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copied!<p>First, with some exceptions, redirections generally occur at the point they are written. They are removed from the command-and-argument sequence; only the remaining, non-redirection, words participate. Thus:</p> <pre><code>3>&1 foo 1>&2 arg1 2>&3 arg2 3>&- arg3 </code></pre> <p>runs <code>foo arg1 arg2 arg3</code> with stdout and stderr swapped, because:</p> <ol> <li><code>3>&1</code> makes a copy (more precisely, a <code>dup2</code>) of fd 1 (stdout) on fd 3</li> <li><code>1>&2</code> makes a copy of fd 2 (stderr) on fd 1 (so now stdout and stderr both go wherever they were going)</li> <li><code>2>&3</code> makes a copy of fd 3 (saved original stdout) on fd 2 (stderr)</li> <li><code>3>&-</code> closes fd 3.</li> </ol> <p>(The notable exception is that piped output "happens first", even though the pipe symbol is at the end of the simple-command part.)</p> <p>Second, as pje noted, <code>time</code> is a bash built-in. <code>time foo</code> runs the command, then prints the time summary to bash's stderr. The <code>time</code> keyword is effectively removed first, then the remaining command sequence is handled as usual. (This applies even if the command is a pipeline: <code>time</code> times the entire pipeline.)</p> <p>In this case, the command sequence is one simple command, with redirections:</p> <pre><code>2>&1 sh 2>&1 -c ... > file </code></pre> <p>Each redirection happens at the point it is written, and the remaining sequence is:</p> <pre><code>sh -c ... </code></pre> <p>The redirections are:</p> <ol> <li>send stderr to wherever stdout is currently going</li> <li>send stderr to stdout, again (this has no new effect)</li> <li>send stdout to <code>file</code>.</li> </ol> <p>so <code>sh -c</code> is run with its stderr going to your stdout, and its stdout going to file <code>file</code>. As you note, <code>dd</code> prints its output to (its) stderr, which is <code>sh -c ...</code>'s stderr, which is your stdout.</p> <p>If you run:</p> <pre><code>time 2>file dd if=/dev/zero of=ddfile bs=512 count=125 </code></pre> <p>you will get <code>time</code>'s stderr output on your stderr (e.g., screen), and <code>dd</code>'s stderr on file <code>file</code>. (This happens no matter how far right you slide the <code>2>file</code> part, as long as it remains part of the simple-command.)</p> <p>If you try:</p> <pre><code>2>file time ... </code></pre> <p>you will find <code>time</code>'s output redirected, but this defeats the built-in <code>time</code> entirely, running <code>/usr/bin/time</code> instead. To get bash's built-in to fire, <code>time</code> has to be up front. You can make a sub-shell:</p> <pre><code>(time ...) 2>file </code></pre> <p>or a sub-block as <a href="https://stackoverflow.com/a/18753722/1256452">pje illustrated</a>:</p> <pre><code>{ time ...; } 2>file </code></pre> <p>(the syntax is clumsier with the sub-block as white space and/or semicolons are needed, but it avoids a <code>fork</code> system call).</p>

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