Using functions in menus

In Chapter 6, Iterating with Loops, we created the menu.sh file. Menus are great targets to use functions, as the case statement is maintained very simply with single-line entries, while the complexity can still be stored in each function. We should consider creating a function for each menu item. If we copy the previous $HOME/bin/menu.sh to $HOME/bin/menu2.sh, we can improve the functionality. The new menu should look like the following code:

#!/bin/bash 
# Author: @likegeeks 
# Web: likegeeks.com 
# Sample menu with functions 
# Last Edited: April 2018 
 
to_lower() { 
    input="$1" 
    output=$( echo $input | tr [A-Z] [a-z]) 
return $output 
} 
 
do_backup() { 
    tar -czvf $HOME/backup.tgz ${HOME}/bin 
} 
 
show_cal() { 
    if [ -x /usr/bin/ncal ] ; then 
      command="/usr/bin/ncal -w" 
    else 
      command="/usr/bin/cal" 
    fi 
    $command 
} 
 
while true 
do 
  clear 
  echo "Choose an item: a, b or c" 
  echo "a: Backup" 
  echo "b: Display Calendar...