你如何用lua构建一个读写管道？

Question

我想做相当于:

foo=$(echo "$foo"|someprogram)

在lua中 - 也就是说,我有一个包含一堆文本的变量,我想通过一个过滤器运行它(在python中实现它).

任何提示？

补充:真的很想不使用临时文件

Answer 1

只要你的Lua支持io.popen，这个问题就很容易了。解决方案与您概述的完全一样，只是$(...)您不需要这样的功能：

function os.capture(cmd, raw)
  local f = assert(io.popen(cmd, 'r'))
  local s = assert(f:read('*a'))
  f:close()
  if raw then return s end
  s = string.gsub(s, '^%s+', '')
  s = string.gsub(s, '%s+$', '')
  s = string.gsub(s, '[\n\r]+', ' ')
  return s
end

然后你可以打电话

local foo = ...
local cmd = ("echo $foo | someprogram"):gsub('$foo', foo)
foo = os.capture(cmd)

我一直在做这样的事情。这是用于形成命令的相关有用函数：

local quote_me = '[^%w%+%-%=%@%_%/]' -- complement (needn't quote)
local strfind = string.find

function os.quote(s)
  if strfind(s, quote_me) or s == '' then
    return "'" .. string.gsub(s, "'", [['"'"']]) .. "'"
  else
    return s
  end
end

Answer 2

我在尝试做同样的事情时偶然发现了这篇文章，但从未找到好的解决方案，请参阅下面的代码以了解我如何解决我的问题。此实现允许用户访问 stdin、stdout、stderr 并获取返回状态代码。简单的管道调用需要一个简单的包装器。

require("posix")

--
-- Simple popen3() implementation
--
function popen3(path, ...)
    local r1, w1 = posix.pipe()
    local r2, w2 = posix.pipe()
    local r3, w3 = posix.pipe()

    assert((w1 ~= nil or r2 ~= nil or r3 ~= nil), "pipe() failed")

    local pid, err = posix.fork()
    assert(pid ~= nil, "fork() failed")
    if pid == 0 then
        posix.close(w1)
        posix.close(r2)
        posix.dup2(r1, posix.fileno(io.stdin))
        posix.dup2(w2, posix.fileno(io.stdout))
        posix.dup2(w3, posix.fileno(io.stderr))
        posix.close(r1)
        posix.close(w2)
        posix.close(w3)

        local ret, err = posix.execp(path, unpack({...}))
        assert(ret ~= nil, "execp() failed")

        posix._exit(1)
        return
    end

    posix.close(r1)
    posix.close(w2)
    posix.close(w3)

    return pid, w1, r2, r3
end

--
-- Pipe input into cmd + optional arguments and wait for completion
-- and then return status code, stdout and stderr from cmd.
--
function pipe_simple(input, cmd, ...)
    --
    -- Launch child process
    --
    local pid, w, r, e = popen3(cmd, unpack({...}))
    assert(pid ~= nil, "filter() unable to popen3()")

    --
    -- Write to popen3's stdin, important to close it as some (most?) proccess
    -- block until the stdin pipe is closed
    --
    posix.write(w, input)
    posix.close(w)

    local bufsize = 4096
    --
    -- Read popen3's stdout via Posix file handle
    --
    local stdout = {}
    local i = 1
    while true do
        buf = posix.read(r, bufsize)
        if buf == nil or #buf == 0 then break end
        stdout[i] = buf
        i = i + 1
    end

    --
    -- Read popen3's stderr via Posix file handle
    --
    local stderr = {}
    local i = 1
    while true do
        buf = posix.read(e, bufsize)
        if buf == nil or #buf == 0 then break end
        stderr[i] = buf
        i = i + 1
    end

    --
    -- Clean-up child (no zombies) and get return status
    --
    local wait_pid, wait_cause, wait_status = posix.wait(pid)

    return wait_status, table.concat(stdout), table.concat(stderr)
end

--
-- Example usage
--
local my_in = io.stdin:read("*all")
--local my_cmd = "wc"
--local my_args = {"-l"}
local my_cmd = "spamc"
local my_args = {} -- no arguments
local my_status, my_out, my_err = pipe_simple(my_in, my_cmd, unpack(my_args))

-- Obviously not interleaved as they would have been if printed in realtime
io.stdout:write(my_out)
io.stderr:write(my_err)

os.exit(my_status)

Answer 3

Lua 标准库中没有任何内容允许这样做。

这里深入探讨了正确进行双向通信的难点，以及提出的解决方案：

如果可能，将流的一端（输入或输出）重定向到一个文件。IE：

fp = io.popen("foo >/tmp/unique", "w")
fp:write(anything)
fp:close()
fp = io.open("/tmp/unique")
x = read("*a")
fp:close()

您可能对这个扩展感兴趣，它向os和io命名空间添加函数，使与子进程的双向通信成为可能。

Answer 4

啊哈，一个可能更好的解决方案：

require('posix')
require('os')
require('io')

function splat_popen(data,cmd)
   rd,wr = posix.pipe()
   io.flush()
   child = posix.fork()
   if child == 0 then
      rd:close()
      wr:write(data)
      io.flush()
      os.exit(1)
   end
   wr:close()

   rd2,wr2 = posix.pipe()
   io.flush()
   child2 = posix.fork()
   if child2 == 0 then
      rd2:close()
      posix.dup(rd,io.stdin)
      posix.dup(wr2,io.stdout)
      posix.exec(cmd)
      os.exit(2)
   end
   wr2:close()
   rd:close()

   y = rd2:read("*a")
   rd2:close()

   posix.wait(child2)
   posix.wait(child)

   return y
end

munged=splat_popen("hello, world","/usr/games/rot13")
print("munged: "..munged.." !")