Repl like experience with simple lua script.

redir.lua

-- TODO: split things into small functions

-- reference
-- https://gist.github.com/romainl/eae0a260ab9c135390c30cd370c20cd7
local function Redir(opts)
  local cmd = opts.fargs[1]
  local rng = opts.range
  local line1 = opts.line1 - 1
  local line2 = opts.line2
  local vertical = opts.smods.vertical
  line2 = line1 == line2 and line1 + 1 or line2

  local output

  local Job = require("plenary.job")
  if string.match(cmd, "^!") then
    cmd = vim.fn.split(cmd)

    local command = cmd[1]:sub(2)
    local args = {}
    for i, t in ipairs(cmd) do
      if i ~= 1 then
        table.insert(args, t)
      end
    end

    if rng == 0 then
      -- NOTE: no input given, call command
      Job:new({
        command = command,
        args = args,
        on_exit = function(j, _)
          output = j:result()
        end,
      }):sync()
    else
      -- NOTE: setup input in temp file
      local lines = vim.api.nvim_buf_get_lines(0, line1, line2, false)
      local input = vim.fn.join(lines, "\n")
      local file = vim.fn.tempname()
      local f = io.open(file, "w+")
      if not f then
        return
      end
      f:write(input)
      f:close()

      table.insert(args, file)

      Job:new({
        command = command,
        args = args,
        on_exit = function(j, _)
          output = j:result()
        end,
      }):sync()
    end
  else
    -- NOTE: vim command
    vim.cmd("redir => output")
    vim.cmd(cmd)
    vim.cmd("redir END")
    output = vim.fn.split(vim.g.output, "\n")
  end

  local buf = vim.api.nvim_create_buf(false, true)
  vim.api.nvim_buf_set_lines(buf, 0, 0, false, output)
  vim.api.nvim_open_win(buf, true, {
    vertical = vertical,
  })
end

vim.api.nvim_create_user_command("Mes", function()
  vim.cmd("Redir mes")
end, {})
vim.cmd([[cabbrev M Mes]])

vim.api.nvim_create_user_command("Redir", Redir, {
  nargs = 1,
  complete = "command",
  range = true,
})
vim.cmd([[cabbrev R Redir]])

local interepters = {
  python = "python",
  sh = "bash",
  bash = "bash",
  fish = "fish",
  lua = "luajit",
}

local function redir(range)
  return function()
    local line = vim.fn.getline(1)
    local interepter = string.match(line, "^#!(.*)")

    if not interepter then
      local ft = vim.o.ft
      interepter = interepters[ft]
    end

    if interepter then
      vim.cmd(string.format("silent %sRedir !%s", range, interepter))
    else
      -- FIXME: setcmdline not work
      vim.fn.setcmdline(string.format("silent %sRedir !", range))
    end
  end
end

vim.api.nvim_create_user_command("RedirEvalLine", redir("."), {})
vim.api.nvim_create_user_command("RedirEvalFile", redir("%"), {})
-- FIXME: not work well
-- vim.api.nvim_create_user_command("RedirEvalRange", redir("'<,'>"), {})

redir.md

Some documentations needed, WIP.