "<F14>",
  })

• Project specific settings

Create a .nvim.lua (See h: exrc) under the project root directory.

  require("runit").setup({
    run_key = "<F2>",
    src_prefix = "source"
    test_prefix = "test"
  })

FAQ

Multi-process Output Order Problem

Runit runs programs in Neovim's command mode, and sometimes you may find that the output order is "unexpected". For example,

Suppose you run a C program like this — you expect the date output to come after the welcome message, but it doesn't.

...
printf("Main process says hi\n");
system("date");
// do some other stuff
...

• Running in Neovim

:!./Debug/test/a.out
Fri Aug 15 14:33:00 CST 2025
Main process says hi

• Running in a terminal,

> ./Debug/test/a.out
Main process says hi
Fri Aug 15 14:42:55 CST 2025

Reason for the Discrepancy: When executed in Neovim, the process's stdout stream is connected to a pipe, not a terminal (TTY). The C standard library chooses the buffer mode of the stream based on the file type. TTY -> line-buffered, otherwise -> fully-buffered. Therefore, in Neovim, the output is fully-buffered, whereas in a terminal it is line-buffered.

In the program above, although the printf message ends with \n (which normally triggers a unbuffered write(2) system call immediately in a terminal), in Neovim, it will not be written until either fflush(stdout) is called explicitly or exit() automatically flushes and closes streams at program termination.

Meanwhile, system("date") spawns (fork() + exec()) a child process to run the date command. The child inherits, during fork(), a copy of its parent's open file descriptors, including STDOUT_FILENO, which still points to the same file table entry and further the same pipe. The child also inherits the parent's file streams and their buffers, so the child's stdout buffer also contains "Main process says hi". However, when exec() loads the date program, the child gets fresh process image with new program date, fresh file streams, empty buffers. After date is done, it exit()s with all its file streams getting flush()ed and close()d, so we can see the date output right way. As long as the parent finishes after the child, the output order will appear "unexpected". In reality, it is exactly what buffering rules dictate. It's also the case when you redirect the output to a file.

> ./Debug/test/a.out > log
> cat log
Sat Aug 16 12:16:05 CST 2025
Main process says hi

If you do need the "expected" order, either run the program in a terminal or change the code:

• Option 1 : Explicit fflush

printf("Main process says hi\n");
fflush(stdout);
system("date");

• Option 2: Disable buffer for stdout

setvbuf(stdout, NULL, _IONBF, 0);