Shell script, awk uses if, for process control

Shell Script ,awk Process control , Support for,if etc.

One 、 Single branch if Judge
1、awk ‘{ Instructions }’ dir
awk -F: ‘BEGIN{x=0} {if($3>=1000){i++}}END{print i}’ /etc/passwd
In the statistical file uid Greater than or equal to 1000 Quantity of content .

2、awk -F: ‘{if($1==“root”){print $1,$3}}’ /etc/passwd
awk The style is similar to the programming language , Constants use double quotation marks , You can't use single quotes or backquotes

Two 、 Multiple branches if Judge
1、 Double branch if…else
awk -F: ‘{if($3>=1000){i++}else{j++}} END{print i,j}’ /etc/passwd
Judge uid1000 The number of users and 1000 The number of users below

2、 Multiple branches ,if…else if…else
awk -F: ‘{if($30){print $1}else if($31000){print $1}else{print $7}}’ /etc/passwd

3、 ... and 、for loop ,awk Of for use c The grammatical format of a language
awk ‘BEGIN{for(i=1;i<=5;++i){print i}}{print}’ /etc/passwd
Print numbers before printing user information 1-5

Four 、awk Arrays and Applications
1、 Define an array
Format ： Array name [ Subscript ]= Element value
awk ‘BEGIN{name[0]=“TOM”;name[1]=“JERRY”;print name[0],name[1]}’
Be careful print The following variables are used , Separate , Will print separately with spaces on the same line , If you use a semicolon and write two print, Two lines of content will be printed separately .

2、 Call array
Array name [ Subscript ]

3、 Traversal array
for( Variable name in Array name ){print Array name [ Variable ]}

The definition of an array cannot be name=“1234”,print name[1], This is used in awk There are grammatical errors in

Example ：
1、awk ‘BEGIN{name[0]=“TOM”;name[1]=“JERRY”;print name[0],name[1]}’
Print... On the screen TOM,JERRY

2、awk ‘{array[$1]++}END{for(i in array){print i,array[i]}}’ dir
Print the number of repetitions of the contents of the first column in the specified file