通过实例看懂diff命令输出

摘自：http://blog.sina.com.cn/s/blog_612144f30100nkpt.html

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实例：

有这样两个文件：
程序清单1 ：hello.c
#include <stdio.h>
int main(void)
{
char msg[] = "Hello world!";
puts(msg);
printf("Welcome to use diff commond.\n");
return 0;
}
程序清单2：hello_diff.c
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
char msg[] = "Hello world,fome hello_diff.c";
puts(msg);
printf("hello_diff.c says,'Here you are,using diff.'\n");
return 0;
}
我们使用diff命令来查看这两个文件的不同之处，有一下几种方便的方法：

1、普通格式输出：

[root@localhost diff]# diff hello.c hello_diff.c
1a2
> #include <stdlib.h>
5c6
< char msg[] = "Hello world!";
---
> char msg[] = "Hello world,fome hello_diff.c";
8c9
< printf("Welcome to use diff commond.\n");
---
> printf("hello_diff.c says,'Here you are,using diff.'\n");
[root@localhost diff]#
上面的“1a2”表示后面的一个文件"hello_diff.c"比前面的一个文件"hello.c"多了一行
"5c6"表示第一个文件的第5行与第二个文件的第6行有区别

2、并排格式输出

[root@localhost diff]# diff hello.c hello_diff.c -y -W 130
#include <stdio.h> #include <stdio.h>
> #include <stdlib.h>
int main(void) int main(void)
{ {
char msg[] = "Hello world!"; | char msg[] = "Hello world,fome hello_diff.c";
puts(msg); puts(msg);
printf("Welcome to use diff commond.\n"); | printf("hello_diff.c says,'Here you are,using diff.'\
return 0; return 0;
} }
[root@localhost diff]#
这种并排格式的对比一目了然，可以快速找到不同的地方。
-W选择可以指定输出列的宽度，这里指定输出列宽为130

3、上下文输出格式

[root@localhost diff]# diff hello.c hello_diff.c -c
*** hello.c 2007-09-25 17:54:51.000000000 +0800
--- hello_diff.c 2007-09-25 17:56:00.000000000 +0800
***************
*** 1,11 ****
#include <stdio.h>
int main(void)
{
! char msg[] = "Hello world!";
puts(msg);
! printf("Welcome to use diff commond.\n");
return 0;
}
--- 1,12 ----
#include <stdio.h>
+ #include <stdlib.h>
int main(void)
{
! char msg[] = "Hello world,fome hello_diff.c";
puts(msg);
! printf("hello_diff.c says,'Here you are,using diff.'\n");
return 0;
}
[root@localhost diff]#
这种方式在开头两行作了比较文件的说明，这里有三中特殊字符：
＋比较的文件的后者比前着多一行
－比较的文件的后者比前着少一行
！比较的文件两者有差别的行

4、统一输出格式

[root@localhost diff]# diff hello.c hello_diff.c -u
--- hello.c 2007-09-25 17:54:51.000000000 +0800
+++ hello_diff.c 2007-09-25 17:56:00.000000000 +0800
@@ -1,11 +1,12 @@
#include <stdio.h>
+#include <stdlib.h>
int main(void)
{
- char msg[] = "Hello world!";
+ char msg[] = "Hello world,fome hello_diff.c";
puts(msg);
- printf("Welcome to use diff commond.\n");
+ printf("hello_diff.c says,'Here you are,using diff.'\n");
return 0;
}
[root@localhost diff]#
正如看到的那样，统一格式的输出更加紧凑，所以更易于理解，更易于修改。

5、其他

假如你想查看两个文件是否不同又不想显示差异之处的话，可以加上－q选项：
[root@localhost diff]# diff hello.c hello_diff.c -q
Files hello.c and hello_diff.c differ
[root@localhost diff]# 另外你还可以提供一些匹配规则来忽略某中差别，可以用 -I regexp
[root@localhost diff]# diff hello.c hello_diff.c -c -I include
*** hello.c 2007-09-25 17:54:51.000000000 +0800
--- hello_diff.c 2007-09-25 17:56:00.000000000 +0800
***************
*** 2,11 ****
int main(void)
{
! char msg[] = "Hello world!";
puts(msg);
! printf("Welcome to use diff commond.\n");
return 0;
}
--- 3,12 ----
int main(void)
{
! char msg[] = "Hello world,fome hello_diff.c";
puts(msg);
! printf("hello_diff.c says,'Here you are,using diff.'\n");
return 0;
}
[root@localhost diff]#
这里通过“ -I include”选项来忽略带有“ include”字样的行