Awk advanced applications

1. If condition judgment

   Syntax 1
   

   If (expression)

   Action 1

   Else

   Action 2

   Syntax 2

   If (expression) Action 1; else action 2

   # An alarm is triggered when the available capacity of the boot partition is less than 20 mb. Otherwise, OK is displayed.
   

   DF | grep 'boot' | awk '{if ($4 <20000) print "alart"; else print "OK "}'
   

2. While Loop

   Syntax 1

   While (condition)

   Action

   Example:

   X = 1

   While (I <10 ){

   Print $1
   

   }

   Example:

   Awk 'I = 1 {} begin {While (I <= 10) {++ I; print I} 'test.txt
   

   Syntax 2

   Do

   Action

   While (condition)

   Example:
   

   Awk 'in in {do {++ X; print x} while (x <= 10)} 'test.txt

3. For Loop

   For (variable; condition; Counter)

   Action

   Example:

   Awk 'in in {for (I = 1; I <= 10; I ++) print I} 'test.txt
   Awk 'in in {for (I = 10; I> = 1; I --) print I} 'test.txt

4. Break and continue

   Break bounce cycle

   Continue ends the current loop

   For (I = 1; I <= 10; I ++ ){

   If (I = 5)

   Continue

   Print I
   

   }

   For (I = 1; I <= 10; I ++ ){

   If (I = 5)

   Break
   

   Print I

   }

5. Function

   5.1 rand () Functions

   Awk 'in in {print rand (); print srand ()} 'test.txt
   

   5.2 gsub (x, y, z) Functions

   In string Z, use string y to replace all strings that match the regular expression X. The default value of Z is $0.

   Awk-F: 'gsub (/root/, "CCC", $0) {print $0} '/etc/passwd
   CCC: X: 0: 0: CCC:/bin/bash
   

   5.3 sub (x, y, z) Functions

   In string Z, use string y to replace the first string that matches Regular Expression X. The default value of Z is $0.

   Awk-F: 'sub (/CCC/, "root", $0) {print $0} '/etc/passwd
   CCC: X: 0: 0: CCC:/bin/bash
   

   5.4 length (z) Function

   Purpose: display the length of each line in the test.txt document:
   

   Awk '{print length ()}'/usr/local/src/Allen/test.txt
   

   5.5 Getline () function

   DF-H | awk '{If (NF = 1) {Getline; print $3}; If (NF = 6) Print $4 }'

   DF-H | awk 'in in {print "Disk Free :"}\

   {If (NF = 1) {Getline; print $3}; If (NF = 6) {print $4 }}'
   

   
   

This article from the "quiet fan Yin" blog, please be sure to keep this source http://mastters.blog.51cto.com/6516495/1532880