Git - Rebase命令介绍

Git rebase 是版本控制系统 Git 中一个功能强大、使用广泛的命令。它用于将一个分支中的改动整合到另一个分支中。rebase与merge不同， merge会创建一个新的提交，而rebase则是将一系列提交移动或合并到一个新的基础提交中。下面是详细解释：

Git Rebase 的作用是什么？

rebase的本质是将当前分支的提交重新应用到另一个基础提交上。这通常用于保持线性的项目历史，避免产生不必要的合并提交。

Git 重定向的工作原理

请看下面的例子，feature分支基于main分支的一个较早提交：

A---B---C---D  main\E---F---G  feature

如果您在feature分支上运行 git rebase main，Git 会：

1. 识别分支的共同祖先（本例中为 B）。
2. 确定自共同祖先（E、F 和 G）以来，feature 中每次提交所引入的差异。
3. 从 feature 分支中暂时删除这些提交。
4. 将 main 分支中的提交应用到当前提交 (A-B-C-D)。
5. 将 E、F 和 G 提交引入的改动重新应用到 D 分支之上。

重定向后，历史记录将如下所示：

A---B---C---D  main\E'---F'---G'  feature

注意 E、F 和 G 已经被新的提交版本 E'、F' 和 G' 取代。这些新提交的改动相同，但提交哈希值不同，因为它们现在基于 D。

重置基准命令

• 交互式重置： git rebase -i <base-branch>。

  • 允许编辑、重新排序、压制或删除提交。

• 常规重置： git rebase <base-branch>

  • 简单地将当前分支的提交重新应用到指定的基本分支上。

Git 重置基准的好处

• 更简洁的历史： 线性历史，没有不必要的合并提交。
• 更易于阅读： 更容易跟踪项目历史。
• 解决冲突： 通常在重置过程中更容易逐步解决冲突，而不是在合并过程中一次性解决所有冲突。

Git 重置的注意事项

• 重写历史： 重置会改变提交哈希值，这意味着会改写历史。如果你已经与他人共享了提交，这可能会造成问题。
• 协调： 如果在一个团队中工作，应仔细协调重置基准工作，以避免冲突和重复工作。

何时使用重置与合并

• 重置：

  • 在推送到共享版本库之前，用于本地分支维护。
  • 用于保持干净、线性的项目历史。

• 合并：

  • 用于保留分支分叉和合并的完整历史。
  • 在将特性分支整合到主线分支时使用，以记录实际的分支结构。

###工作流程示例

1. 更新特性分支：

   git checkout featuregit rebase main

2. 解决冲突：
   如果存在冲突，Git 会暂停并允许您解决它们。解决后，使用

   git add <filegit rebase --continue

或终止

   git rebase --abort

3. 推送更改（rebase 后通常需要强制推送）：

   git push origin feature --force

总之，"git rebase "是简化和清理提交历史的工具，但在使用时应了解它对项目提交历史的影响以及团队内部的协调。

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Git rebase is a powerful and widely used command in Git, a version control system. It is used to integrate changes from one branch into another. Unlike merging, which creates a new commit for the merge, rebasing moves or combines a sequence of commits to a new base commit. Here’s a detailed explanation:

What Does Git Rebase Do?

Rebasing essentially re-applies commits from your current branch onto another base commit. This is often used to maintain a linear project history, avoiding the creation of unnecessary merge commits.

How Git Rebase Works

Consider the following example where feature branch is based on an older commit of the main branch:

A---B---C---D  main\E---F---G  feature

If you run git rebase main while on the feature branch, Git will:

1. Identify the common ancestor of the branches (B in this case).
2. Determine the difference introduced by each commit in feature since the common ancestor (E, F, and G).
3. Temporarily remove these commits from the feature branch.
4. Apply the commits from main branch up to the current commit (A-B-C-D).
5. Reapply the changes introduced by the commits E, F, and G on top of D.

After rebasing, the history would look like this:

A---B---C---D  main\E'---F'---G'  feature

Notice that E, F, and G have been replaced with new commits E', F', and G'. These new commits have the same changes but different commit hashes because they are now based on D.

Commands for Rebasing

• Interactive Rebase: git rebase -i <base-branch>

  • Allows you to edit, reorder, squash, or drop commits.

• Regular Rebase: git rebase <base-branch>

  • Simply re-applies commits from the current branch onto the specified base branch.

Benefits of Git Rebase

• Cleaner History: Linear history without unnecessary merge commits.
• Easier to Read: Makes it easier to follow the project history.
• Conflict Resolution: Often easier to resolve conflicts incrementally during a rebase rather than all at once during a merge.

Caveats of Git Rebase

• Rewriting History: Rebasing changes commit hashes, which means it rewrites history. This can be problematic if you have already shared the commits with others.
• Coordination: If working in a team, coordinate rebases carefully to avoid conflicts and duplicated work.

When to Use Rebase vs Merge

• Rebase:

  • Use for local branch maintenance before pushing to a shared repository.
  • Use to keep a clean and linear project history.

• Merge:

  • Use when you want to preserve the complete history of how branches have diverged and merged.
  • Use when integrating feature branches into mainline branches in a way that records the actual branching structure.

Example Workflow

1. Update Feature Branch:

   git checkout featuregit rebase main

2. Resolve Conflicts:
   If there are conflicts, Git will pause and allow you to resolve them. After resolving, use:

   git add <file>git rebase --continue

or to abort:

   git rebase --abort

3. Push Changes (force push is often required after rebase):

   git push origin feature --force

In summary, git rebase is a tool for streamlining and cleaning up your commit history, but it should be used with an understanding of its effects on your project’s commit history and coordination within your team.