git tag 对象的格式是什么以及如何计算它的 SHA? [英] What is the format of a git tag object and how to calculate its SHA?

问题描述

我熟悉 Git 如何为文件(blob)创建 SHA1 哈希，但不熟悉它们是如何为标签创建的对象.我假设它们是，如果我创建一个带注释的标签，但配方是什么?我如何在 Git 之外复制它(例如，在 Perl 或 Python 中)?

I am familiar with how Git creates SHA1 hashes for files (blobs), but not how they are created for tag objects. I assume they are, if I create an annotated tag, but what is the recipe? And how might I replicate it outside of Git (e.g., in Perl or Python)?

推荐答案

模式基本是:

sha1("tag " + datasize + "" + data)

其中data 是git cat-file 的输出.可以通过将输出通过管道传输到 git-hash-object 来产生这一点，如下所示:

Where data is the output of git cat-file. One can produce this by piping that output to git-hash-object like so:

git cat-file tag v0.30 | git hash-object -t tag --stdin

等价的 perl one-liner 是:

And the equivalent a perl one-liner is:

git cat-file tag v0.30 | perl -MDigest::SHA1 -E '$/=undef;$_=<>;say Digest::SHA1->new->add("tag ".length()."".$_)->hex digest'

似乎可以对任何类型的对象执行相同的操作，只需将 "tag " 替换为正确的对象名称:"blob ", >树"，或提交".

It seems that one can do this same thing with any of the types objects simply by replacing "tag " with the proper object name: "blob ", "tree ", or "commit ".

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