shell编程系列17--文本处理三剑客之awk动作中的表达式用法
awk动作表达式中的算数运算符
awk动作中的表达式用法总结：
运算符 含义
+ 加
- 减
* 乘
/ 除
% 模
^或** 乘方
++x 在返回x变量之前，x变量加1
x++ 在返回x变量之后，x变量加1
--x 在返回x变量之前，x变量减1
x-- 在返回x变量之后，x变量减1
1、使用awk计算/etc/services中的空白行数量
awk 'BEGIN{sum=0}/^$/{++sum}END{print sum}' /etc/services
2、计算学生课程分数平均值，学生课程文件内容如下：
Allen 80 90 96 98
Mike 93 98 92 91
Zhang 78 76 87 92
Jerry 86 89 68 92
Han 85 95 75 90
Li 78 88 98 100
# 代码如下：
[root@localhost shell]# awk 'BEGIN{printf "%-20s%-20s%-20s%-20s%-20s%-20s\n","Name","Chinese","English","Math","Physical","Average"}{sum=$2+$3+$4+$5;avg=sum/4}{printf "%-20s%-20d%-20d%-20d%-20d%-0.2f\n",$1,$2,$3,$4,$5,avg}' student.txt
Name Chinese English Math Physical Average
Allen 80 90 96 98 91.00
Mike 93 98 92 91 93.50
Zhang 78 76 87 92 83.25
Jerry 86 89 68 92 83.75
Han 85 95 75 90 86.25
Li 78 88 98 100 91.00
[root@localhost shell]# awk 'BEGIN{num1=20;num2+=num1;print num1,num2}'
20 20
[root@localhost shell]# awk 'BEGIN{num1=20;num2=30;print num1+num2}'
50
[root@localhost shell]# awk 'BEGIN{num1=20;num2=30;print num1-num2}'
-10
[root@localhost shell]# awk 'BEGIN{num1=20;num2=30;print num1*num2}'
600
[root@localhost shell]# awk 'BEGIN{num1=20;num2=30;print num1/num2}'
0.666667
# 保留小数后两位
[root@localhost shell]# awk 'BEGIN{num1=20;num2=30;printf "%0.2f\n",num1/num2}'
0.67
[root@localhost shell]# awk 'BEGIN{num1=20;num2=3;printf "%0.2f\n",num1**num2}'
8000.00
# 打印
[root@localhost shell]# awk 'BEGIN{num1=20;num2=3;printf "%0.2f\n",num1^num2}'
8000.00
#
[root@localhost shell]# awk 'BEGIN{x=20;y=x++;print x,y}'
21 20
[root@localhost shell]# awk 'BEGIN{x=20;y=++x;print x,y}'
21 21
[root@localhost shell]# awk 'BEGIN{x=20;y=--x;print x,y}'
19 19
[root@localhost shell]# awk 'BEGIN{x=20;y=x--;print x,y}'
19 20
# 输出平均值
[root@localhost shell]# cat student.txt
Allen 80 90 96 98
Mike 93 98 92 91
Zhang 78 76 87 92
Jerry 86 89 68 92
Han 85 95 75 90
Li 78 88 98 100
[root@localhost shell]# awk '{total=$2+$3+$4+$5;AVG=total/4}{printf "%-8s%-5d%-5d%-5d%-8d%0.2f\n",$1,$2,$3,$4,$5,AVG}' student.txt
Allen 80 90 96 98 91.00
Mike 93 98 92 91 93.50
Zhang 78 76 87 92 83.25
Jerry 86 89 68 92 83.75
Han 85 95 75 90 86.25
Li 78 88 98 100 91.00
# 加上标题并格式化输出
[root@localhost shell]# awk 'BEGIN{printf "%-10s%-10s%-10s%-10s%-10s%-10s\n","name","Yuwen","math","English","Pysical","Average"}{total=$2+$3+$4+$5;AVG=total/4}{printf "%-10s%-10d%-10d%-10d%-10d%-10.2f\n",$1,$2,$3,$4,$5,AVG}' student.txt
name Yuwen math English Pysical Average
Allen 80 90 96 98 91.00
Mike 93 98 92 91 93.50
Zhang 78 76 87 92 83.25
Jerry 86 89 68 92 83.75
Han 85 95 75 90 86.25
Li 78 88 98 100 91.00
