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    <p>I don't think that your assertion above that the second command will fail if the first fails is true. If <code>mv dir1 dir1_backup</code> fails, then dir1 will still exist, and <code>mv dir2 dir1</code> will make dir2 a subdirectory of dir1. Also, since you are passing <code>-f</code> to <code>rm</code> in the third command, it will silently fail to delete a non-existant directory.</p> <p>For reference, three bash operators (assuming bash here) and what they do:</p> <ul> <li>; simply executes the following command after the first exits, regardless of the exit status.</li> <li>&amp;&amp; executes the following command only if the previous command exited cleanly (ie, had an exit status of 0.)</li> <li>|| executes the following command only if the previous command exited uncleanly (ie, had a non-zero exit code.)</li> </ul> <p>If you want each command's execution to be dependent upon the previous command's successful execution, then you might want to consider something like the following:</p> <p><pre><code> mv dir1 dir1_backup && mv dir2 dir1 && rm -rf dir1_backup</code></pre></p> <p>If the moving of a directory is a failure mode you expect, then it may be reasonable to test the return value of the move or to test for the existence of the expected directory before proceeding to remove the old directory contents. If the test fails, then move the old directory contents back. The overall operation will have failed, but at least you will not be in an invalid state. For example:</p> <p><pre><code> mv dir1 dir1_backup &amp;&amp; \ mv dir2 dir1 &amp;&amp; \ rm -rf dir1_backup || mv dir1_backup dir1</code></pre></p> <p>Since we know that <code>&amp;&amp;</code> executes the following command only if the previous command exits successfully, <code>mv dir2 dir1</code> will only execute if <code>mv dir1 dir1_backup</code> succeeds.</p> <p>Further, <code>rm -rf dir1_backup</code> will only execute if the move of dir2 to dir1 succeeds. However, if the last exit code (the code returned by <code>mv dir2 dir1</code> if it has failed) is non-zero, the <code>||</code> operator causes <code>mv dir1_backup dir1</code> to execute.</p> <p>Hope that helps! Let me know if it needs clarification.</p>
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    1. POUNIX atomically swap or replace directories?
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    1. COcfunk, thanks for clearing that up. I thought that ; and && did the opposite of what they actually do. Your solution is closer to what I want, but there is a corner case. First command completes successfully. Second command fails, triggering the last command. (mv dir1_backup dir1) Imagine if the LAST command fails. I am still left with in invalid state: dir1 does not exist.
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    2. COIf you are able to rename the directory in the first case, what is the failure mode you expect to prevent you from moving it back? If that's expected, you might want to investigate the use of symlinks instead of moving directories around. If possible, it might be best to have the application accessing the directory look at the new location and not worry about shuffling directories at all.
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