The programmer shell with a monthly salary of more than 10000 becomes a grammar skill for secondary school. Do you often use it!!!

One 、 Regular expressions

1、 Introduction to regular expressions

         Regular expressions describe a pattern of string matching （pattern）, It can be used to check whether a string contains some kind of string 、 Replace the matching substring or take a string that meets a certain condition from a string, etc .
         The component that builds a regular expression can be a single character 、 Character set 、 character in range 、 Choice between characters or any combination of all these components

2、 Regular expression symbols

① Basic symbols

Symbol	describe
^	Match the beginning
$	Match the end
[…]	Matches any single character in the set
[^…]	Negate the set
.	Match any single character
*	Match the previous character any number of times
{n,m}	Match the previous character n~m Time
{n,}	Match the previous character at least n Time
{n}	Match the previous character n Time

② Extended regular compatible regular symbols

Regular sign	describe
\b	Match the boundaries of words
\w	Match character numeric underscores
\W	and \w contrary
\s	Match blanks
\d	Match the Numbers
\d+	Match multiple numbers
\D	Match non numeric

3、grep Grammar format

grep    Options    Matching mode    file

Common options ：
-v: Reverse match
-i： Ignore letter case

Two 、sed

1、sed What is it? ？

         sed Is a non interactive streaming editor , You can add, delete, modify and query text , Mainly used to automatically edit one or more files 、 Simplify file manipulation 、 Write conversion program, etc

2、sed elements of grammar

Format ：
      · sed    [ Options ]    ‘[ Locator ] Instructions ’    file name

      · sed    [ Options ]    ‘[ Locator ] Instructions ’
Common options ：
-n： Mask default output
-i： Modify the source file directly （sed The source file will not be modified by default , Only the results will be printed )
-r： Support extended regularization

① Line number locator

         sed You can use the line number to locate the data content you need to modify

 example ：sed -n "3p" /etc/passwd	// Print /etc/passwd pass the civil examinations 3 That's ok 

② Regular locator

         sed You can use regular matching to match the data you need , Then edit the corresponding content

 example ： sed -n "/^root/p" /etc/passwd

③ sed Multi line text processing

Commonly used instructions ：

i(insert)：     Insert
a(append)：     Additional
r(read)：               Read the file | Import file content
w(write)：                file save as | Export file content

3、 ... and 、awk Process control

1、awk What is it? ？

       awk Is a language that processes text , Is a powerful text analysis tool , Is a powerful line by line processing software , Read one line at a time , Match the regular and then process , Check input text based on pattern matching , Line by line processing and output , Usually used for re shell Script , Get the specified data . When used alone , Statistics can be made on the text data

2、awk Command format

Format ：
      · Front order    |   [ Options ]    ‘[ Conditions ]{ Instructions }’
      ·awk    [ Options ]    ‘[ Conditions ]{ Instructions }’    file
Common options ：
-F： You can specify the separator , The default separator is （ Space or Tab key ）

① awk Built-in variables （ Built in variables have special meanings , You can use it directly

Variable	describe
FS	Save or set field separator , for example FS=":" , And -F Function as
$n	Specify the number of divisions n A field , Such as $1、$3 Separate indication control 1、 The first 3 Column
$0	The entire line of text currently read
NF	Record the number of fields in the current processing line （ Number of columns ）
NR	Record the number of currently read rows （ Row number ）

② awk Filtering time

     Format :    awk ‘BEGIN{}    [ Conditions ]{}    END{}’     file

• BEGIN{}     Process before all lines , Execute... Before reading the first line of text , Generally used to initialize
• {}      Deal with line by line , Read the text line by line and perform the corresponding processing ,
• END{}     Execute... After processing the last line of text , Generally used to output results