使用读取和函数计算面积

使用读取和函数计算面积

我打算计算圆的面积。

#! /usr/local/bin/bash
read -p "Enter a radius: " 
area () {
    a=$(( 3 * $REPLY * 2 ))
    return $a
}
echo $(area)

运行但不返回任何内容

$ bash area.sh
Enter a radius: 9

然后通过引用来重构它

#! /usr/local/bin/bash
read -p "Enter a radius: "  radius
area (radius) {
    a=$(( 3 * $radius * 2 ))
    return "$a"
}
echo "$(area)"

它仍然不能正常工作。

bash area.sh
Enter a radius: 9
area.sh: line 3: syntax error near unexpected token `radius'
area.sh: line 3: `area (radius) {'

如何做这样的计算?

答案1

这是一个快速脚本,它接受半径的输入,然后将其提供给函数,area()然后回显返回值。这适用于bc已安装的二进制计算器。

#!/bin/bash
function area(){
    circ=$(echo "3.14 * $1^2" | bc)
}

#Read in radius
read -p "Enter a radius: "

#Send REPLY to function
area $REPLY

#Print output
echo "Area of a circle is $circ"

例子:

terrance@terrance-ubuntu:~$ ./circ.bsh 
Enter a radius: 6
Area of a circle is 113.04

或者我稍微扩展了一下脚本,以显示更多从命令行或脚本本身读取变量的内容:

#!/bin/bash
function area(){
    areacirc=$(printf "3.14 * $1^2\n" | bc)
    diamcirc=$(printf "2 * $1\n" | bc)
    circcirc=$(printf "2 * 3.14 * $1\n" | bc)
}

#Read in radius from command line or from read
if [[ $1 == "" ]]; then
    read -p "Enter a radius: "
else
    printf "Radius of a cirle is $1\n"
    REPLY=$1
fi

#Send REPLY to area function
area $REPLY

#Print output from variables set by area function
printf "Diameter of a circle is $diamcirc\n"
printf "Circumference of a circle is $circcirc\n"
printf "Area of a circle is $areacirc\n"

例子:

terrance@terrance-ubuntu:~$ ./area.bsh 6
Radius of a cirle is 6
Diameter of a circle is 12
Circumference of a circle is 37.68
Area of a circle is 113.04

或者

terrance@terrance-ubuntu:~$ ./area.bsh
Enter a radius: 13
Diameter of a circle is 26
Circumference of a circle is 81.64
Area of a circle is 530.66

答案2

Bash 中的函数没有命名参数。您不能执行以下操作:

area (foo) { ...
function area (foo) { ...

你可以做:

area () {
    local radius a   # set a local variable that does not leak outside the function
    radius=$1   # Save the first parameter to local variable
    a=$(( 3 * radius * 2 ))
    echo "$a"
}

进而:

echo "$(area "$REPLY")"  # use $REPLY as the first argument

因为return设置了函数的退出状态,而$(area)使用函数的输出。它们是不同的。

另外,虽然 bash 不支持浮点运算,但它支持指数运算:

$ bash -c 'echo $((3 * 3 ** 2))'
27

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