一、基本知识

NR: 文件中记录个数

NF：每一行字段个数

二、测试文件内容

test.txt:

zhangsan  20
lisi      19
wangwu    21

三、测试结果

1.  awk '{print NR,$1,NF}' test.txt 

1 zhangsan 2
2 lisi 2
3 wangwu 2

2. awk '$2 >= 20 {print $1,$2}' test.txt 

zhangsan 20
wangwu 21

3. awk '$2 >= 20 {print "name:", $1,"age:", $2}' test.txt 

name: zhangsan age: 20
name: wangwu age: 21

4. awk '$2 >= 20 {printf("name: %s    age: %d\n", $1, $2)}' test.txt

name: zhangsan    age: 20
name: wangwu    age: 21

5. awk '$2 >= 20 {printf("name: %s    age: %.1f\n", $1, $2)}' test.txt

name: zhangsan    age: 20.0
name: wangwu    age: 21.0

6. awk '{printf("name: %s    age: %.1f\n", $1, $2)}' test.txt  | sort

name: lisi    age: 19.0
name: wangwu    age: 21.0
name: zhangsan    age: 20.0

7. awk '$2 > 20' test.txt

wangwu    21

8. awk '$2==20' test.txt 

zhangsan  20

9. awk '$2==20 || $1=="lisi"' test.txt

zhangsan  20
lisi      19

10. awk '/w/' test.txt

wangwu    21

11. awk 'NR > 1 {print "name:", $1,"age:", $2}' test.txt 

name: lisi age: 19
name: wangwu age: 21

12. awk 'BEGIN {print "Name    Age"} {print}' test.txt

Name    Age
zhangsan  20
lisi      19
wangwu    21

13. awk 'BEGIN {print "Name    Age"} $2 > 19 {print} END {print "Count: ", NR}' test.txt

Name    Age
zhangsan  20
wangwu    21
Count:  3

14. awk 'BEGIN {print "Name    Age"} $2 > 19 {print;count=count+1} END {print count}' test.txt

Name    Age
zhangsan  20
wangwu    21
2

15:awk 'BEGIN {print "Name    Age"} $2 > 19 {print;count=count+1} END {if(count > 0) print count ;else print 0}' test.txt

Name    Age
zhangsan  20
wangwu    21
2

16. awk 'BEGIN {print "Name    Age"} $2 > 19 {print;count=count+1} END {if(count < 0) print count ;else print 0}' test.txt

Name    Age
zhangsan  20
wangwu    21
0

17. awk 'BEGIN {print "Name    Age"} $2 > 19 {print;count=count+1} END {if(count > 0) for(i=0;i<count;i++) print i }' test.txt

Name    Age
zhangsan  20
wangwu    21
0
1

18.