using git to recreate historic builds

[John Vasileff]

Just learned something useful about git that I thought I’d share.

For a while, I’ve been using commands like:

git checkout 'origin/master@{2015-03-26}’
git checkout 'origin/master@{7 hours ago}’

to recreate historic builds across multiple repositories.

But, as it turns out, the time specification in those commands refers to *the state of the branch in your local repository at that time*, and not necessarily commit timestamps. So, if you went a month without fetching `origin/master`, and then fetched, “1 hour ago” would yield the same result as “20 days ago”.

It may be useful to recreate *your* repository at a point in time. But it may also be confusing. Fortunately, there is a way to discover commits based on the commit timestamp, and checkout based on that:

git checkout `git rev-list -n 1 --before="2015-03-26" origin/master`
git checkout `git rev-list -n 1 --before="7 hours ago" origin/master`

This still isn’t perfect since not all commits are immediately pushed (there’s no way to recreate the state of *github’s* repository at a point in time). But it should work pretty well.

John

[Gavin King]

Hah! Thanks, that's very useful!

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Gavin King
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