Grep命令主要用于從文件中查找指定的字符串。
首先建一個demo_file:
$ cat 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.
例01:從單個文件中查找指定的字符串
$ grep "this" demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
例02:從多個文件中查找指定的字符串
$ cp demo_file demo_file1
$ grep "this" demo_*
demo_file:this line is the 1st lower case line in this file.
demo_file:Two lines above this line is empty.
demo_file:And this is the last line.
demo_file1:this line is the 1st lower case line in this file.
demo_file1:Two lines above this line is empty.
demo_file1:And this is the last line.
例03:忽略大小寫使用 grep -i
$ grep -i "the" 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.
And this is the last line.
例04:在文件中匹配正則表達式
如果你能在實際使用正則表達式，能使效率大大提高。在下面的例子中，匹配了所有以lines開頭，以empty結尾的行。
$ grep "lines.*empty" demo_file
Two lines above this line is empty.
從Grep文檔的來看，一個正則表達式必須遵循下面的匹配操作。
1.? The preceding item is optional and matched at most once.
2.* The preceding item will be matched zero or more times.
3.+ The preceding item will be matched one or more times.
4.{n} The preceding item is matched exactly n times.
5.{n,} The preceding item is matched n or more times.
6.{,m} The preceding item is matched at most m times.
7.{n,m} The preceding item is matched at least n times, but not more than m times.
例05:用grep -w來查找全匹配，不包括子字符串
比如說:用下面的例子搜索出來的例子包括"is","his"
$ 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.
而用grep -iw搜索出來的結果如下: 注意，忽略大小。"IS","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.
例06:用grep -A,-B,-C 來查看after/before/around 行
當在一個大的文件中執行grep操作時，如果想要看其中一些行，并且想看之前，之后的或某些行附近的，那么這里命令就起作用了。grep -A,-B,-C.先建個demo.txt作為模板
$ 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.
6.1 顯示匹配后N行
$ 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.
6.2 顯示匹配前N行
$ grep -B 2 "single WORD" demo_text
Example to show the difference between WORD and word
* 192.168.1.1 - single WORD
6.3 顯示匹配前N行
$ 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
例07:用GREP_OPTIONS來讓查找的項醒目
如果你想使匹配的好看且醒目，可以使用下面的操作:
$ export GREP_OPTIONS='--color=auto' GREP_COLOR='100;8'
$ grep this demo_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.
例08:用grep -r來搜索所有的文件及子目錄
$ grep -r "ramesh" *
例09:用grep -v來顯示不匹配的項
$ grep -v "go" demo_text
4. Vim Word Navigation
You may want to do several navigation in relation to the words, such as:
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.
例10:顯示所有不匹配的項
$ cat test-file.txt
a
b
c
d
$ grep -v -e "a" -e "b" -e "c" test-file.txt
d
例11:用grep -c 來計算匹配的數量
11.1計算匹配的字符串數
$ grep -c "go" demo_text
6
11.2計算匹配的模式數
$ grep -c this demo_file
3
11.3計算不匹配的模式數
$ grep -v -c this demo_file
4
例12:使用grep -l顯示匹配的文件名
$ grep -l this demo_*
demo_file
demo_file1
例13:只顯示匹配的字符串
$ grep -o "is.*line" demo_file
is line is the 1st lower case line
is line
is is the last line
例14:
$ cat temp-file.txt1234512345
$ grep -o -b "3" temp-file.txt
2:3
8:3
注意:上述的不是該字符所在行中的位置，而是字節的位置。
例15:用grep -n 顯示行數
$ grep -n "go" demo_text
5: * e - go to the end of the current word.
6: * E - go to the end of the current WORD.
7: * b - go to the previous (before) word.
8: * B - go to the previous (before) WORD.
9: * w - go to the next word.
10: * W - go to the next WORD.
