一、使用正则表达式匹配行首行尾，需要注意空格与
1.vi文本在每行的末尾都会有影藏字符$，表示本行的结束，那么在一行的结束加上空格或者换行符，那 么隐藏字符$也会跟在空格或者换行符之后，那么如果不注意这个在搜索时就会出错。
如：
[root@c1 ~]# cat -An regular_express.txt
1 ource" is a good mechanism to develop programs.$
2 apple is my favorite food. $
3 Football game is not use feet only. $
4 this dress doesn't fit me.$
5 However, this dress is about $ 3183 dollars.^M$
6 GNU is free air not free beer.^M$
7 Her hair is very beauty.^M$
8 I can't finish the test.^M$
9 Oh! The soup taste good.^M$
10 motorcycle is cheap than car.$
11 This window is clear.$
这是如果想要使用grep 搜索以.结尾的字符，不注意空格或者换行符，其结果：
[root@c1 ~]# cat -n regular_express.txt | grep '\.$'
1 ource" is a good mechanism to develop programs.
4 this dress doesn't fit me.
10 motorcycle is cheap than car.
11 This window is clear.
那么符合标准的2、3行则会搜索不出来。
2. 以多个空格开头，后面接着字符，在使用^搜索时也会有这样的问题：
[root@c1 ~]# grep -n '^[a-z]' regular_express.txt
4:this dress doesn't fit me.
10:motorcycle is cheap than car.
没有搜索出1、2行
补充：
使用 cat -n regular_express.txt | grep '^[a-z]' 没有输出正确的结果，很奇怪
管道符使用需谨慎！
二、正则表达式中，以搜索匹配的字符作为目的，感觉还少则【逻辑非】，用来缩小匹配范围。
在设计grep工具时，作者应该是考虑到，尽量匹配到所有有用的信息，不丢失信息，缩小范围可以放在下一步。
三、使用grep参数之间的影响
[root@c1 ~]# grep -in '^$' regular_express.txt
2:4:6:8:10:12:14:16:18:20:22:24:26:28:30:32:34:36:38:40:42:43:
[root@c1 ~]# grep -n '^$' regular_express.txt
22:
在使用grep搜索空格时，加大小写忽略会影响到输出结果，原因未知。
四、使用管道命令时，前面命令参数会影响到后面的结果：
[root@c1 ~]# cat -n regular_express.txt | grep -v '^$' | grep -v '^#'
1 ource" is a good mechanism to develop programs.
2 apple is my favorite food.
3 Football game is not use feet only.
4 this dress doesn't fit me.
5 However, this dress is about $ 3183 dollars.^M
6 GNU is free air not free beer.^M
7 Her hair is very beauty.^M
8 I can't finish the test.^M
9 Oh! The soup taste good.^M
10 motorcycle is cheap than car.
11 This window is clear.
12 the symbol '*' is represented as start.
13 Oh! My god!
14 The gd software is a library for drafting programs.^M
15 You are the best is mean you are the no. 1.
16 The world <Happy> is the same with "glad".
17 I like dog.
18 google is the best tools for search keyword.
19 goooooogle yes!
20 go! go! Let's go.
21 # I am VBird
22
错误结果
[root@c1 ~]# cat regular_express.txt | grep -v '^$' | grep -v '^#'
ource" is a good mechanism to develop programs.
apple is my favorite food.
Football game is not use feet only.
this dress doesn't fit me.
However, this dress is about $ 3183 dollars.^M
GNU is free air not free beer.^M
Her hair is very beauty.^M
I can't finish the test.^M
Oh! The soup taste good.^M
motorcycle is cheap than car.
This window is clear.
the symbol '*' is represented as start.
Oh! My god!
The gd software is a library for drafting programs.^M
You are the best is mean you are the no. 1.
The world <Happy> is the same with "glad".
I like dog.
google is the best tools for search keyword.
goooooogle yes!
go! go! Let's go.
正确结果