背景

   学习如何比较2个文件不同，便于在ORACLE分析数据块变更时用上此功能。

结论

1,diff用于比较2个文件的不同
2,diff用于比较2个文件的内容，显示结果如下 
1c1
< mynewly
---
> my
上述具体含义请见下述测试


3,  
变化标记有3种情况，各为
c  --即变化，即记录发生了变化
a  --即增加了记录
d  --即删除了记录

测试

1,创建2个相同文件
[root@seconary test_diff]# more file1.txt 
a
b
c
[root@seconary test_diff]# 
[root@seconary test_diff]# more file2.txt 
a
b
c
[root@seconary test_diff]# 


2，比较2个相同的文件
如果2个文件相同，不显示任何信息
[root@seconary test_diff]# diff file1.txt file2.txt 
[root@seconary test_diff]# 




3，比较2个文件，且右文件发生变化
修改file2.txt
[root@seconary test_diff]# more file2.txt 
anewly
b
c
[root@seconary test_diff]# 


仅1个文件变化，diff结果显示
[root@seconary test_diff]# diff file1.txt file2.txt 
1c1
< a  ---这个表示第个文件的发生变化的哪一行的开头的字母，显示形式为 < a
---
> anewly --这个表示发生变化的文件的变化后的记录


再次修改file2.txt
[root@seconary test_diff]# more file2.txt 
anewly
b
cnewly2


比较2个文件，如果发生变化文件的有多条记录，会把发生变化的多条记录也显示出来
[root@seconary test_diff]# diff file1.txt file2.txt 
1c1
< a
---
> anewly
3c3
< c
---
> cnewly2


4，比较2个文件，左文件发生变化
删除file2.txt，继续测试
[root@seconary test_diff]# rm -rf file2.txt 
[root@seconary test_diff]# 


[root@seconary test_diff]# cp file1.txt file2.txt
[root@seconary test_diff]# 


修改file1.txt
[root@seconary test_diff]# more file1.txt 
a
bnewly
c


比较2个文件
[root@seconary test_diff]# diff file1.txt file2.txt
2c2
< bnewly --发生变化的文件，修改后的内容
---
> b   --发生变化的文件，发生变化前的记行录


再次修改file1.txt
[root@seconary test_diff]# more file1.txt
asb
bnewly
c


比较2个文件
[root@seconary test_diff]# diff file1.txt file2.txt
1,2c1,2
< asb
< bnewly
---
> a
> b


删除2个比较文件，继续测试，采用单条记录多字符方式（上面测试皆采用单记录单字符）
[root@seconary test_diff]# rm file*
rm: remove regular file `file1.txt'? y
rm: remove regular file `file2.txt'? y
[root@seconary test_diff]# 




[root@seconary test_diff]# more file1.txt
my
birthday
is
[root@seconary test_diff]# more file2.txt 
my
birthday
is
[root@seconary test_diff]# 


修改左文件file1.txt
[root@seconary test_diff]# more file1.txt
mynewly
birthday
is


比较2个文件，
[root@seconary test_diff]# diff file1.txt file2.txt
1c1 --分为3个部分，1表示左文件第1行记录，c表示是改变，1表示左文件的第1条记录变成左文件第1条记录
< mynewly --分为2个部分，变化后的行内容
---  --表示左文件和右文件
> my  --分为2个部分，变化前的行内容


修改左文件
[root@seconary test_diff]# more file1.txt
mynewly
birthday
isthird


比较2个文件
[root@seconary test_diff]# diff file1.txt file2.txt
1c1
< mynewly
---
> my
3c3
< isthird
---
> is


测试下左文件新增记录,即删除deletion
[root@seconary test_diff]# more file1.txt
col1
col2
col3
[root@seconary test_diff]# 
[root@seconary test_diff]# more file2.txt
col1
col2
col3
[root@seconary test_diff]#


[root@seconary test_diff]# more file1.txt
col1
col2
col3
newaddrecord
[root@seconary test_diff]# 


[root@seconary test_diff]# diff file1.txt file2.txt
4d3
< newaddrecord
[root@seconary test_diff]# 


测试下左文件删除记录,可见变化标识为a,即增加addition
[root@seconary test_diff]# more file1.txt
col1
col3
[root@seconary test_diff]# 


[root@seconary test_diff]# diff file1.txt file2.txt
1a2
> col2
[root@seconary test_diff]# 

参考资料

http://blog.chinaunix.net/uid-26000296-id-3507646.html

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