首先创建示例文件
$ 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１　从单个文件中搜索特定字符串
Syntax:
grep "literal_string" filename
$ grep "this" demo_file
this line is the 1st lower case line in this file.
Two lines above this line is empty.
例２　在多个文件中检查特定字符串
Syntax:
grep "string" FILE_PATTERN

$ 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３　忽略大小写
Syntax:
grep -i "string" FILE

$ 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４　正则表达式匹配
Syntax:
grep "REGEX" filename

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

From documentation of grep: A regular expression may be followed by one of several repetition operators:

? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{,m} The preceding item is matched at most m times.
{n,m} The preceding item is matched at least n times, but not more than m times.

例５　全单词匹配　Checking for full words, not for sub-strings using grep -w
$ 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.

$ 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６　显示之前之后或者临近行
Displaying lines before/after/around the match using grep -A, -B and -C

先创建对应文件
$ 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.


6.1 Display N lines after match
-A is the option which prints the specified N lines after the match as shown below.
Syntax:
grep -A <N> "string" FILENAME

$ 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 Display N lines before match
-B is the option which prints the specified N lines before the match.

Syntax:
grep -B <N> "string" FILENAME

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

* 192.168.1.1 - single WORD


6.3 Display N lines around match
-C is the option which prints the specified N lines before the match. In some occasion you might want the match to be appeared with the lines from both the side. This options shows N lines in both the side(before & after) of match.

$ 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７　高亮显示
$ 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８　搜索所有文件
Searching in all files recursively using grep -r

$ grep -r "ramesh" *

例９　搜索非匹配内容
Invert match using grep -v
$ 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　多个表达式非匹配
display the lines which does not matches all the given pattern.
Syntax:
grep -v -e "pattern" -e "pattern"

$ cat test-file.txt
a
b
c
d

$ grep -v -e "a" -e "b" -e "c" test-file.txt
d

例１１　计数求和
Counting the number of matches using grep -c
Syntax:
grep -c "pattern" filename

$ grep -c "go" demo_text
6

When you want do find out how many lines that does not match the pattern

$ grep -v -c this demo_file
4
例１２　只显示匹配的文件名称
$ grep -l this demo_*
demo_file
demo_file1

例１３　显示匹配内容在行内的位置
Syntax:
grep -o -b "pattern" file

$ cat temp-file.txt
12345
12345

$ grep -o -b "3" temp-file.txt
2:3
8:3

例１４　显示行号
$ 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.