Linux Text Processing tool awk

Very good text processing tools, especially variables and control statements, using the awesome.
Personal understanding of the general process is as follows

1. Normal output

# $0表示正行  默认是按照行分割  $1 $2#-----------------------------------------------------------------[[email protected] test]# awk  ‘{print "hello ",$2}‘ fstabhellohellohello  /etc/fstabhello  Created

2. Variables

#FS：input field seperator，  输入  在行里面里面的分割符，默认为空白字符；#OFS：output field seperator，输出  在行里面里面的分割符，默认为空白字符；#-----------------------------------------------------------------[[email protected] test]# awk -F‘ ‘  ‘{print $4}‘ fstab[[email protected] test]# awk -v FS=‘ ‘  ‘{print $4}‘ fstab[[email protected] test]# awk -v FS=‘ ‘ -v OFS=‘:‘  ‘{print $3,$4}‘ fstab   #OFS 相当于把$3,$4  替换成$3 【OFS】$4 by:anaconda

#RS：input record seperator，     输入 默认为行分割符；   #ORS：output record seperator，   输出 默认为行分割符；   （这两个一般很少用，文本从本来一行一行，换成其他格式） #-----------------------------------------------------------------[[email protected] test]# awk -v RS=‘\n‘ -v ORS=‘\n‘  ‘{print $1}‘ fstab   #默认[[email protected] test]# awk -v RS=‘ ‘ -v ORS=‘:‘ ‘{print "hello ",$2}‘ fstab   #hello  #:hello  #:hello   ......

#NF number of field  每行字段数目   $##-----------------------------------------------------------------[[email protected] test]# awk  ‘{print NF}‘ fstab#最后一个字段值#-----------------------------------------------------------------[[email protected] test]# awk  ‘{print $NF}‘ fstab

#NR：number of record, 行号； #-----------------------------------------------------------------[[email protected] test]# awk  ‘{print NR}‘ fstab#FNR：各文件分别计数；行数；#-----------------------------------------------------------------[[email protected] test]# awk  ‘{print FNR}‘ fstab fstab

#自定义变量 -v var=value 变量名区分字符大小写；#-----------------------------------------------------------------[[email protected] test]# awk -v test=‘hello world‘  ‘{print test}‘ fstabhello world[[email protected] test]# awk  ‘{test="hello world"; print  test}‘ fstabhello world

3. The printf command is used to display the style

(1) format must be given;
(2) does not wrap automatically, you need to explicitly give the line-break control, \ n
(3) in format, you need to specify a format symbol for each item that follows.
Format characters:
%c: The ASCII code that displays the characters;
%d,%i: Displays decimal integers;
%e,%e: Numerical display of scientific counting method;
%f: Displayed as floating point number;
%g,%g: Displays values in scientific notation or floating-point form;
%s: Display string;
%u: unsigned integer;
Percent: show% itself;
Modifier:
#[.#]: The width of the first digital control display; The second # indicates the precision after the decimal point;
-: Align Left
+: Display symbols for numeric values

[[email protected] test]# awk   ‘{printf "%50s\n",$1}‘ fstab                                                 #         UUID=7ceb028a-a8b8-467c-b6d4-36910c06c5ac         UUID=3d81b92c-abeb-41f5-8de0-b46d3ffbcf4c         UUID=943c7e04-b733-42fe-a1e2-eabf93693f6b

4. Operator

算术操作符：x+y, x-y, x*y, x/y, x^y, x%y -x +x: 转换为数值；字符串操作符：没有符号的操作符，字符串连接赋值操作符：=, +=, -=, *=, /=, %=, ^=  ++, --     比较操作符：>, >=, <, <=, !=, ==模式匹配符：  ~：是否匹配      !~：是否不匹配逻辑操作符：&&   ||   !函数调用：function_name(argu1, argu2, ...)条件表达式：selector?if-true-expression:if-false-expression#-----------------------------------------------------------------[[email protected] test]# awk -F: ‘{ $7~"/bash" ? is_bash="yes":is_bash="no";age=8+10;print $1,age,$7,is_bash}‘ passwdroot 18 /bin/bash yesbin 18 /sbin/nologin no

5. Delimitation

[[email protected] test]# awk   ‘!/^UUID/{printf "%-50s\n",$1}‘ fstab   #正则[[email protected] test]# awk   ‘/^UUID/{printf "%-50s\n",$1}‘ fstab[[email protected] test]# awk ‘$3>1000{print $1,$3}‘ /etc/passwd      #表达式[[email protected] test]#  awk -F: ‘$NF~"/bash"{print $1,$3}‘ /etc/passwd[[email protected] test]#  awk -F: ‘/^sync/,/^halt/{print $1,$3}‘ /etc/passwdsync 5shutdown 6halt 7[[email protected] test]#  awk -F: ‘(NR>=6&&NR<=8){print NR,$1,$3}‘ /etc/passwd

[[email protected] test]# awk -F: ‘BEGIN{print "username    uid \n---------"}{print $1,$3}‘ /etc/passwdusername    uid---------root 0bin 1daemon 2[[email protected] test]# awk -F: ‘{print "username    uid \n---------";print $1,$3}‘ /etc/passwdusername    uid---------root 0username    uid---------bin 1username    uid

6. Control statements

#if (condition) {statments} [[email protected] test]# awk ' {if (nf>5) print $} '/etc/fstab#if (condition) { Statments} else {statements}[[email protected] test]# awk-f: ' {if ($3>=1000) printf ' Common User:%s\n ', $; else P rintf "root or Sysuser:%s\n", $ '/etc/passwd#-----------------------------------------------------------------# while (Conditon) {statments}[[email protected] test]# awk '/^uuid/{i=1;while (i<=nf) {print $i; i++}} ' Fstab#do Statement while (condition) performs first in judging [[email protected] test]# awk '/^uuid/{i=1;do {print $i; i++;} while (I&LT;=NF)} ' fstab#-----------------------------------------------------------------#for (EXPR1;EXPR2;EXPR3) statement[[email  protected] test]# awk ' {for (i=0;i<nf;i++) {print $i}} ' fstab[[email protected] test]# awk ' begin{names[' a "]=" Zander ";  names["B"]= "Marvin"; for (i in Names) {print i,names[i]}} ' fstab #只能是关联数组 names[0]= ' Zander '; This is also associative array a zanderb marvin#-----------------------------------------------------------------#switch (expression) {case VALUE1 or/regexp/: statement, Case VALUE2 or/regexp2/: statement; ...; default:stat Ement} #next to end the processing of the bank in advance and go directly to the next line; #-----------------------------------------------------------------[[email  Protected] test]# awk-f: ' {if ($3%2!=0) next; print $1,$3} '/etc/passwd

7. Array manipulation

关联数组：array[index-expression]#index in array[[email protected] test]# awk ‘BEGIN{weekdays["mon"]="Monday";weekdays["tue"]="Tuesday"; if("mon" in weekdays){print weekdays["mon"]}else{print "not exist"}}‘Monday#for(var in array) {for-body}[[email protected] test]# awk ‘BEGIN{weekdays["mon"]="Monday";weekdays["tue"]="Tuesday";for(i in weekdays) {print weekdays[i]}}‘统计   去重复[[email protected] test]# netstat -tan | awk ‘/^tcp\>/{state[$NF]++}END{for(i in state) { print i,state[i]}}‘LISTEN 2ESTABLISHED 3

8. Functions

#rand()：返回0和1之间一个随机数；#-----------------------------------------------------------------[[email protected] test]# awk ‘BEGIN{print rand()}‘0.237788#length([s])：返回指定字符串的长度；#-----------------------------------------------------------------[[email protected] test]# awk ‘BEGIN{name="zander"; print length(name)}‘6#sub 替换  -----> 一次#-----------------------------------------------------------------[[email protected] test]# awk ‘BEGIN{name="zander"; print sub("a","A",name),name}‘1 zAnder#sub 替换  -----> 全部#-----------------------------------------------------------------[[email protected] test]# awk ‘BEGIN{name="zandera"; print gsub("a","A",name),name}‘2 zAnderA#split(s,a[,r])：以r为分隔符切割字符s，并将切割后的结果保存至a所表示的数组中；#------------------------------------------------------------------[[email protected] test]# netstat -tan|awk ‘/^tcp\>/{split($5,ip,":"); count[ip[1]]+=1;}END{for(i in count){print i,count[i]}}‘

Linux Text Processing tool awk