原生文本：

# a.txt
abcdefgh

12345678

# b.txt
abc123def
abcdefgh

0123456789

hello

使用 diff 命令：

jiaming@jiaming-VirtualBox:~/Documents$ diff a.txt b.txt 
0a1
> abc123def
3c4,6
< 12345678
---
> 0123456789
> 
> hello

diff -Naur 命令生成 patch 所需要的 .diff 文件：

jiaming@jiaming-VirtualBox:~/Documents$ diff -Naur a.txt b.txt > c.diff # 在 a.txt 基础上做了 c.diff 中的改变，变成了 b.txt
jiaming@jiaming-VirtualBox:~/Documents$ cat c.diff 
--- a.txt	2021-02-10 14:22:22.601177980 +0800
+++ b.txt	2021-02-10 14:25:44.578127476 +0800
@@ -1,3 +1,6 @@
+abc123def
 abcdefgh
 
-12345678
+0123456789
+
+hello

打补丁：

jiaming@jiaming-VirtualBox:~/Documents$ patch < c.diff # 对基础 a.txt 做 c.diff 改变，最终结果变为 b.txt **cat c.diff > patch**
patching file a.txt
jiaming@jiaming-VirtualBox:~/Documents$ cat a.txt
abc123def
abcdefgh

0123456789

hello
jiaming@jiaming-VirtualBox:~/Documents$ cat b.txt 
abc123def
abcdefgh

0123456789

hello

撤销补丁：

jiaming@jiaming-VirtualBox:~/Documents$ patch -R < c.diff 
patching file a.txt
jiaming@jiaming-VirtualBox:~/Documents$ cat a.txt
abcdefgh

12345678
jiaming@jiaming-VirtualBox:~/Documents$ cat b.txt 
abc123def
abcdefgh

0123456789

hello

---

jiaming@jiaming-VirtualBox:~/Documents$ diff b.txt a.txt 
1d0
< abc123def
4,6c3
< 0123456789
< 
< hello
---
> 12345678

jiaming@jiaming-VirtualBox:~/Documents$ diff -Naur b.txt a.txt > d.diff 
jiaming@jiaming-VirtualBox:~/Documents$ cat d.diff 
--- b.txt	2021-02-10 14:25:44.578127476 +0800
+++ a.txt	2021-02-10 14:22:22.601177980 +0800
@@ -1,6 +1,3 @@
-abc123def
 abcdefgh
 
-0123456789
-
-hello
+12345678