Create Interactive Menus in Bash

Summary:
Use select and loops to build CLI menus.

Command-line menus can greatly enhance the usability and interactivity of Bash scripts. Whether you're building utilities or just want to provide friendly script options, interactive menus using Bash's select and loops can help. In this post, we’ll explore how to create clear, intuitive CLI menus and guide users through choices step by step.

Why Menus in Bash?

Bash scripts often require user input. Rather than re-typing answers to prompts or remembering command options, menus provide an efficient, error-reducing interface. They’re especially useful for:

System administration scripts
Installation assistants
Automation tools for teams
Learning and demo environments

1. The `select` Statement

Bash’s select command is a built-in way to present numbered options. It's simple and powerful.

Syntax:

select VARIABLE in OPTIONS; do
    # actions
done

VARIABLE is set to the chosen option’s value.
The loop continues until you break it.

Example:

#!/bin/bash

echo "Choose your favorite fruit:"

select fruit in Apple Banana Orange Quit
do
    case $fruit in
        Apple|Banana|Orange)
            echo "You selected: $fruit"
            break
            ;;
        Quit)
            echo "Goodbye!"
            break
            ;;
        *)
            echo "Invalid option."
            ;;
    esac
done

How it works:
On running, Bash presents:

1) Apple
2) Banana
3) Orange
4) Quit
#?

When the user enters a number, $fruit gets the corresponding value.

2. Custom Menus with Loops

select is great, but sometimes you want finer control—for validation, non-numbered prompts, complicated workflows, or non-list menus.

Example: Menu Loop

#!/bin/bash

while true; do
    echo "MAIN MENU:"
    echo "1) Show disk usage"
    echo "2) Show memory usage"
    echo "3) Quit"
    read -p "Enter your choice [1-3]: " choice

    case $choice in
        1) df -h ;;
        2) free -m ;;
        3) echo "Exiting." ; break ;;
        *) echo "Invalid option." ;;
    esac
    echo ""
done

Features:

Input is validated.
Each option triggers a command.
Menu loops until “Quit” is selected.

3. Making Menus User-Friendly

Here are a few tips for effective Bash menus:

a. Add Input Validation

Use patterns and conditions to catch errors and guide users.

if [[ ! $choice =~ ^[1-3]$ ]]; then
    echo "Please enter a valid number (1, 2, or 3)."
fi

b. Clear the Screen

Make repeated menus cleaner:

clear

c. Use Functions for Actions

Structure actions as functions for clarity and reusability.

show_disk() {
    df -h
}

show_mem() {
    free -m
}

4. Combining `select` and Loops

They’re not mutually exclusive! Sometimes you want selection and advanced handling:

while true; do
    echo "Choose an action:"
    select action in List_Files Show_Date Quit; do
        case $action in
            List_Files)
                ls
                break
                ;;
            Show_Date)
                date
                break
                ;;
            Quit)
                exit 0
                ;;
            *)
                echo "Invalid option."
                ;;
        esac
    done
    echo
done

5. A Practical Example: System Info Menu

Here’s a complete, ready-to-use system info menu script:

#!/bin/bash

while true; do
    clear
    echo "===== SYSTEM INFO MENU ====="
    echo "1) Show disk usage"
    echo "2) Show memory usage"
    echo "3) Show logged-in users"
    echo "4) Show running processes"
    echo "5) Quit"
    read -p "Choose an option [1-5]: " opt

    case "$opt" in
        1) echo; df -h ; read -p "Press Enter to continue...";;
        2) echo; free -m ; read -p "Press Enter to continue...";;
        3) echo; who ; read -p "Press Enter to continue...";;
        4) echo; ps aux | less ;;
        5) echo "Goodbye!"; break ;;
        *) echo "Invalid option!"; sleep 1 ;;
    esac
done

Conclusion

With Bash's select command and flexible use of loops, you can build interactive CLI menus in minutes. Menus make scripts friendlier, reduce user error, and offer a professional touch. Try adding a menu to your next Bash project!

Further Resources

Happy scripting!