Awk of shell script

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Preface

What is? AWK

WK Is a language for processing text files , Is a powerful text analysis tool . It is a programming language specially designed for text processing , It's also line processing software , Usually used to scan 、 Filter 、 Count and summarize the work quantity , It can come from standard input, pipe or file

20 century 70 Was born in Bell Laboratories , Now? centos7 It's using gawk, The name AWK Because it took three founders Alfred Aho,Peter Weinberger, and l Brian Kernighan Of Family Name First character .

working principle :

When you read the first line , Matching condition , Then perform the specified action , Then read the second line of data processing , No default output , If no matching criteria are defined, the default is to match all data rows ,awk Implicit loop , The action will be executed as many times as the condition matches .

Read text line by line , The default is space or tab Key to separate the separator , Save the separated fields to the built-in variables , And execute the edit command according to the mode or condition .
sed Commands are often used for a whole line of processing , and awk They tend to divide a line into multiple "“ Field " And then deal with it ..awk Information is also read line by line , The execution result can be obtained through print To print and display field data .
In the use of awk In the course of the order , You can use logical operators ”&&“ Express " And ”、"|| Express " or "、"!“ Express non ” ; You can also do simple mathematical operations , Such as +、-、*、/、%、^ Respectively means plus 、 reduce 、 ride 、 except 、 Remainder and power .

awk Built-in variables

FS: Specify the field separator for each line of text , The default is space or tab stop 
NF: Number of fields in the row currently processed 
NR: Line number of the currently processed line ( Ordinal number )
$0: The entire contents of the currently processed row 
$n: Of the current processing line n A field ( The first n Column )
FTLENAME： File name processed 
RS： Line separator ,awk Read the reference room from the file , The price is based on RS The definition of cut data into many records ,
 and awk Read only one record at a time , To deal with . The default is “\n”
 Jane said ： Data record separation , The default is \n, One record for each action 

awk -F : '{print $1}' xy   
## Print xy The first column of the text , And ： Separator 

awk -F : '{print $1,$2}' xy   
## Print xy The first and second columns of the text , And ： Separator 
 Separate with commas , Display with space effect 

awk -F: '/home/{print $0}' xy  
## The print contains home The whole line of 

awk -F: '/home/{print $1}' xy  
## The print contains home The first column 

awk -F[:/] '{print NF}' xy  
## Statistics to ： and / As a separator , How many columns are there 

awk -F[:/] '{print NR}' xy  
## According to the line Numbers 

awk ‘NR==10’ xy  
## Display the entire tenth line 

awk -F: 'NR==10{print $1}' xy  
## With : Separator , Print the first column of the tenth row 

awk -F: 'NR==10{print $NF}' xy  
## Print the last column of the tenth row 

awk 'END{print NR}' xy  
## The statistical number of rows 

ifconfig ens33 |awk '/netmask/{print $2}'  
## Print this machine IP Address 

ifconfig ens33| awk '/RX p/{print $5}'  
## Print the current flow 

 Line by line what tasks to perform before starting , What tasks will be performed after the end of , use "BEGIN、END"
BEGIN Generally used for initialization , Read the data only once before 
END It is generally used for summary operation , Execute only once after reading the data record 

awk 'BEGIN{FS=":";OFS="---"}{print $1,$2}' xy  
##OFS Define how the output is separated ,$1$2 The middle should be separated by commas , Because commas are mapped to by default OFS Variable , This variable defaults to a space 

awk Arithmetic

Fuzzy matching , use ~ Means to contain , !~ Does not include

 awk -F: '$1~/ro/{pring $2}' xy  
 ## Print the first column containing ro The second column of the row , With : Separate 

 awk -F: '$1!~/ro/{pring $2}' xy  
 ## The first column printed does not contain ro The second column of the row , With : Separate 

awk -F: '$1=="xy"' xy  
## Print... Equals the first column xy The line of 

awk -F: '$3>=1000' xy  
## Print the third column greater than or equal to 1000 The line of 

awk -F: '$3<10 || $3>=1000' xy  
## Print the third column less than 10, Or the third column is greater than 1000 The line of 

awk -F: '$3>10 && $3<=1000' xy  
## Print the third column greater than 10 And less than 1000 The line of 

awk  'NR>2 && NR<9' xy  
## Print line number is greater than 2 Less than 9 Entire line of 

seq 200 | awk '$1%7==0 && $1~/7/'  
## Print the first column divided by 7 Take remainder equal to 0 And the first column contains 7 The line of 

awk '{print FNR,$0}' xy /etc/passwd   
## Display the line numbers of the two files separately ,NR The line numbers of two texts will be displayed in order , Will not recalculate 

awk 'BEGIN{RS=":"}{print $0}' xy  
## Every time I meet : Just wrap and continue to show 

awk 'BEGIN{ORS=" "}{print $0}' xy  
## Merge multiple rows into one row , When outputting, separate each line with a space , Customizable 

awk Advanced usage

awk -v b="$a" 'BEGIN{print b}'  
## Set the system variables a, stay awk Assign a value to a variable b, Then call the variable b

awk 'BEGIN{print "'$a'"}'    
 ## Direct call requires double quotation marks first and then single quotation marks 
 
awk -vc=1 'BEGIN{print c}'    
##awk Directly define and reference 

 Call function getline, When reading a row of data, you do not get the current row, but the next row of the current row 

awk -F: '{if($3<10){print $0}}' /etc/passwd  ## Print the third column less than 10 Entire line of 

awk -F: '{if($3<10){print $2}else{print $5}}' xy
## The third column is less than 10, Print the second column , Otherwise, print the fifth column 

awk And support for loop ,while loop , function , Array etc. 
awk 'BEGIN{x=0};/\/bin\/bash$/ {x++;print x,$0};END {print x}' /etc/passwd  
##x=0 Is to define variables ,/\/bin\/bash$/ In order to /bin/bash The line at the end ,x++ Add... Every time 1,print x,$0, Print... For each cycle x Value and the entire line ,END End operation   final print x Indicates the total number of rows that meet the conditions or the number of cycles 
grep -c "/bin/bash$" /etc/passwd  ## Statistics to /bin/bash How many lines are there at the end 

Ternary operator

awk -F: ‘{mak=($3>$4) ?$3:$4; {print mak}}’ xy ##$3>$4) ?$3:$4 Ternary operator , If the value of the third column is greater than the value of the fourth column , Then assign the third column to max, Otherwise, assign the fourth column to max

awk -F: ‘($1~“root”) && (NF==7) {print $0}’ /etc/passwd
## The first column contains root And the number of columns is equal to 7, Print the entire line

Through pipes 、 Double quotes call shell command
echo $PATH| awk ‘BEGIN{RS=":"};END {print NR}’
echo $PATH| awk ‘BEGIN{RS=":"};{print NR,$0};END {print NR}’
## Count the number of colon separated text paragraphs ,END{} In the block , Often put in the print results and other statements

Memory
View the current memory usage percentage

free -m |awk '/Mem:/{print int($3/($3+$4)*100)"%"}'
free -m |awk '/Mem:/{print $3/$2}'0.327869
free -m |awk '/Mem:/{print $3/$2*100}'32.7869
free -m |awk '/Mem:/{print $3/$2*100}'32
free -m |awk '/Mem:/{print $3/$2*100}'
free -m |awk '/Mem:/{print int($3/$2*100)"%"}'32

free -m |awk ‘/Mem:/ {print $3/$2*100}’ | awk -F. ‘{print $1 “%”}’

top -b -n 1 |grep Cpu|awk -F ‘,’ ‘{print $4}’ | awk ‘{print $1}’ ## View the current CPU Idle rate ,（-b -n 1 It means that you only need 1 The output of this ）

date -d “$(awk -F “.” ‘{print $1}’ /proc/uptime) second ago”+"%F %H:%M:%S"
## Display the last system restart time , Equate to uptime;second ago To show how many seconds ago .

summary

One of the three Internet swordsmen awk Usage of