用了这么久linux，发现还有这么精妙的功能没有使用到，都不好意思跟人说我会linux了。

?

首先提供两个测试使用的简单文本文件

before.txt

This is a line to be deleted
This is a line that will be changed
This is a line that will be unchanged

?

?after.txt

This is a line that has been changed
This is a line that will be unchanged
This is a line that has been added

?

• diff的传统格式输出

diff before.txt after.txt 
1,2c1
< This is a line to be deleted
< This is a line that will be changed
---
> This is a line that has been changed
3a3
> This is a line that has been added

?

?说明：

1,2c1是指替换第1个文件的第1,2行到第2个文件的第2行,这里的1,2是指第1个文件的第1,2行,c是替换的意思,最后的1是第2个文件的第1行。
<号是指第1个文件更改或删除的行。
—号是分割两个文件。
>号是第2个文件中增加或删除的行。
3a3是指将第2个文件的第3行插入到第一个文件的第3行。也就是说第1个文件的:

< This is a line to be deleted
< This is a line that will be changed

?

?被替换成第2个文件的:

> This is a line that has been changed

由于第1个文件的第3行和第2个文件的第2行一致,所以不做修改。

?

由于第2个文件的第3行是第1个文件所不具有的,所以在第1个文件的最后一行增加:

> This is a line that has been added

?

• diff的统一格式输出

diff -u before.txt after.txt | tee mypatch.diff
--- before.txt  2009-06-20 05:21:49.000000000 +0800
+++ after.txt   2009-06-20 04:03:16.000000000 +0800
@@ -1,3 +1,3 @@
-This is a line to be deleted
-This is a line that will be changed
+This is a line that has been changed
 This is a line that will be unchanged
+This is a line that has been added

?

?说明：

diff -u选项是统一格式输出.
— before.txt 2009-06-20 05:21:49.000000000 +0800
— before.txt是指旧文件
+++ after.txt 2009-06-20 04:03:16.000000000 +0800
+++ after.txt是指新文件.
@@ -1,3 +1,3 @@
@@ -1,3是指第1个文件一共有3行,+1,3 @@是指第2个文件一共有3行.

-This is a line to be deleted
-This is a line that will be changed

?

?是被删除的行

+This is a line that has been changed

?

?是增加的行

This is a line that will be unchanged

?

?没有-号和+号是指该行不变,因为after.txt和before.txt都有这行.

+This is a line that has been added

?是增加的行

?

diff的统一格式比较与输出是按顺序进行的。

?

• patch命令的应用:
  

diff before.txt after.txt > mypatch.txt

?

?用patch修补before.txt文件,使before.txt和after.txt一致.

cat mypatch.txt | patch before.txt 
patching file before.txt

?

?比较两个文件，现在是一致的了

cmp before.txt after.txt

?用patch命令恢复before.txt