How to rename an annotated tag in Git

Question

How can an existing annotated tag be renamed in Git?

I have almost a hundred tags representing version numbers on a repository, and each tag is annotated with a useful description about what was changed that version. I'd like to change the naming style I've used for these tags, and recording the tag message, deleting the tag, and recreating it with the old message and a new name would be a nightmare to do manually for almost a hundred tags. A script or a series of git commands to do this would be useful for automation.

Answer 1

The bad news is that the name of an annotated tag object is embedded inside that annotated tag object. So if you want to be totally thorough, you'll need to replace those tag objects:

• If they're signed tags you will need to regenerate them with new signatures.

• Otherwise, it's possible to copy the tag objects to new tag objects, with the systematic name changes you'd like to make. The filter-branch command does this, for instance. (It's a bit ugly since you have to use some low level plumbing commands; there's no easy convenient method. But see below.)

The good news is that there's no absolute requirement that you use the "correct" annotated tag along with a lightweight tag. That is, an annotated tag is actually a pair of entities: a lightweight tag (with some name that's simply an entry in the refs/tags/ name-space), along with an annotated tag object (in the repository itself) that normally has the same name in its tag field. But you can make a new lightweight tag that points to the existing annotated tag object, then optionally delete the original lightweight tag:

$ git cat-file -p v2.5.0 | sed 's/@/ /'
object a17c56c056d5fea0843b429132904c429a900229
type commit
tag v2.5.0
tagger Junio C Hamano <gitster pobox.com> 1438025401 -0700

Git 2.5
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$ git rev-parse v2.5.0
8d1720157c660d9e0f96d2c5178db3bc8c950436
$ git tag silly v2.5.0
$ git rev-parse silly
8d1720157c660d9e0f96d2c5178db3bc8c950436
$ git tag -d v2.5.0
Deleted tag 'v2.5.0' (was 8d17201)
$ git for-each-ref refs/tags/silly
8d1720157c660d9e0f96d2c5178db3bc8c950436 tag    refs/tags/silly

(I restored the old tag and deleted the "silly" version after this, so it's not terribly thoroughly tested, but it didn't blow up at least.)

To automate either copying the tags, or re-creating the tags (with or without signatures), simply use git for-each-ref to find all the old tags, and use the resulting names to make the new tags. Use git cat-file -p to pretty-print the existing tag for modifying to make the new tag, or simply make the new tag pointing to the existing tag object. After printing the tag (to a pipe or file) you can edit it with sed or some other programmable editor, and feed the result to git tag -F as an input file, or to git mktag to create a tag object, feeding the resulting SHA-1 to git tag to make the corresponding lightweight tag.

(Note: if you've gotten partway through writing a bash script to do all this, and just need help to finish it up or correct some issue(s) with it, post the script-so-far.)