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copied!<p>I have a similar problem and I figured out it.</p> <p>I want to detect forced update within hook script in remote (bare) repository, So my answer might not be suitable for original question, but I hope to be useful my answer for future visitors.</p> <hr> <h1>How to detect forced update or not from in Git hooks script</h1> <p><a href="https://github.com/kyanny/git-hooks-detect-force-update" rel="nofollow noreferrer">https://github.com/kyanny/git-hooks-detect-force-update</a></p> <p>This is a sample git pre-receive hook script for learning about how to detect forced update.</p> <h2>Conclusion</h2> <pre><code>$ git rev-list oldrev ^newrev </code></pre> <h2>How to test</h2> <pre><code>$ rake -T rake forced_push # git hooks test detect forced update rake normal_push # git hooks test </code></pre> <h2>Step-by-Step introduction</h2> <p>Firstly, I describe a syntax of <a href="http://git-scm.com/docs/git-rev-list" rel="nofollow noreferrer">git-rev-list(1)</a>.</p> <p>In this case, we assume within a Git working repository that has this straight history.</p> <pre><code>1 --- 2 --- O --- X --- 3 --- 4 --- N </code></pre> <p>General usage of <code>git-rev-list</code> is below.</p> <pre><code>$ git rev-list N </code></pre> <p>This command will show all of commits reachable from commit N (note: <code>git-rev-list</code> shows commits <em>reverse chronological order</em>)</p> <p><code>git-rev-list</code> accepts multiple arguments.</p> <pre><code>$ git rev-list N O </code></pre> <p>This command will show same output as <code>git rev-list N</code>, because commit O is an ancestor of commit N.</p> <p>Then, <code>git-rev-list</code> allows you to exclude commits from output.</p> <pre><code>$ git rev-list N ^O </code></pre> <p>^O means that to exclude commits reachable from O, so this command will show N, 4, 3, X (note: O is excluded)</p> <hr> <p>Since we are learned about <code>git-rev-list</code>, I describe a case about forced update occured.</p> <p>In this case, we assume within a Git working repository that has this complex history.</p> <pre><code>* --- B --- * --- O ($oldrev) \ * --- X --- * --- N ($newrev) </code></pre> <ol> <li>In old tree, we had 4 commits (*, B, *, O) and pushed them to remote.</li> <li>We checkout a new branch from commit B, it's new tree.</li> <li>In new tree, we had 4 commits (*, X, *, N) and pushed them to remote with --force option!</li> </ol> <p>When pushed, hook pre-receive script invoked with standard input. The format of stdin parameter is described at <a href="http://git-scm.com/docs/githooks" rel="nofollow noreferrer">githooks(5)</a>.</p> <p>Typically, we extract two commit object sha1 from stdin - oldrev and newrev. oldrev is <em>HEAD of old tree</em>, newrev is <em>HEAD of new tree</em>.</p> <p>In this situation, we can detect forced push by <code>git-rev-list</code> output.</p> <p><code>git rev-list oldrev ^newrev</code> shows the commits reachable from oldrev but not reachable from newrev. This shows the commits <em>existed only old tree</em>. If this command show any commits, old tree was replaced with new tree, so forced update was occured. This is what we want!</p> <p>If this command show none of commits, new tree was normally updated, so forced update was not occured. Simply.</p> <h2>See Also</h2> <ul> <li><a href="http://git-scm.com/docs/git-rev-list" rel="nofollow noreferrer">git-rev-list(1)</a></li> <li><a href="http://git.gnus.org/gnus.git/hooks/post-receive-email" rel="nofollow noreferrer">Git hook example: post-receive-email</a></li> <li><a href="https://stackoverflow.com/questions/10319110/how-to-detect-a-forced-update">git - How to detect a forced update - Stack Overflow</a></li> <li><a href="https://stackoverflow.com/questions/9210957/git-hook-to-detect-push-mirror">githooks - Git hook to detect push --mirror - Stack Overflow</a></li> </ul>

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