Git 简明教程

Git - Fix Mistakes

人非圣贤，孰能无过。因此，每个 VCS 都提供了在一定范围内修复错误的功能。Git 提供了一个功能，我们可以使用该功能撤销对本地存储库所做的修改。

To err is human. So every VCS provides a feature to fix mistakes until a certain point. Git provides a feature that we can use to undo the modifications that have been made to the local repository.

假设用户错误地对他的本地存储库进行了一些更改，然后想要撤销这些更改。在这种情况下， revert 操作将发挥重要作用。

Suppose the user accidentally does some changes to his local repository and then wants to undo these changes. In such cases, the revert operation plays an important role.

Revert Uncommitted Changes

让我们假设 Jerry 错误地修改了他本地存储库中的一个文件。但是，他想要撤销他的修改。为了处理这种情况，我们可以使用 git checkout 命令。我们可以使用这个命令来还原文件的内容。

Let us suppose Jerry accidentally modifies a file from his local repository. But he wants to undo his modification. To handle this situation, we can use the git checkout command. We can use this command to revert the contents of a file.

[jerry@CentOS src]$ pwd
/home/jerry/jerry_repo/project/src

[jerry@CentOS src]$ git status -s
M string_operations.c

[jerry@CentOS src]$ git checkout string_operations.c

[jerry@CentOS src]$ git status –s

此外，我们可以使用 git checkout 命令从本地存储库中获取已删除的文件。让我们假设 Tom 从本地存储库中删除了一个文件，并且我们想要恢复这个文件。我们可以使用相同的命令来实现这一点。

Further, we can use the git checkout command to obtain a deleted file from the local repository. Let us suppose Tom deletes a file from the local repository and we want this file back. We can achieve this by using the same command.

[tom@CentOS src]$ pwd
/home/tom/top_repo/project/src

[tom@CentOS src]$ ls -1
Makefile
string_operations.c

[tom@CentOS src]$ rm string_operations.c

[tom@CentOS src]$ ls -1
Makefile

[tom@CentOS src]$ git status -s
D string_operations.c

Git 在文件名之前显示了字母 D 。这表示该文件已从本地存储库中删除。

Git is showing the letter D before the filename. This indicates that the file has been deleted from the local repository.

[tom@CentOS src]$ git checkout string_operations.c

[tom@CentOS src]$ ls -1
Makefile
string_operations.c

[tom@CentOS src]$ git status -s

Note − 我们可以在提交前执行所有这些操作。

Note − We can perform all these operations before commit.

Remove Changes from Staging Area

我们已经看到当我们执行一个添加操作时，文件从本地仓库移动到暂存区域。如果一个用户意外地修改了一个文件并将其添加到暂存区域中，他可以使用 git checkout 命令撤销他的修改。

We have seen that when we perform an add operation, the files move from the local repository to the stating area. If a user accidently modifies a file and adds it into the staging area, he can revert his changes, by using the git checkout command.

在 Git 中，有一个 HEAD 指针始终指向最新的提交。如果你想要撤销一个来自暂存区域的修改，你可以使用 git checkout 命令，使用 checkout 命令的时候，你必须提供一个额外的参数，即 HEAD 指针。额外的提交指针参数指示 git checkout 命令重置工作树并移除暂存修改。

In Git, there is one HEAD pointer that always points to the latest commit. If you want to undo a change from the staged area, then you can use the git checkout command, but with the checkout command, you have to provide an additional parameter, i.e., the HEAD pointer. The additional commit pointer parameter instructs the git checkout command to reset the working tree and also to remove the staged changes.

假设 Tom 从他的本地仓库中修改了一个文件。如果我们查看这个文件的状态，它将会显示文件已经修改但是尚未添加到暂存区域中。

Let us suppose Tom modifies a file from his local repository. If we view the status of this file, it will show that the file was modified but not added into the staging area.

tom@CentOS src]$ pwd
/home/tom/top_repo/project/src
# Unmodified file

[tom@CentOS src]$ git status -s

# Modify file and view it’s status.
[tom@CentOS src]$ git status -s
M string_operations.c

[tom@CentOS src]$ git add string_operations.c

Git status 显示文件出现在暂存区域中，现在使用 git checkout 命令撤销它并查看撤销的文件的状态。

Git status shows that the file is present in the staging area, now revert it by using the git checkout command and view the status of the reverted file.

[tom@CentOS src]$ git checkout HEAD -- string_operations.c

[tom@CentOS src]$ git status -s

Move HEAD Pointer with Git Reset

完成了一些修改之后，你可能决定移除这些修改。Git reset 命令用于重置或撤销修改。我们可以执行三种不同类型的重置操作。

After doing few changes, you may decide to remove these changes. The Git reset command is used to reset or revert changes. We can perform three different types of reset operations.

下图展示了 Git reset 命令的图片表示。

Below diagram shows the pictorial representation of Git reset command.

before git reset
after git reset

Soft

每个分支都有一个 HEAD 指针，指向最新的提交。如果我们使用带有 --soft 选项的 Git reset 命令，后面跟着提交 ID，那么它仅仅会在不销毁任何东西的情况下重置 HEAD 指针。

Each branch has a HEAD pointer, which points to the latest commit. If we use Git reset command with --soft option followed by commit ID, then it will reset the HEAD pointer only without destroying anything.

.git/refs/heads/master 文件储存了 HEAD 指针的提交 ID。我们可以使用 git log -1 命令验证它。

.git/refs/heads/master file stores the commit ID of the HEAD pointer. We can verify it by using the git log -1 command.

[jerry@CentOS project]$ cat .git/refs/heads/master
577647211ed44fe2ae479427a0668a4f12ed71a1

现在，查看最新的提交 ID，它将会与上面的提交 ID 相匹配。

Now, view the latest commit ID, which will match with the above commit ID.

[jerry@CentOS project]$ git log -2

上述命令将产生以下结果。

The above command will produce the following result.

commit 577647211ed44fe2ae479427a0668a4f12ed71a1
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 10:21:20 2013 +0530

Removed executable binary


commit 29af9d45947dc044e33d69b9141d8d2dad37cc62
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 10:16:25 2013 +0530

Added compiled binary

让我们重置 HEAD 指针。

Let us reset the HEAD pointer.

[jerry@CentOS project]$ git reset --soft HEAD~

现在，我们简单地将 HEAD 指针回退一个位置。让我们检查 .git/refs/heads/master file 的内容。

Now, we just reset the HEAD pointer back by one position. Let us check the contents of .git/refs/heads/master file.

[jerry@CentOS project]$ cat .git/refs/heads/master
29af9d45947dc044e33d69b9141d8d2dad37cc62

文件中的提交 ID 已经改变，现在通过查看提交信息来验证它。

Commit ID from file is changed, now verify it by viewing commit messages.

jerry@CentOS project]$ git log -2

上述命令将产生以下结果。

The above command will produce the following result.

commit 29af9d45947dc044e33d69b9141d8d2dad37cc62
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 10:16:25 2013 +0530

Added compiled binary


commit 94f7b26005f856f1a1b733ad438e97a0cd509c1a
Author: Jerry Mouse <jerry@tutorialspoint.com>
Date: Wed Sep 11 10:08:01 2013 +0530

Added Makefile and renamed strings.c to string_operations.c

mixed

Git reset 带有 --mixed 选项会撤销那些尚未提交的来自暂存区域的修改。它仅仅会撤销来自暂存区域的修改。对文件工作副本所做的实际修改不会受到影响。默认的 Git reset 等同于 git reset — mixed。

Git reset with --mixed option reverts those changes from the staging area that have not been committed yet. It reverts the changes from the staging area only. The actual changes made to the working copy of the file are unaffected. The default Git reset is equivalent to the git reset — mixed.

hard

如果你对 Git reset 命令使用 --hard 选项，它将会清空暂存区域；它将会将 HEAD 指针重置为特定提交 ID 的最新提交，也会删除本地文件修改。

If you use --hard option with the Git reset command, it will clear the staging area; it will reset the HEAD pointer to the latest commit of the specific commit ID and delete the local file changes too.

让我们检查提交 ID。

Let us check the commit ID.

[jerry@CentOS src]$ pwd
/home/jerry/jerry_repo/project/src

[jerry@CentOS src]$ git log -1

上述命令将产生以下结果。

The above command will produce the following result.

commit 577647211ed44fe2ae479427a0668a4f12ed71a1
Author: Tom Cat <tom@tutorialspoint.com>
Date: Wed Sep 11 10:21:20 2013 +0530

Removed executable binary

Jerry 通过在文件开头添加单行注释来修改了文件。

Jerry modified a file by adding single-line comment at the start of file.

[jerry@CentOS src]$ head -2 string_operations.c
/* This line be removed by git reset operation */
#include <stdio.h>

他使用 git status 命令验证了它。

He verified it by using the git status command.

[jerry@CentOS src]$ git status -s
M string_operations.c

Jerry 将修改的文件添加到暂存区域，并使用 git status 命令验证了它。

Jerry adds the modified file to the staging area and verifies it with the git status command.

[jerry@CentOS src]$ git add string_operations.c
[jerry@CentOS src]$ git status

上述命令将产生以下结果。

The above command will produce the following result.

# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
#
#
modified: string_operations.c
#

Git 状态显示文件出现在暂存区域中。现在，使用重置命令——硬选项重置 HEAD。

Git status is showing that the file is present in the staging area. Now, reset HEAD with — hard option.

[jerry@CentOS src]$ git reset --hard 577647211ed44fe2ae479427a0668a4f12ed71a1

HEAD is now at 5776472 Removed executable binary

Git 重置命令成功，它将从暂存区撤消文件并删除对该文件进行的所有本地更改。

Git reset command succeeded, which will revert the file from the staging area as well as remove any local changes made to the file.

[jerry@CentOS src]$ git status -s

Git 状态显示文件已从暂存区域撤消。

Git status is showing that the file has been reverted from the staging area.

[jerry@CentOS src]$ head -2 string_operations.c
#include <stdio.h>

head 命令还显示了重置操作也移除了本地更改。

The head command also shows that the reset operation removed the local changes too.