Shell:变量数值计算(上) 算数运算符{mtitle title="Shell常见的算数运算符"/}算数运算符意义+、-加法(正号)、减法(负号)*、/、%乘、除、取余**幂运算++、--增加及减少!、&&、双竖线逻辑非(取反)、逻辑与、逻辑或<、<=、>、=>比较符号(小于、小于等于、大于、大于等于)==、!=、=比较符号(等于、不相等、对于字符串“=”也可以表示等于)<<、>>向左移，向右移~、单竖线、&、^按位取反、按位异或、按位与、按位或=、+=、-=、*=、/=、%=赋值运算符{mtitle title="Shell中常见的算数运算命令"/}运算符与运算命令意义(())用于整数运算的常用命令let用于整数运算，类似于(())expr可用于整数运算bcLinux中的一个计算器程序（适合整数和小数运算）$[]用于整数运算awkawk既可以整数运算，也可以小数运算declare定义变量值和属性，-i参数可以用于定义整形变量，做运算(())运算用法root@cs:/server/scripts# echo $((8+2)) 10 root@cs:/server/scripts# echo $((8-2)) 6 root@cs:/server/scripts# echo $((8*2)) 16 root@cs:/server/scripts# echo $((8/2)) 4 root@cs:/server/scripts# echo $((8%2)) 0 root@cs:/server/scripts# echo $((8**2)) 64 root@cs:/server/scripts# ((i=6)) root@cs:/server/scripts# ((i=i*2)) root@cs:/server/scripts# echo $i 12 root@cs:/server/scripts# a=$((100*(100+1)/2)) root@cs:/server/scripts# echo $a 5050 root@cs:/server/scripts# echo $((100*(100+1)/2)) 5050 root@cs:/server/scripts# echo $((3<8)) 1 #1表示为真 root@cs:/server/scripts# echo $((1>8)) 0 #0表示为假{message type="warning"}PS:上面的数字及变量必须为整数，不能用小数和字符串{/message}(())运算的Shell脚本示例root@cs:/server/scripts# cat test.sh #!/bin/bash a=6 b=12 echo "a+b=$(($a+$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%$b))" echo "a++:$((a++))" echo "a=$a" echo "++a:$((++a))" echo "a=$a" echo "b--:$((--b))" echo "b=$b" echo "--b:$((--b))" echo "b=$b"其执行结果root@cs:/server/scripts# sh test.sh a+b=18 a-b=-6 a*b=72 a/b=0 a**b=2176782336 a%b=6 a++:6 a=7 ++a:8 a=8 b--:11 b=11 --b:10 b=10通过命令行传参方式，实现混合运算root@cs:/server/scripts# cat test1.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%$b))" echo "a++:$((a++))" echo "a=$a" echo "++a:$((++a))" echo "a=$a" echo "b--:$((--b))" echo "b=$b" echo "--b:$((--b))" echo "b=$b"其执行结果root@cs:/server/scripts# sh test1.sh 8 4 a+b=12 a-b=4 a*b=32 a/b=2 a**b=4096 a%b=0 a++:8 a=9 ++a:10 a=10 b--:3 b=3 --b:2 b=2实现输入两个数进行加减乘除的计算器利用read命令读入功能root@cs:/server/scripts# cat jsq.sh #!/bin/bash print_usage(){ print "please enter an integer\n" exit 1 } read -p "Please input first number:" a if [ -n "`echo $a|set 's/[0-9]//g'`" ];then print_usage fi read -p "Please input first operators:" b if [ "${b}" != "+" ]&&[ "${b}" != "-" ]&&[ "${b}" != "*" ]&&[ "${b}" != "/" ];then print_usage exit 2 fi read -p "Please input first number:" c if [ -n "`echo $c|set 's/[0-9]//g'`" ];then print_usage fi echo "${a}${b}${c}=$((${a}${b}${c}))" 其输入结果为 root@cs:/server/scripts# sh jsq.sh Please input first number:6 Please input first operators:+ Please input first number:4 6+4=10 root@cs:/server/scripts# sh jsq.sh Please input first number:8 Please input first operators:- Please input first number:4 8-4=4利用命令行传参方式root@cs:/server/scripts# sh jsq1.sh 8 + 5 8+5=13 root@cs:/server/scripts# sh jsq1.sh 8 - 5 8-5=3 root@cs:/server/scripts# sh jsq1.sh 8 \* 5 #*号要转义 8*5=40 root@cs:/server/scripts# sh jsq1.sh 8 / 5 8/5=1let 运算用法root@cs:/server/scripts# i=8 root@cs:/server/scripts# i=i+8 root@cs:/server/scripts# echo $i i+8 root@cs:/server/scripts# unset i root@cs:/server/scripts# i=8 root@cs:/server/scripts# let i=i+8 root@cs:/server/scripts# echo $i 16提示：let i=i+8等同于 ((i=i+8)),不过后者效率高一些{mtitle title="示例"/}root@cs:/server/scripts# cat 04_03_test.sh #!/bin/bash CheckUrl(){ #定义一个函数 timeout=5 #定义wget访问的超出时间 fails=0 #初始化访问网站失败的次数记录变量，若失败达到两次，报警 success=0 #初始化访问网站成功的次数记录变量，如果为1 则表示成功，退出 while true #持续循环检测 do wget --timeout=$timeout --tries=1 https://www.xiaobai666.top -q -O /dev/null #wget访问测试 if [ $? -ne 0 ] #如果上述wget不成功，即返回值不为零，执行if语句 then let fails=fails+1 #失败加1 else let success+=1 #成功加1 fi if [ $success -ge 1 ] #如果成功次数大于等于1 then echo success exit 0 fi if [ $fails -ge 2 ] #如果失败的次数大于等于2 then Critical="sys is down." echo "$Critical|tee|mail -s $Critical" #3285884651@qq.com exit 2 fi done } CheckUrl执行结果root@cs:/server/scripts# sh 04_03_test.sh success root@cs:/server/scripts# sh -x 04_03_test.sh + CheckUrl + timeout=5 + fails=0 + success=0 + true + wget --timeout=5 --tries=1 https://www.xiaobai666.top -q -O /dev/null + '[' 0 -ne 0 ']' + let success+=1 + '[' 1 -ge 1 ']' + echo success success + exit 0expr命令用法root@cs:/server/scripts# expr 2 + 2 4 root@cs:/server/scripts# expr 2 - 2 0 root@cs:/server/scripts# expr 2 \* 2 4 root@cs:/server/scripts# expr 2 / 2 1expr配合变量计算root@cs:/server/scripts# i=5 root@cs:/server/scripts# i=$(expr $i + 6) root@cs:/server/scripts# echo $i 11 root@cs:/server/scripts# i=`expr $i + 6` root@cs:/server/scripts# echo $i 17{message type="warning"}PS:expr $i +6=$(expr $i + 6)，不能用小数和字符串{/message}通过expr判断变量或者数字是否为整数root@cs:/server/scripts# i=8 root@cs:/server/scripts# expr $i + 6 &>/dev/null root@cs:/server/scripts# echo $? 0 root@cs:/server/scripts# i=skfhs root@cs:/server/scripts# expr $i + 6 &>/dev/null root@cs:/server/scripts# echo $? 2也可以通过echo $? 判断上个命令是否运行成功通过read 读入持续等待例子cat expr.sh #!/bin/bash while true do read -p "Please input:" num expr $num + 0 >/dev/null 2>&1 [ $? -eq 0 ]&& echo int || echo chars done 执行结果 root@cs:/server/scripts# sh expr.sh Please input:123 int Please input:ersfs chars Please input:hf chars Please input:456456 int将前文的混合运算，判断传参的个数及通过expr判断传入的参数是否为整数root@cs:/server/scripts# cat test2-2.sh #!=/bin/bash print_usage(){ echo "please input two number:" exit 1 } [ $# -ne 2 ] && { echo $"USAGE $0 NUM1 NUM2" exit 1 } a=$1 b=$2 expr $a + 1 >/dev/null RETVAL_A=$? expr $b + 1 >/dev/null RETVAL_B=$? if [ $RETVAL_A -ne 0 -o $RETVAL_B -ne 0 ] then echo "Please input two num" exit 2 fi echo "a+b=$(($a+$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%$b))" echo "a++:$((a++))" echo "a=$a" echo "++a:$((++a))" echo "a=$a" echo "b--:$((--b))" echo "b=$b" echo "--b:$((--b))" echo "b=$b"执行结果root@cs:/server/scripts# sh test2-2.sh 6 3 a+b=9 a-b=3 a*b=18 a/b=2 a**b=216 a%b=0 a++:6 a=7 ++a:8 a=8 b--:2 b=2 --b:1 b=1通过espr计算字符串的长度root@cs:/server/scripts# char="are you ok" root@cs:/server/scripts# expr length "$char" 10 root@cs:/server/scripts# echo ${#char} 10 root@cs:/server/scripts# echo ${char}|awk '{print length($0)}' 10 root@cs:/server/scripts# echo ${char}|wc -L 10找出字符数不大于5的单词root@cs:/server/scripts# cat test2-3.sh #!/bin/bash for i in dhf gsh df adfs asdjkja do if [ `expr length $i` -le 5 ] then echo $i fi done执行结果root@cs:/server/scripts# sh test2-3.sh dhf gsh df adfs