Linux之正则表达式1

正则表达式是对字符串操作的一种逻辑公式，就是用事先定义好的一些特定字符、及这些特定字符的组合，组成一个“规则字符串”，这个“规则字符串”用来表达对字符串的一种过滤逻辑。适当使用正则表达式可以提高工作效率。正则表达式帮助文档链接: https://pan.baidu.com/s/1Sws9HBQSR4XSJQZ1dm9G0w 密码: 178u

我们使用的regular_express.txt如下所示

"Open Source" 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 $  dollars.
GNU is free air not free beer.
Her hair is very beauty.
I can't finish the test.
Oh! The soup taste good.
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.
You are the best is mean you are the no. .
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.
# I am VBird

用cat -An regular_express.txt如下(至于为什么有^M$请转至windows与linux换行规则)：

vbird@Ubuntu1604:~$ cat -An regular_express.txt.bak
       "Open Source" 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 $  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!^IMy god!$
      The gd software is a library for drafting programs.^M$
      You are the best is mean you are the no. .$
      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.$
      # I am VBird$
      $

基础正则表示法

普通字符：字母、数字、汉字、下划线、以及后边章节中没有特殊定义的标点符号，都是"普通字符"。表达式中的普通字符，在匹配一个字符串的时候，匹配与之相同的一个字符。见例1

简单的转义字符：一些不便书写的字符，采用在前面加 "\" 的方法。还有其他一些在后边章节中有特殊用处的标点符号，在前面加 "\" 后，就代表该符号本身。比如：^, $ 都有特殊意义，如果要想匹配字符串中 "^" 和 "$" 字符，则表达式就需要写成 "\^" 和 "\$"。

表达式	可匹配	表达式	可匹配
\r，\n	回车或换行符	\^	可匹配^本身
\t	制表符	\$	可匹配$本身
\\	代表\本身	\.	可匹配.本身
\d	匹配1个数字字符，等于[0-9]	\D	匹配1个非数字字符，等于[^0-9]
\w	匹配包括下划线的任何单词字符。等价于“[A-Za-z0-9_]”	\W	匹配任何非单词字符和下划线。等价于“[^A-Za-z0-9_]”

自定义能够匹配"多种字符"的表达式： 使用方括号 [ ] 包含一系列字符，能够匹配其中任意一个字符。用 [^ ] 包含一系列字符，则能够匹配其中字符之外的任意一个字符。同样的道理，虽然可以匹配其中任意一个，但是只能是一个，不是多个。见例2、例3、例4、例5

表达式	可匹配
[abcd]	可匹配adcd中的任何1个，有且只有1个
[^abc]	可匹配不是abc的任意字符
[f-k]	可匹配"f"~"k"中任意字符
[^A-F0-5]	可匹配"A"~"F"、"0"~"5"之外的任何字符
x|y	匹配x或y。例如，“z|food”能匹配“z”或“food”。“(z|f)ood”则匹配“zood”或“food”

代表抽象意义的特殊符号：见例6.

表达式	作用
^	行首，不匹配任何字符（例6、例7）
$	行尾，不匹配任何字符（例7）
.	小数点可以匹配除了换行符（\n）以外的任意一个字符，有且只有一个（例8）
*	重复前一个字符 0 到无穷多次（例9）

修饰匹配次数的特殊符号：

表达式	作用
{n}	表达式重复n次，"A\{2\}"，相当于"AA"（例10）
{m,n}	表达式重复m~n次，"AB\{2,4\}"，相当于"ABB"、"ABBB"、"ABBBB"（例12）
{n,}	表达式至少重复n次，"AB\{2,\}"，相当于"ABB"、"ABBB".....（例11）
+	重复1个或1个以上的前一个RE字符，"go+d",相当于"god"、"good"、"goood"。等于"go{1,}d"
?	重复0个或1个前一个RE字符，"g?d"，相当于"gd"、"god"。等于"go{0,1}d"

例1.

vbird@Ubuntu1604:~$ grep -n "the" regular_express.txt
:I can't finish the test.
:the symbol '*' is represented as start.
:You are the best is mean you are the no. .
:The world <Happy> is the same with "glad".
:google is the best tools for search keyword.

例2.

vbird@Ubuntu1604:~$ grep -n "t[ae]st" regular_express.txt
:I can't finish the test.
:Oh! The soup taste good.

例3.

vbird@Ubuntu1604:~$ grep -n "[^g]oo" regular_express.txt
:apple is my favorite food.
:Football game is not use feet only.
:google is the best tools for search keyword.   //google不属于匹配到，但是可以匹配到tools，grep是以行为处理单位.
:goooooogle yes!    //goooooogle中有多oo，oo前面有o，所以是可以匹配上的

例4.

vbird@Ubuntu1604:~$ grep -n "[^a-z]oo" regular_express.txt  //查找"oo"前不是小写字符的字符串.
:Football game is not use feet only.

例5.

vbird@Ubuntu1604:~$ grep -n "[0-9]" regular_express.txt
:However, this dress is about $  dollars.
:You are the best is mean you are the no. .

例6.

vbird@Ubuntu1604:~$ grep -n "^[^a-zA-Z0-9]" regular_express.txt   //[]外的^代表行首意思，[]内的^代表反向选择，这个表达式意思是查找行首既不是字母也不是数字的字符串
:"Open Source" is a good mechanism to develop programs.
:# I am VBird

例7.

vbird@Ubuntu1604:~$ grep -n "^$" regular_express.txt   //找出空白行
:

例8.

vbird@Ubuntu1604:~$ grep -n "g..d" regular_express.txt
:"Open Source" is a good mechanism to develop programs.
:Oh! The soup taste good.
:The world <Happy> is the same with "glad".

例9.

vbird@Ubuntu1604:~$ grep -n "ooo*" regular_express.txt
:"Open Source" is a good mechanism to develop programs.
:apple is my favorite food.
:Football game is not use feet only.
:Oh! The soup taste good.
:google is the best tools for search keyword.
:goooooogle yes!

例10.

vbird@Ubuntu1604:~$ grep -n "go\{2\}d" regular_express.txt
:"Open Source" is a good mechanism to develop programs.
:Oh! The soup taste good.

例11.

vbird@Ubuntu1604:~$ grep -n "go\{2,\}" regular_express.txt
:"Open Source" is a good mechanism to develop programs.
:Oh! The soup taste good.
:google is the best tools for search keyword.
:goooooogle yes!

例12.

vbird@Ubuntu1604:~$ grep -n "go\{2,3\}g" regular_express.txt
:google is the best tools for search keyword.

综合例子.在文件/etc/manpath.config中，去除空白行和以#开头行，然后查找还有"opt"字符串的数据.

vbird@Ubuntu1604:~$ grep -v "^$" /etc/manpath.config | grep -v "^#" | grep "opt"
MANPATH_MAP     /opt/bin                /opt/man
MANPATH_MAP     /opt/sbin               /opt/man
MANDB_MAP       /opt/man                /var/cache/man/opt