正则表达式

\反斜线，转义特殊字符
$ cat data2 
The cost is $4.00 
$ sed -n ‘/\$/p‘ data2 
The cost is $4.00

锚字符
^匹配行首
$ cat data3 
This is a test line. 
this is another test line. 
A line that tests this feature. 
Yet more testing of this 
$ sed -n ‘/^this/p‘ data3 
this is another test line.
$匹配行尾
[root@localhost ~]# sed -n ‘/this$/p‘ data3.txt 
Yet more testing of this

.点号用来匹配除换行符以外的任意单个字符。
[root@localhost ~]# cat data6.sh 
The cat is sleeping. 
That is a very nice hat. 
This test is at line four. 
at ten o‘clock we‘ll go home.
匹配任何at的文本
[root@localhost ~]# sed -n ‘/.at/p‘ data6.sh 
The cat is sleeping. 
That is a very nice hat. 
This test is at line four.

[]匹配字符组，
[root@localhost ~]# sed -n ‘/[ch]at/p‘ data6.sh 
The cat is sleeping. 
That is a very nice hat. 
chat 

可以在单个表达式中用多个字符组。
$ echo "Yes" | sed -n ‘/[Yy][Ee][Ss]/p‘ 
Yes 
$ echo "yEs" | sed -n ‘/[Yy][Ee][Ss]/p‘ 
yEs 
$ echo "yeS" | sed -n ‘/[Yy][Ee][Ss]/p‘ 
yeS 
$

匹配数字
$ cat data7 
This line doesn‘t contain a number. 
This line has 1 number on it. 
This line a number 2 on it. 
This line has a number 4 on it. 
$ sed -n ‘/[0123]/p‘ data7 
This line has 1 number on it. 
This line a number 2 on it.

$ cat data8 
60633
46201 
223001 
4353 
22203
$ sed -n ‘ 
>/[0123456789][0123456789][0123456789][0123456789][0123456789]/p 
>‘ data8 
60633 
46201 
223001 
22203
成功过滤掉了不可能是邮编的那些过短的数字，因为最后一个字符组
没有字符可匹配。但它也通过了那个六位数，尽管我们只定义了5个字符组

如果要确保只匹配五位数，就必须将匹配的字符和其他字符分开，要么用空格，要么指明行首和行尾
$ sed -n ‘ 
> /^
[0123456789][0123456789][0123456789][0123456789][0123456789]$/p 
> ‘ data8 
60633 
46201 
22203

排除型字符组，匹配组中没有的字符
$ sed -n ‘/[^
ch]at/p‘ data6 
This test is at line four.

区间匹配 -只需要指定区间的第一个字符、单破折线以及区间的最后一个字符就行了。正则表达式会包括此区间内的任意字符
[root@localhost ~]# cat data8.txt 
60633
46201 
223001 
4353 
22203

[root@localhost ~]# sed -n ‘/^[0-9][0-9][0-9][0-9][0-9]$/p‘ data8.txt 
60633
22203
 如果字母出现在数据中的任何位置，这个模式都将不成立
echo "a123" | sed -n ‘/^[0-9][0-9][0-9][0-9]$/p‘

匹配字母
[root@localhost ~]# cat data6.sh 
The cat is sleeping. 
That is a very nice hat. 
This test is at line four. 
at at ten o‘clock we‘ll go home.
chat 

[c-h]at匹配了首字母在字母c和字母h之间的单词。这种情况下，只含有单词at的行将无法匹配该模式。
[root@localhost ~]# sed -n ‘/[a-ch-m]at/p‘ data6.sh 
The cat is sleeping. 
That is a very nice hat. 
chat 
该字符组允许区间a~c、h~m中的字母出现在at文本前，但不允许出现d~g的字母。


该模式不匹配fat文本，因为它没在指定的区间。
$ echo "I‘m getting too fat." | sed -n ‘/[a-ch-m]at/p‘