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The eval statement is used to send results form the function to the calling program

The main program is named program.using.function.sh

#! /bin/bash
 
# Declare the function library file
. /home/user/libprogram.using.function.sh
 
# Variables 
number1=7
number2=8
number3=9
number4=10
result=""
other=""
calculation=""
 
# Calling the function. Sending 4 and receiving 3 variables
testfunction $number1 $number2 $number3 $number4 result other calculation
echo returnvalue: $?
echo -e "$result\n$other\n$calculation"

The library file with the function is called libprogram.using.function.sh

#! /bin/bash
 
function testfunction()
{
  # Letting the user know that this is the function
  echo Start function
 
  # Variables
  # Input variables
  local fn_number1=$1 
  local fn_number2=$2 
  local fn_number3=$3 
  local fn_number4=$4 
  # Variables for the results
  local fn_result1=$5
  local fn_result2=$6
  local fn_result3=$7
 
  # Display the contents of the variables
  echo $1 $2 $3 $4 $5 $6 $7
 
  # Variables of which the value will be returned by the function with a value given
  local fn_variable1='Tekst 145'
  local fn_variable2='An other text with number 169'
  local fn_calculation=$(( $fn_number1 * $fn_number2 * $fn_number3 * $fn_number4 ))
  # Show the contents of these variables
  echo fn_variable 2x: $fn_variable1 $fn_variable2
  echo Result of calculation: $fn_calculation
 
  # Set the return values
  eval $fn_result1="'$fn_variable1'"
  eval $fn_result2="'$fn_variable2'"
  eval $fn_result3="'$fn_calculation'"
 
  # Display the return values
  echo fn_result 3x: $fn_result1 $fn_result2 $fn_result3
 
  # Show that the function is ready, finished
  echo finish function
 
  # Return the exit code (a number between 0 and 256). Here we choose 27
  return 27
}

Note that the values used in the eval commands have to be a variable. So eval $fn_result4=“'Hello'“ does not work

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