git diff 命令
简介
git diff 是 Git 中一个非常重要的命令，用于显示文件之间的差异。它可以比较工作区、暂存区、不同提交之间的差异，帮助开发者了解代码的变化。
基本概念
Git 中有三个主要区域：
- 工作区（Working Directory）：当前正在编辑的文件
- 暂存区（Staging Area / Index）：已使用
git add 添加的文件
- 仓库（Repository）：已提交的版本
git diff 可以比较这些区域之间的差异。
命令语法
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| git diff [选项] [--] [<路径名>...]
git diff [选项] --cached [<提交>] [--] [<路径名>...]
git diff [选项] <提交> [--] [<路径名>...]
git diff [选项] <提交1> <提交2> [--] [<路径名>...]
git diff [选项] <提交1>..<提交2> [--] [<路径名>...]
git diff [选项] <提交1>...<提交2> [--] [<路径名>...]
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查看帮助文档
常用选项
| 选项 |
说明 |
--cached, --staged |
比较暂存区和最后一次提交 |
-p, -u, --unified=<n> |
显示统一格式的差异，n 为上下文行数 |
--stat |
显示统计信息（修改的文件和行数） |
--name-only |
只显示文件名 |
--name-status |
显示文件名和状态（M/A/D/R） |
-w, --ignore-all-space |
忽略所有空白字符的差异 |
-b, --ignore-space-change |
忽略空白字符数量的变化 |
--ignore-blank-lines |
忽略空白行的差异 |
-S<string> |
显示包含指定字符串的更改 |
-G<regex> |
显示匹配正则表达式的更改 |
--color[=<when>] |
使用颜色高亮显示差异 |
--no-color |
不使用颜色 |
-R |
反向显示差异（新文件在前） |
--word-diff |
按单词显示差异 |
--word-diff-regex=<regex> |
使用正则表达式定义单词边界 |
--ignore-submodules |
忽略子模块的更改 |
--submodule=<format> |
指定子模块差异的格式 |
--ext-diff |
允许执行外部 diff 工具 |
--no-ext-diff |
禁止执行外部 diff 工具 |
--no-index |
比较两个路径，即使它们不在 Git 仓库中 |
基本使用
1. 比较工作区和暂存区
显示工作区中已修改但未暂存的文件差异（默认行为）。
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$ git diff
$ git diff README.md
$ git diff src/
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示例输出：
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@@ -10,7 +10,7 @@ int main() {
printf("Hello, World!\n");
- printf("Old message\n");
+ printf("New message\n");
return 0;
}
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2. 比较暂存区和最后一次提交
使用 --cached 或 --staged 选项。
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$ git diff --cached
$ git diff --staged
$ git diff --cached README.md
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3. 比较工作区和最后一次提交
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$ git diff HEAD
$ git diff HEAD README.md
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4. 比较两次提交
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$ git diff commit1 commit2
$ git diff abc1234 def5678
$ git diff HEAD~1 HEAD
$ git diff commit1..commit2
$ git diff commit1...commit2
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5. 比较分支
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$ git diff branch1 branch2
$ git diff main develop
$ git diff main origin/main
$ git diff main..develop
$ git diff main...develop
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6. 比较提交和文件
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$ git diff HEAD src/main.c
$ git diff commit1 commit2 -- README.md
$ git diff --cached HEAD~1
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输出格式说明
Git 默认使用统一格式显示差异：
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@@ -1,3 +1,3 @@
line 1
-line 2 (old)
+line 2 (new)
line 3
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格式说明：
--- a/file.txt：原始文件+++ b/file.txt：修改后的文件@@ -1,3 +1,3 @@：块头，表示从第1行开始，共3行-：删除的行+：添加的行- 没有符号：未修改的行
上下文行数
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$ git diff
$ git diff -U5
$ git diff --unified=10
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常用选项详解
–stat：显示统计信息
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$ git diff --stat
README.md | 2 +-
src/main.c | 5 +++--
2 files changed, 4 insertions(+), 3 deletions(-)
$ git diff --stat --summary
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–name-only：只显示文件名
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$ git diff --name-only
README.md
src/main.c
src/utils.h
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–name-status：显示文件名和状态
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$ git diff --name-status
M README.md
M src/main.c
A src/utils.h
D oldfile.txt
R100 oldname.txt newname.txt
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状态码说明：
M：修改（Modified）A：添加（Added）D：删除（Deleted）R：重命名（Renamed）C：复制（Copied）
忽略空白字符
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$ git diff -w
$ git diff -b
$ git diff --ignore-blank-lines
$ git diff -w -b --ignore-blank-lines
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颜色输出
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$ git diff --color
$ git diff --no-color
$ git diff --color=always
$ git diff --color=auto
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搜索特定更改
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$ git diff -S"function_name"
$ git diff -G"^import"
$ git diff -S"TODO" --stat
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单词级别差异
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$ git diff --word-diff
$ git diff --word-diff-regex='[A-Za-z0-9]+'
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示例输出：
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@@ -1 +1 @@
This is [-old-]{+new+} text.
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高级用法
比较特定路径
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$ git diff HEAD -- README.md
$ git diff HEAD -- src/
$ git diff HEAD -- file1.txt file2.txt
$ git diff HEAD -- "*.py"
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限制上下文行数
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$ git diff -U0
$ git diff -U1
$ git diff -U20
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反向显示
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$ git diff -R
$ git diff -R commit1 commit2
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比较非 Git 文件
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$ git diff --no-index file1.txt file2.txt
$ git diff --no-index dir1/ dir2/
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使用外部 diff 工具
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$ git config --global diff.tool vimdiff
$ git difftool
$ git difftool --tool=vimdiff
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实际应用场景
场景1：查看未暂存的更改
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$ git diff
$ git diff src/main.c
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场景2：查看已暂存的更改
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$ git diff --cached
$ git diff --cached README.md
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场景3：查看所有更改（工作区 + 暂存区）
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$ git diff HEAD
$ git diff
$ git diff --cached
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场景4：代码审查
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$ git diff main..feature-branch
$ git diff --stat main..feature-branch
$ git diff main..feature-branch -- src/main.c
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场景5：查看提交历史中的更改
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$ git diff HEAD~1 HEAD
$ git diff HEAD~3 HEAD
$ git diff abc1234^..abc1234
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场景6：查找特定更改
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$ git diff -S"TODO"
$ git diff -G"function.*\(\)"
$ git diff commit1..commit2 -S"bug"
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场景7：忽略空白字符差异
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$ git diff -w
$ git diff -b --ignore-blank-lines
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场景8：生成补丁文件
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$ git diff > changes.patch
$ git diff commit1 commit2 > feature.patch
$ git apply changes.patch
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场景9：比较远程分支
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$ git diff main origin/main
$ git fetch origin
$ git diff main origin/main
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场景10：查看文件重命名
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$ git diff --name-status HEAD~1 HEAD
$ git diff -M HEAD~1 HEAD
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与其他命令的组合
git diff + git log
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$ git log --oneline
$ git diff commit1 commit2
$ git log -p
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git diff + git show
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$ git show commit1
$ git diff commit1^..commit1
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git diff + git stash
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$ git stash show -p
$ git diff stash@{0}
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git diff + grep
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$ git diff | grep "function_name"
$ git diff -G"pattern" | grep "file"
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常见问题和技巧
问题1：diff 输出太长
解决方案：
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$ git diff --name-only
$ git diff --stat
$ git diff -U3
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问题2：只想看特定类型的更改
解决方案：
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$ git diff --diff-filter=A
$ git diff --diff-filter=D
$ git diff --diff-filter=M
$ git diff --diff-filter=AM
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问题3：忽略某些文件的差异
解决方案：
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$ git diff -- ':!*.log' ':!*.tmp'
$ git diff -- ':!.gitignore'
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问题4：查看二进制文件的差异
解决方案：
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$ git config diff.pdf.textconv pdftotext
$ git difftool binary-file.pdf
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问题5：比较时包含未跟踪的文件
解决方案：
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$ git status
$ git add untracked-file.txt
$ git diff --cached
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技巧1：使用别名简化命令
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$ git config --global alias.d 'diff'
$ git config --global alias.dc 'diff --cached'
$ git config --global alias.ds 'diff --stat'
$ git d
$ git dc
$ git ds
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技巧2：使用颜色主题
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$ git config --global color.diff auto
$ git config --global color.diff.meta "yellow bold"
$ git config --global color.diff.frag "magenta bold"
$ git config --global color.diff.old "red bold"
$ git config --global color.diff.new "green bold"
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技巧3：保存差异到文件
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$ git diff > diff.txt
$ git diff commit1 commit2 > feature-diff.txt
$ git diff >> all-diffs.txt
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技巧4：在编辑器中使用
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$ git diff | vim -
$ git diff | less
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最佳实践
1. 提交前检查
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$ git diff --cached
$ git diff HEAD
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2. 代码审查
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$ git diff main..feature-branch --stat
$ git diff main..feature-branch
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3. 调试问题
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$ git diff commit1..commit2
$ git diff -S"bug" commit1..commit2
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4. 文档化更改
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$ git diff > CHANGES.patch
$ git diff --stat > CHANGES.txt
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5. 使用合适的上下文
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$ git diff -U10
$ git diff -U3
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6. 忽略无关差异
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$ git diff -w
$ git diff -b --ignore-blank-lines
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输出格式说明
格式：@@ -起始行,行数 +起始行,行数 @@
-10,7：原始文件从第10行开始，共7行+10,7：新文件从第10行开始，共7行
行标记
（空格）：未修改的行-：删除的行（红色）+：添加的行（绿色）\：行尾没有换行符
文件头
--git：Git 格式a/file.txt：原始文件路径b/file.txt：新文件路径index：文件的 blob 对象哈希100644：文件模式（普通文件）
总结
git diff 是 Git 中最重要的命令之一，掌握它可以帮助你：
- 查看更改：了解工作区、暂存区和提交之间的差异
- 代码审查：比较分支和提交，进行代码审查
- 调试问题：查找引入问题的更改
- 生成补丁：创建补丁文件用于分享或备份
- 统计分析：查看代码更改的统计信息
通过合理使用 git diff 的各种选项，可以更高效地查看和理解代码的变化。
