What does the "at" @ sign/symbol/character mean in Git?
git
Solution
As of Git version 1.8.5, the at-sign `@`, without a leading branch/reference name and ordinal `{n}` suffix like `HEAD@{1}` and `master@{1}`, is just a synonym/alias/shortcut for the special Git reference `HEAD`:
Instead of typing four capital letters "HEAD", you can say "@" now, e.g. "git log @".
So for these commands
git rebase -i @~4
git log @^^..@
you can simply substitute the first occurrence of `@` with `HEAD` (or `head` if using Windows or OS X)
git rebase -i HEAD~4
git log HEAD^^..HEAD
So what does `HEAD` mean? As explained by the official Linux Kernel Git documentation for specifying Git revisions, `HEAD` is a special shortcut reference for the commit that you currently have checked-out as your working copy (or in Git terms, your "working tree"):
HEAD names the commit on which you based the changes in the working tree.
You can also read these other Stack Overflow questions on what the special reference `HEAD` means:
- HEAD and ORIG_HEAD in Git.
- What is git HEAD, exactly?.
VonC also found interesting information about why `@` was chosen as a shortcut for `head` in this Stack Overflow answer (the last section at the bottom).
Note that like it often happens with Git, while `@` is a convenient shortcut, it isn't always a valid replacement for `HEAD`. Example:
$ git bundle create temp.bundle @
Enumerating objects: 25, done.
Counting objects: 100% (25/25), done.
Compressing objects: 100% (20/20), done.
Total 25 (delta 3), reused 0 (delta 0), pack-reused 0
$ git bundle list-heads temp.bundle
c006e049da432677d1a27f0eba661671e0524710 refs/heads/master
$ git bundle create temp.bundle HEAD
Enumerating objects: 25, done.
Counting objects: 100% (25/25), done.
Compressing objects: 100% (20/20), done.
Total 25 (delta 3), reused 0 (delta 0), pack-reused 0
$ git bundle list-heads temp.bundle
c006e049da432677d1a27f0eba661671e0524710 HEAD
In this case, using `@` is more like a replacement for `master` (the branch that `HEAD` happened to be pointing to) rather than for `HEAD`. If you try to fetch from the resulting bundle later, you'll have to specify the ref you want to fetch (`master`) if you used `@`, and you won't have to to it if you specified `HEAD` explicitly.
Problem
The at-sign `@` is often used in git to specify revisions in different ways. For example, `<ref>@{<date>}` specifies the reference at its state on `<date>`. Example: `git diff master@{yesterday} master`. `<ref>@{<n>}` specific the reference at its nth prior state. Example: `git diff master@{1} master`. `@{-<n>}` specifies the nth previously checked-out branch before the current one. Example: `git checkout @{-5}`. `<ref>@{upstream}` specifies the upstream branch for the reference. Example: `git diff master@{upstream} master`. However, the `@` is being used in other ways in git commands too, like ``` git rebase -i @~4 git log @^^..@ ``` What does the at-sign `@` mean in those examples?