Question

我正在尝试在UNIX中构建一个非常基本的4函数算术脚本，它不喜欢我的算术语句。我试图使用'bash arithmetic'语法

来自此来源

http://faculty.salina.k-state.edu/tim/unix_sg/bash/math.html

当您在UNIX中引用变量时，还需要使用“$”符号，以及何时不需要？

#!/bin/bash

str1="add"
str2="sub"
str3="div"
str4="mult"

((int3=0))
((int2=0))
((int1=0))


clear
read -p "please enter the first integer" $int1
clear
read -p "Please enter mathmatical operator'" input
clear
read -p "Please enter the second integer" $int2


if [ "$input" = "$str1" ];
then

((int3 = int1+int2))
   echo "$int3"


else

   echo "sadly, it does not work"

fi;

Answer 1

我认为这就是你想要的：

#!/bin/bash

str1="add"
str2="sub"
str3="div"
str4="mult"

((int3=0)) # maybe you can explain me in comments why you need a arithmetic expression here to perform an simple assignment?
((int2=0))
((int1=0))

echo -n "please enter the first integer > "
read int1
echo -n "Please enter mathmatical operator > "
read input
echo -n "Please enter the second integer > "
read int2


if [ $input = $str1 ]
then
((int3=int1 + int2))
   echo "$int3"
else
   echo "sadly, it does not work"
fi

exec $SHELL

您应该明确签出man bash。在那里记录了您需要指定$或不引用变量的命令。但除此之外：

var=123 # variable assignment. no spaces in between
echo $var # fetches/references the value of var. Or in other words $var gets substituted by it's value.

Answer 2

使用bc命令

类似这样的事情

echo "9/3+12" | bc

Answer 3

如果需要变量的值，请使用$。但是，read需要变量的名称：

read -p "..." int1

（从技术上讲，你可以做类似

的事情

name=int1
read -p "..." "$name"

设置int1的值，因为shell会将name扩展为字符串int1，然后read将其用作名称。）

Answer 4

这里过了一次：

op=( add sub div mult )

int1=0
int2=0
ans=0

clear
read -p "please enter the first integer > " int1
clear
IFS='/'
read -p "Please enter mathmatical operator (${op[*]})> " input
unset IFS
clear
read -p "Please enter the second integer > " int2

case "$input" in
    add)  (( ans = int1 + int2 ));;
    sub)  (( ans = int1 - int2 ));;
    div)  (( ans = int1 / int2 ));; # returns truncated value and might want to check int2 != 0
    mult) (( ans = int1 * int2 ));;
    *)   echo "Invalid choice"
           exit 1;;
esac

echo "Answer is: $ans"

您还需要检查用户是否输入数字：）

Answer 5

另一个

declare -A oper
oper=([add]='+' [sub]='-' [div]='/' [mul]='*')

read -r -p 'Num1? > ' num1
read -r -p "oper? (${!oper[*]}) > " op
read -r -p 'Num2? > ' num2

[[ -n "${oper[$op]}" ]] || { echo "Err: unknown operation $op" >&2 ; exit 1; }
res=$(bc -l <<< "$num1 ${oper[$op]} $num2")
echo "$num1 ${oper[$op]} $num2 = $res"

如何在UNIX中执行算术？

5 个答案: