Shell编程之运算

一、变量的数值计算

1.算术运算符

常用的运算符号

常用的运算命令

（1）双小括号

基本语法

1）利用“(())”进行简单运算

[root@codis-178 ~]# echo $((1+1))
2
[root@codis-178 ~]# echo $((6-3))
3
[root@codis-178 ~]# ((i=5))
[root@codis-178 ~]# ((i=i*2))
[root@codis-178 ~]# echo $i
10

2）利用“(())”进行复杂运算

[root@codis-178 ~]# ((a=1+2**3-4%3))
[root@codis-178 ~]# echo $a
8
[root@codis-178 ~]# b=$((1+2**3-4%3))
[root@codis-178 ~]# echo $b
8
[root@codis-178 ~]# echo $((1+2**3-4%3))
8
[root@codis-178 ~]# a=$((100*(100+1)/2))
[root@codis-178 ~]# echo $a
5050
[root@codis-178 ~]# echo $((100*(100+1)/2))
5050

3）特殊运算符的运算

[root@codis-178 ~]# a=8
[root@codis-178 ~]# echo $((a=a+1))
9
[root@codis-178 ~]# echo $((a+=1))
10
[root@codis-178 ~]# echo $((a**2))
100

4）比较和判断

[root@codis-178 ~]# echo $((3<8))
1
[root@codis-178 ~]# echo $((8<3))
0
[root@codis-178 ~]# echo $((8==8))
1
[root@codis-178 ~]# if ((8>7&&5==5))
> then
> echo yes
> fi
yes

5）在变量前后使用--和++特殊运算符的表达式

[root@codis-178 ~]# a=10
[root@codis-178 ~]# echo $((a++))
10
[root@codis-178 ~]# echo $a
11
[root@codis-178 ~]# a=11
[root@codis-178 ~]# echo $((a--))
11
[root@codis-178 ~]# echo $a
10
[root@codis-178 ~]# a=10
[root@codis-178 ~]# echo $a
10
[root@codis-178 ~]# echo $((--a))
9
[root@codis-178 ~]# echo $((++a))
10
[root@codis-178 ~]# echo $a
10

6）通过“(())”运算后赋值给变量

[root@codis-178 ~]# myvar=99
[root@codis-178 ~]# echo $((myvar+1))
100
[root@codis-178 ~]# echo $((   myvar+1   ))
100
[root@codis-178 ~]# myvar=$((myvar+1))
[root@codis-178 ~]# echo $myvar
100

7）包含“(())”的各种常见运算

[root@codis-178 ~]# echo $((6+2))
8
[root@codis-178 ~]# echo $((6-2))
4
[root@codis-178 ~]# echo $((6*2))
12
[root@codis-178 ~]# echo $((6/2))
3
[root@codis-178 ~]# echo $((6%2))
0
[root@codis-178 ~]# echo $((6**2))
36

8）在shell脚本中的示例

[root@codis-178 ~]# cat test.sh
#!/bin/bash

a=6
b=2

echo "a-b=$(($a-$b))"
echo "a+b=$(($a+$b))"
echo "a*b=$(($a*$b))"
echo "a/b=$(($a/$b))"
echo "a**b=$(($a**$b))"
echo "a%b=$(($a%$b))"

[root@codis-178 ~]# sh test.sh
a-b=4
a+b=8
a*b=12
a/b=3
a**b=36
a%b=0

9）将上面的脚本中a、b两个变量通过命令行脚本传参，以实现混合运算

[root@codis-178 ~]# cat test.sh
#!/bin/bash

a=$1
b=$2

echo "a-b=$(($a-$b))"
echo "a+b=$(($a+$b))"
echo "a*b=$(($a*$b))"
echo "a/b=$(($a/$b))"
echo "a**b=$(($a**$b))"
echo "a%b=$(($a%$b))"

[root@codis-178 ~]# sh test.sh 8 3
a-b=5
a+b=11
a*b=24
a/b=2
a**b=512
a%b=2

[root@codis-178 ~]# sh test.sh 3 6
a-b=-3
a+b=9
a*b=18
a/b=0
a**b=729
a%b=3

10）实现输入2个数进行运算的计算器

[root@codis-178 ~]# cat yunsuan.sh
#!/bin/bash

print_usage(){
	printf "Please enter an integer\n"
	exit 1
}
read -p "Please input first number: " firstnum
if [ -n "`echo $firstnum|sed 's/[0-9]//g'`" ];then
	print_usage
fi
read -p "Please input the operators: " operators
if [ "${operators}" != "+" ] && [ "${operators}" != "-" ] && [ "${operators}" != "*" ] && [ "${operators}" != "/" ];then
	echo "please use (+|-|*|/)"
	exit 2
fi
read -p "Please input second number: " secondnum
if [ -n "`echo $secondnum|sed 's/[0-9]//g'`" ];then
	printf_usage
fi
echo "${firstnum}${operators}${secondnum}=$((${firstnum}${operators}${secondnum}))"
[root@codis-178 ~]# sh yunsuan.sh
Please input first number: 5
Please input the operators: +
Please input second number: 16
5+16=21
[root@codis-178 ~]# sh yunsuan.sh
Please input first number: 9
Please input the operators: *
Please input second number: 24
9*24=216
[root@codis-178 ~]# sh yunsuan.sh
Please input first number: 76
Please input the operators: -
Please input second number: 24
76-24=52

改良版

[root@codis-178 ~]# cat yunsuan1.sh
#!/bin/bash

print_usage(){
	printf $"USAGE:$0 NUM1 {+|-|*|/} NUM2\n"
	exit 1
}
if [ $# -ne 3 ]
	then
		print_usage
fi
firstnum=$1
secondnum=$3
op=$2
if [ -n "`echo $firstnum|sed 's/[0-9]//g'`" ];then
	print_usage
fi
if [ "$op" != "+" ] && [ "$op" != "-" ] && [ "$op" != "*" ] && [ "$op" != "/" ]
	then
		print_usage
fi
if [ -n "`echo $secondnum|sed 's/[0-9]//g'`" ];then
	printf_usage
fi
echo "${firstnum}${op}${secondnum}=$((${firstnum}${op}${secondnum}))"
[root@codis-178 ~]# sh yunsuan1.sh 6 + 8
6+8=14
[root@codis-178 ~]# sh yunsuan1.sh 56 + 13
56+13=69
[root@codis-178 ~]# sh yunsuan1.sh 56 - 13
56-13=43

[root@codis-178 ~]# sh yunsuan1.sh 2 * 2
USAGE:yunsuan1.sh NUM1 {+|-|*|/} NUM2
[root@codis-178 ~]# sh yunsuan1.sh 9 / 3
9/3=3
[root@codis-178 ~]# sh yunsuan1.sh 2 \* 2  # 乘号需要转义
2*2=4

（2）let运算命令

1）给自变量加8

[root@codis-178 ~]# i=2
[root@codis-178 ~]# i=i+8
[root@codis-178 ~]# echo $i
i+8
[root@codis-178 ~]# unset i
[root@codis-178 ~]# i=2
[root@codis-178 ~]# let i=i+8
[root@codis-178 ~]# echo $i
10

2）监控Web服务状态，如果访问两次均失败，则报警

[root@codis-178 ~]# cat web.sh
#!/bin/bash
CheckUrl(){
	timeout=5
	fails=0
	success=0

	while true
		do
			wget --timeout=$timeout --tries=1 http://oldboy.blog.51cto.com -q -O /dev/null
			if [ $? -ne 0 ]
				then
					let fails=fails+1
			else
				let success+=1
			fi
			if [ $success -ge 1 ]
				then
					echo success
					exit 0
			fi
			if [ $fails -ge 2 ]
				then
					Critical="sys is down."
					echo $Critical|tee|mail -s "$Critical" tongxiaoda@anzhi.com
					exit 2
			fi
	done
}
CheckUrl
[root@codis-178 ~]# sh web.sh
success

（3）expr命令

1）expr用于计算

[root@codis-178 ~]# expr 2 + 2
4
[root@codis-178 ~]# expr 2 - 2
0
[root@codis-178 ~]# expr 2 * 2  # 需要转义
expr: syntax error
[root@codis-178 ~]# expr 2 \* 2
4
[root@codis-178 ~]# expr 2 / 2
1

2）expr配合变量计算

[root@codis-178 ~]# i=5
[root@codis-178 ~]# i=`expr $i + 6`
[root@codis-178 ~]# echo $i
11

3）判断一个变量或字符串是否为整数

[root@codis-178 ~]# i=5
[root@codis-178 ~]# expr $i + 6 &>/dev/null
[root@codis-178 ~]# echo $?
0
[root@codis-178 ~]# i=oldboy
[root@codis-178 ~]# expr $i + 6 &>/dev/null
[root@codis-178 ~]# echo $?
2

4）通过传参判断输出内容是否为整数

[root@codis-178 ~]# cat expr.sh
#!/bin/bash
expr $1 + 1 > /dev/null 2>&1
[ $? -eq 0 ] && echo int || echo chars
[root@codis-178 ~]# sh expr.sh oldboy
chars
[root@codis-178 ~]# sh expr.sh 119
int

5）通过read读入持续等待输入

[root@codis-178 ~]# cat judge_int.sh
#!/bin/bash
while true
do
	read -p "Pls input:" a
	expr $a + 0 >/dev/null 2>&1
	[ $? -eq 0 ] && echo int || echo chars
done
[root@codis-178 ~]# sh judge_int.sh
Pls input:oldgirl
chars
Pls input:76
int
Pls input:76sd
chars

6）通过expr判断文件扩展名是否符合要求

[root@codis-178 ~]# cat expr1.sh
#!/bin/bash
if expr "$1" : ".*\.pub" &>/dev/null
	then
		echo "you are using $1"
else
	echo "Pls use *.pub file"
fi
[root@codis-178 ~]# sh expr1.sh ttt.pub
you are using ttt.pub
[root@codis-178 ~]# sh expr1.sh ttt.py
Pls use *.pub file

7）使用expr命令实现ssh服务自带的ssh-copy-id公钥分发脚本

[root@codis-178 ~]# sed -n '10,20p' which /usr/bin/ssh-copy-id
sed: can't read which: No such file or directory
if [ "-i" = "$1" ]; then
  shift
  # check if we have 2 parameters left, if so the first is the new ID file
  if [ -n "$2" ]; then
    if expr "$1" : ".*\.pub" > /dev/null ; then
      ID_FILE="$1"
    else
      ID_FILE="$1.pub"
    fi
    shift         # and this should leave $1 as the target name
  fi

8）通过expr计算字符串长度

[root@codis-178 ~]# char="I am oldboy"
[root@codis-178 ~]# expr length "$char"
11
[root@codis-178 ~]# echo ${char}
I am oldboy
[root@codis-178 ~]# echo ${char}|wc -L
11
[root@codis-178 ~]# echo ${char}|awk '{print length($0)}'
11

9）请编写shell脚本，打印下面语句中字符数不大于6的单词

I am oldboy linux welcome to our training

[root@codis-178 ~]# cat word_length.sh
#!/bin/bash
for n in I am oldboy linux welcome to our training
do
	if [ `expr length $n` -le 6 ]
		then
			echo $n
	fi
done
[root@codis-178 ~]# sh word_length.sh
I
am
oldboy
linux
to
our

（4）bc命令

Linux内部计算器

[root@codis-178 ~]# bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
1+1
2
3*3
9

1）将bc用在命令行实现运算

[root@codis-178 ~]# echo 3+5|bc
8
[root@codis-178 ~]# echo 3.3+5.6|bc
8.9
[root@codis-178 ~]# echo 7.28-5.62|bc
1.66
[root@codis-178 ~]# echo "scale=2;355/113"|bc  # scale保留几位小数
3.14
[root@codis-178 ~]# echo "scale=4;355/113"|bc
3.1415
[root@codis-178 ~]# i=5
[root@codis-178 ~]# i=`echo $i+6|bc`
[root@codis-178 ~]# echo $i
11

2）通过一条命令计算输出1+2+3+...+10的表达式，并计算结果

[root@codis-178 ~]# echo `seq -s '+' 10`=`seq -s "+" 10|bc`
1+2+3+4+5+6+7+8+9+10=55
[root@codis-178 ~]# echo `seq -s '+' 10`=$((`seq -s "+" 10`))
1+2+3+4+5+6+7+8+9+10=55
[root@codis-178 ~]# echo `seq -s "+" 10`=`seq -s " + " 10|xargs expr`
1+2+3+4+5+6+7+8+9+10=55

（5）awk实现计算

[root@codis-178 ~]# echo "7.73 3.854" |awk '{print ($1-$2)}'
3.876
[root@codis-178 ~]# echo "367 131" |awk '{print ($1-3)/$2}'
2.77863

（6）$[]符号的运算

[root@codis-178 ~]# i=5
[root@codis-178 ~]# i=$[i+6]
[root@codis-178 ~]# echo $i
11
[root@codis-178 ~]# echo $[2*3]
6
[root@codis-178 ~]# echo $[3%5]
3

打印数学杨辉三角

[root@codis-178 ~]# cat shuxue.sh
#!/bin/bash
if (test -z $1);then
	read -p "Input Max Lines:" MAX
else
	MAX=$1
fi
i=1
while [ $i -le $MAX ]
do
	j=1
	while [ $j -le $i ]
	do
		f=$[i-1]
		g=$[j-1]
		if [ $j -eq $i ] || [ $j -eq 1 ];then
			declare SUM_${i}_$j=1
		else
			declare A=$[SUM_${f}_$j]
			declare B=$[SUM_${f}_$g]
			declare SUM_${i}_$j=`expr $A + $B`
		fi
		echo -en $[SUM_${i}_$j]" "
		let j++
	done
	echo
	let i++
done

[root@codis-178 ~]# sh shuxue.sh
Input Max Lines:4
1
1 1
1 2 1
1 3 3 1

2.基于Shell变量输入read命令的运算

（1）read命令

语法格式：read [参数] [变量名]

参数：

• -p prompt 设置提示信息
• -t timeout 设置输入等待时间，单位秒

[root@codis-178 ~]# read -t 10 -p "Pls input one num:" num
Pls input one num:18
[root@codis-178 ~]# echo $num
18
[root@codis-178 ~]# read -t 10 -p "Pls input two num:" a1 a2
Pls input two num:5 6
[root@codis-178 ~]# echo $a1
5
[root@codis-178 ~]# echo $a2
6

（2）以read命令读取及传参的综合案例

[root@codis-178 ~]# cat read_size01.sh
#!/bin/bash
read -t 15 -p "Please input two number:" a b

[ ${#a} -le 0 ] && {
	echo "the first num is null"
	exit 1
}
[ ${#b} -le 0 ] && {
	echo "the second num is null"
    exit 1
}

expr $a + 1 &>/dev/null
RETVAL_A=$?
expr $b + 1 &>/dev/null
RETVAL_B=$?
if [ $RETVAL_A -ne 0 -o $RETVAL_B -ne 0 ];then
	echo "one of the num is not num,pls input again."
	exit 1
fi

echo "a-b=$(($a-$b))"
echo "a+b=$(($a+$b))"
echo "a*b=$(($a*$b))"
echo "a/b=$(($a/$b))"
echo "a**b=$(($a**$b))"
echo "a%b=$(($a%$b))"
[root@codis-178 ~]# sh read_size01.sh
Please input two number:qq
the second num is null
[root@codis-178 ~]# sh read_size01.sh
Please input two number:12 6
a-b=6
a+b=18
a*b=72
a/b=2
a**b=2985984
a%b=0

通过传参方式

[root@codis-178 ~]# cat read_size02.sh
#!/bin/bash
a=$1
b=$2
Usage(){
	echo $"USAGE:sh $0 num1 num2"
	exit 1
}
if [ $# -ne 2 ];then
	Usage
fi
expr $a + 1 >/dev/null 2>&1
[ $? -ne 0 ] && Usage

echo "a-b=$(($a-$b))"
echo "a+b=$(($a+$b))"
echo "a*b=$(($a*$b))"
echo "a**b=$(($a**$b))"
if [ $b -eq 0 ]
	then
		echo "your input does not allow to run"
		echo "a/b =error"
		echo "a%b =error"
else
	echo "a/b =$(($a/$b))"
	echo "a%b =$(($a%$b))"
fi

[root@codis-178 ~]# sh read_size02.sh
USAGE:sh read_size02.sh num1 num2
[root@codis-178 ~]# sh read_size02.sh 7 old
USAGE:sh read_size02.sh num1 num2
[root@codis-178 ~]# sh read_size02.sh 7 3
a-b=4
a+b=10
a*b=21
a**b=343
a/b =2
a%b =1