Classical 10 Examples for learning AWK

• 作者：柳大·Poechant（钟超）
• 邮箱：zhongchao.ustc#gmail.com（# -> @）
• 博客：Blog.CSDN.net/Poechant
• 日期：June 9^th, 2012

Example 1: Formatting Fields Into Columns

countries文件：

Canada:3852:25:North America
USA:3615:237:North America
Brazil:3286:134:South America
England:94:56:Europe
France:211:55:Europe
Japan:144:120:Asia
Mexico:762:78:North America
China:3705:1032:Asia
India:1267:746:Asia

What do you want?

将 countries 文件的每一行按照指定格式输出。

Command

awk -F: '{ printf "%-10s\t %d\t %d\t %15s\n",$1,$2,$3,$4 }' countries

Result:

Canada      3852    25        North America 
USA         3615    237       North America 
Brazil      3286    134       South America 
England     94  56                   Europe 
France      211     55               Europe 
Japan       144     120                Asia 
Mexico      762     78        North America 
China       3705    1032               Asia 
India       1267    746                Asia

Analysis:

• -F后面接分隔符，这里是冒号。
• 对齐由正负号表示，不显式指明，则继承之前的对齐方式。
• 字符串是s，同 standard c 的 stream format。
• 整数是d，同 standard c 的 stream format。
• 正则表达式，用''单引号括起来，再用{}花括号括起来，具体的后面会了解。

Example 2: Selecting Records

countries文件：同 Example 1。

What do you want?

含有`Europe`关键词的行全部输出。

Command:

 awk '/Europe/' countries 

Result:

England:94:56:Europe
France:211:55:Europe

Analysis:

• 包含Europe的关键词的行。
• 必须用//括起来。

Eample 3: Comparators

countries文件：同 Example 2。

What do you want?

第三列值为 55 的行全部输出。

Command:

 awk -F: '$3 == 55' countries 

Result:

France:211:55:Europe

Analysis：

• $#表示指定某一列。
• ==比较运算符可用。其他比较运算符：
  

  • != not equal to
  • > greater than
  • < less than
  • >= greater than or equal to
  • <= less than or equal to

Exmaple 4: Using Logical Operators (and, or) to create multiple conditions

cars文件：

ford     mondeo  1990   5800
ford     fiesta  1991   4575
honda    accord  1991   6000
toyota   tercel  1992   6500
vaxhaull astra   1990   5950
vaxhaull carlton 1991   6450

Command:

awk '$3 >=1991 && $4 < 6250' cars

Result:

ford     fiesta  1991   4575
honda    accord  1991   6000    

Analysis:

• &&
• ||

Example 5: How to run an AWK program file?

Input file: cars in the above example.

Program file: hello

#!/usr/bin/awk
{
    x = "hello"
    print x
}

Command:

awk -f hello cars

Result:

hello
hello
hello
hello
hello
hello

Analysis:

• Output hello instead of each record(line).

Reference:

http://www.delorie.com/gnu/docs/gawk/gawk_11.html

Example 6: Boost up your AWk program: Use Variables!

Input file: countries in the example 4

Program file:

#!/usr/bin/awk
{
    x = "hello"
    print x
}

Command:

awk -f hello countries

Result:

USA:3615:237:North America
Brazil:3286:134:South America
England:94:56:Europe
France:211:55:Europe
Japan:144:120:Asia
Mexico:762:78:North America
China:3705:1032:Asia
India:1267:746:Asia

Analysis:

• $0 means the current record

Example 7: Use internal variables!

Input file: countries in the example 4

Program file: hello

#!/usr/bin/awk                                                                                                              

{
    print FILENAME OFS \
        NR OFS \
        $1 OFS \
        $2 OFS \
        $3 OFS \
        $4 OFS \
        ORS 
}

Command: