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    <p>I'm assuming you want to still see STDERR and STDOUT on the terminal. You could go for Josh Kelley's answer, but I find keeping a <code>tail</code> around in the background which outputs your log file very hackish and cludgy. Notice how you need to keep an exra FD and do cleanup afterward by killing it and technically should be doing that in a <code>trap '...' EXIT</code>.</p> <p>There is a better way to do this, and you've already discovered it: <code>tee</code>.</p> <p>Only, instead of just using it for your stdout, have a tee for stdout and one for stderr. How will you accomplish this? Process substitution and file redirection:</p> <pre><code>command &gt; &gt;(tee -a stdout.log) 2&gt; &gt;(tee -a stderr.log &gt;&amp;2) </code></pre> <p>Let's split it up and explain:</p> <pre><code>&gt; &gt;(..) </code></pre> <p><code>&gt;(...)</code> (process substitution) creates a FIFO and lets <code>tee</code> listen on it. Then, it uses <code>&gt;</code> (file redirection) to redirect the STDOUT of <code>command</code> to the FIFO that your first <code>tee</code> is listening on.</p> <p>Same thing for the second:</p> <pre><code>2&gt; &gt;(tee -a stderr.log &gt;&amp;2) </code></pre> <p>We use process substitution again to make a <code>tee</code> process that reads from STDIN and dumps it into <code>stderr.log</code>. <code>tee</code> outputs its input back on STDOUT, but since its input is our STDERR, we want to redirect <code>tee</code>'s STDOUT to our STDERR again. Then we use file redirection to redirect <code>command</code>'s STDERR to the FIFO's input (<code>tee</code>'s STDIN).</p> <p>See <a href="http://mywiki.wooledge.org/BashGuide/InputAndOutput" rel="noreferrer">http://mywiki.wooledge.org/BashGuide/InputAndOutput</a></p> <p>Process substitution is one of those really lovely things you get as a bonus of choosing <code>bash</code> as your shell as opposed to <code>sh</code> (POSIX or Bourne).</p> <hr> <p>In <code>sh</code>, you'd have to do things manually:</p> <pre><code>out="${TMPDIR:-/tmp}/out.$$" err="${TMPDIR:-/tmp}/err.$$" mkfifo "$out" "$err" trap 'rm "$out" "$err"' EXIT tee -a stdout.log &lt; "$out" &amp; tee -a stderr.log &lt; "$err" &gt;&amp;2 &amp; command &gt;"$out" 2&gt;"$err" </code></pre>
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    1. POHow do I write stderr to a file while using "tee" with a pipe?
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    1. POHow do I write stderr to a file while using "tee" with a pipe?
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    1. COI tried to get process substitution to work but wasn't doing it right. This is a much simpler solution than mine. Thanks.
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      1. USJosh Kelley
    2. COI tried this: `$ echo "HANG" > >(tee stdout.log) 2> >(tee stderr.log >&2)` which works, but waits for input. Is there a simple reason why this happens?
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      1. USJustin
    3. CO@Justin: I don't know what you mean by "waits for input". The command you gave does not "wait" for anything with me.
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