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linux grep高级用法

1. 使用用正则表达式

语法:
grep "REGEX" filename


如果你能有效地利用正则表达式,这是个很有用的特点。在下面的例子中,搜索全部以“lines”开始以“empty”结束的字串,如搜索“lines[之间任意字]empty” ,并且忽略大小写。

 

$ grep -i "lines.*empty" demo_file
Two lines above this line is empty.

 

正则表达式遵循的几个重复的操作

  • ? 最多匹配一次
  • * 匹配零次或者任意多次
  • + 匹配一次以上
  • {n} 匹配n次
  • {n,} 最少匹配n次
  • {,m} 最多匹配m次
  • {n,m} 匹配n到m次

2. 用grep -w搜索整个词,而不是词中的部分字串

使用-w选项搜索一个单词,并且避免搜索到词中的部分字串。

下例搜索"is"。如果不加-w选项,将显示“is”, “his”, “this” 等所有包含“is”的行。

$ grep -i "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
This Line Has All Its First Character Of The Word With Upper Case.
Two lines above this line is empty.
And this is the last line.


下例使用了-w选项,请注意结果中不包含 “This Line Has All Its First Character Of The Word With Upper Case”, 虽然 “This”中包含“is”。

$ grep -iw "is" demo_file
THIS LINE IS THE 1ST UPPER CASE LINE IN THIS FILE.
this line is the 1st lower case line in this file.
Two lines above this line is empty.
And this is the last line.

3. 使用grep -A, -B and -C显示之前、之后、前后的几行

当使用grep搜索大文件时,显示匹配行附近的多行数据是一个很有用的功能。


创建如下文件

$ cat demo_text
4. Vim Word Navigation

You may want to do several navigation in relation to the words, such as:

 * e - go to the end of the current word.
 * E - go to the end of the current WORD.
 * b - go to the previous (before) word.
 * B - go to the previous (before) WORD.
 * w - go to the next word.
 * W - go to the next WORD.

WORD - WORD consists of a sequence of non-blank characters, separated with white space.
word - word consists of a sequence of letters, digits and underscores.

Example to show the difference between WORD and word

 * 192.168.1.1 - single WORD
 * 192.168.1.1 - seven words.

4.1 显示匹配行之后的N行

-A

语法:
grep -A  "string" FILENAME


下例显示匹配行和之后的3行数据

$ grep -A 3 -i "example" demo_text
Example to show the difference between WORD and word

* 192.168.1.1 - single WORD
* 192.168.1.1 - seven words.

4.2显示匹配行之前的N行

-B

语法:
grep -B  "string" FILENAME


下例显示匹配行和之前的2行数据

$ grep -B 2 "single WORD" demo_text
Example to show the difference between WORD and word

* 192.168.1.1 - single WORD

4.3显示匹配行前后的N行

-C 显示之前的n行,之后的n行数据.

$ grep -C 2 "Example" demo_text
word - word consists of a sequence of letters, digits and underscores.

Example to show the difference between WORD and word

* 192.168.1.1 - single WORD