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" 
  echo "c: Exit" 
  read -sn1 
  REPLY=$(to_lower "$REPLY") 
  case "$REPLY" in 
    a) do_backup;; 
    b) show_cal;; 
    c) exit 0;; 
  esac 
  read -n1 -p "Press any key to continue" 
done 

As we can see, we still maintain the simplicity of the case statement; however, we can develop the script to add in more complexity through the functions. For example, when choosing option b for the calendar, we now check to see whether the ncal command is available. If it is, we use ncal and use the -w option to print the week number. We can see this in the following screenshot, where we have chosen to display the calendar and install ncal:

We can also not be concerned about the Caps Lock key as the to_lower function converts our selection to lowercase. Over time, it would be very easy to add additional elements to the functions, knowing that we only affect that single function.