Using functions in Bash

Question

Is this the correct syntax for parameterized functions?

#!/bin/bash

twoPow()
{
    prod=1
    for((i=0;i<$1;i++));
    do
        prod=$prod*2
    done
    return prod
}

echo "Enter a number"
read num
echo `twoPow $num`

Output:

bash sample.sh

Enter a number

3

sample.sh: line 10: return: prod: numeric argument required

Part 2:

I removed the return, but what should I do if I want to run multiple times and store results like below? How can I make this work?

#!/bin/bash

tp1=1
tp2=1

twoPow()
{
    for((i=0;i<$1;i++));
    do
        $2=$(($prod*2))
    done
}

twoPow 3 tp1
twoPow 2 tp2
echo $tp1+$tp2

change return prod to echo $prod and re-try. ref: stackoverflow.com/questions/8742783/… — A Lan
– A Lan, Commented Oct 9, 2013 at 3:10

Peter Mortensen · Accepted Answer · 2021-03-15 23:14:07Z

4

In Bash scripts you can't return values to the calling code.

The simplest way to emulate "returning" a value as you would in other languages is to set a global variable to the intended result.

Fortunately in bash all variables are global by default. Just try outputting the value of prod after calling that function.

edited Mar 15, 2021 at 23:14

Peter Mortensen

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answered Oct 9, 2013 at 3:04

Govind Parmar

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2 Comments

codepk Over a year ago

This works:

#!/bin/bash  prod=1  twoPow() { 	for((i=0;i<$1;i++));  	do 		prod=$(($prod*2)) 	done }  echo "Enter a number" read num twoPow $num echo $prod

codepk Over a year ago

What should I do if I want to call it multiple times and store result?

Peter Mortensen · Accepted Answer · 2021-03-15 23:16:17Z

0

A sample Bash function definition and call with a few parameters and return values. It may be useful and it works.

#!/bin/sh

## Define function
function sum()
{

 val1=$1

 val2=$2

 val3=`expr $val1 + $val2`

 echo $val3

}

# Call function with two parameters and it returns one parameter.
ret_val=$(sum 10 20)
echo $ret_val

edited Mar 15, 2021 at 23:16

Peter Mortensen

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answered Oct 9, 2013 at 3:25

Mandar Pande

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1 Comment

chepner Over a year ago

expr is not needed for arithmetic anymore; use val3=$(( val1 + val2 )) instead.

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