将系统命令的结果绑定到Haskell中的变量 [英] Binding the result of a system command to a variable in Haskell

问题描述

如何在Haskell 和中运行系统命令，将其结果（即标准输出）绑定到变量？在伪哈斯克尔中，我正在寻找如下内容：

  import System.Process 
 
 main = do输出<  -  callCommandecho hi
 putStrLn输出 - 结果：hi
  

这不起作用。是否有类似的东西？

解决方案

以下是一些工作代码：

  import System.Process 
 $ b $ main :: IO（）
 main = do 
 let stdin'=
（errCode，stdout'，stderr'）<  -  readProcessWithExitCodeecho[hi] stdin'
 putStrLn $stdout：++ stdout'
 putStrLn $stderr：++ stderr'
 putStrLn $errCode：++ show errCode 
  

Carsten指出，可以使用readProcess，但我更喜欢这个版本，因为任何严重的用法，你很快会对你的命令为什么会失败而感到困惑（如果你在命令行中运行，当然会显示stdout和stderr）。

How does one run a system command in Haskell and bind it's result (i.e., standard output) to a variable? In pseudo-haskell I'm looking for something like the following:

import System.Process

main = do output <- callCommand "echo hi"
          putStrLn output -- result: "hi"

This does not work. Is there something similar that does?

解决方案

Here is some working code:

import System.Process

main :: IO ()
main = do
  let stdin' = ""
  (errCode, stdout', stderr') <- readProcessWithExitCode "echo" ["hi"] stdin'
  putStrLn $ "stdout: " ++ stdout'
  putStrLn $ "stderr: " ++ stderr'
  putStrLn $ "errCode: " ++ show errCode

As Carsten notes, you can use readProcess, but I prefer this version because with any serious usage, you will soon be very confused as to why your command is silently failing (if you run in the command line, both stdout and stderr are, of course, shown).

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