Bdtyktl

I intend to calculate area of a circle.

#! /usr/local/bin/bash

read -p "Enter a radius: " 

area () {

    a=$(( 3 * $REPLY * 2 ))

    return $a

}

echo $(area)

Run but return nothing

$ bash area.sh

Enter a radius: 9

Then to refactor it by quoting

#! /usr/local/bin/bash

read -p "Enter a radius: "  radius

area (radius) {

    a=$(( 3 * $radius * 2 ))

    return "$a"

}

echo "$(area)"

It still not work properly.

bash area.sh

Enter a radius: 9

area.sh: line 3: syntax error near unexpected token `radius'

area.sh: line 3: `area (radius) {'

How to do such a calculation?

Functions in bash do not have named parameters. You cannot do:

area (foo) { ...

function area (foo) { ...

You can do:

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"

}

And then:

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

Since return sets the exit status of the function, whereas $(area) uses the output of the function. These are different.

Also, while bash does not support floating-point arithmetic, it does support exponentiation:

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

27

This is a quick script taking the input of the radius then feeding it to the function of area() then echoing out the return value. This works with bc or binary calculator installed.

#!/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"

Example:

terrance@terrance-ubuntu:~$ ./circ.bsh 

Enter a radius: 6

Area of a circle is 113.04

Or I have expanded on the script a little to show more of reading in a variable either from the command line or from the script itself:

#!/bin/bash

function area(){

    areacirc=$(printf "3.14 * $1^2n" | bc)

    diamcirc=$(printf "2 * $1n" | bc)

    circcirc=$(printf "2 * 3.14 * $1n" | 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 $1n"

    REPLY=$1

fi



#Send REPLY to area function

area $REPLY



#Print output from variables set by area function

printf "Diameter of a circle is $diamcircn"

printf "Circumference of a circle is $circcircn"

printf "Area of a circle is $areacircn"

Example:

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

or

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