Question

Here is the man page for git show-ref -d . They also have an example at the bottom. Still I am not able to understand what dereference does?

Answer 1

In Git, a "normal" (annotated, not lightweight) tag is an object unto itself, containing metadata and the SHA1 of the object it tags. Chapter 10.2 Git Internals – Git Objects in the Git community book has an illustration of the object model:

^{Legend: yellow – commit object, blue/green – tree object, white – blob object}

So, when you use git show-ref on a normal tag, it will normally give you information about the tag object. With the -d/--dereference option, it will dereference the tag into the object the tag refers to, and provide information about it instead.

And a note on lightweight vs. annotated tags, in case you aren’t aware of that: a lightweight tag is created by using git tag <tag name> (i.e. without any of the metadata-providing options like -a, -s, or -u). It’s not a tag object at all, just a Git reference pointing straight to the object you’ve tagged. If you provide one of those options, you’re attaching metadata to the tag, so Git creates a tag object to hold that.