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POHaskell: System.Process merge stdout and stderr
 

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  1. POHaskell: System.Process merge stdout and stderr
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    <p>I want to invoke a process from within a haskell program and capture stdout as well as stderr. </p> <p>What I do:</p> <pre><code>(_, stdout, stderr) &lt;- readProcessWithExitCode "command" [] "" </code></pre> <p>The problem: This way, stdout and stderr are captured separately, however I want the messages to appear in the right place (otherwise I would simply <code>stdout ++ stderr</code> which separates error messages from their stdout counterparts).</p> <p>I do know that I could achieve this if I'd pipe the output into a file, i.e.</p> <pre><code>tmp &lt;- openFile "temp.file" ... createProcess (proc "command" []) { stdout = UseHandle tmp, stderr = UseHandle tmp } </code></pre> <p>So my current workaround is to pipe outputs to a tempfile and read it back in. However I'm looking for a more direct approach.</p> <p>If I was on unix for sure I'd simply invoke a shell command á la</p> <pre><code>command 2&gt;&amp;1 </code></pre> <p>and that's it. However, I'd like to have this as portable as possible.</p> <p>What I need this for: I've built a tiny haskell cgi script (just to play with it) which invokes a certain program and prints the output. I want to html-escape the output, thus I can't simply pipe it to stdout.</p> <p>I was thinking: Maybe it's possible to create an in-memory-handle, like a PipedInputStream/PipedOutputStream in Java, or ArrayInputStream/ArrayOutputStream which allows for processing IO streams within memory. I looked around for a function <code>:: Handle</code> on hoogle, but did not find anything.</p> <p>Maybe there is another Haskell module out there which allows me to merge two streams?</p>
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    1. COPerhaps [`createPipe`](http://hackage.haskell.org/packages/archive/unix/latest/doc/html/System-Posix-IO-ByteString.html#v:createPipe) and [`fdToHandle`](http://hackage.haskell.org/packages/archive/unix/latest/doc/html/System-Posix-IO-ByteString.html#v:fdToHandle) will help.
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      1. USDaniel Wagner
 

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