Dynamic menu with select statement in Bash

Whenever I need to whip up a quick command line tool, my go-to is usually Python. Python’s CLI solutions tend to be more robust than their Shell counterparts. However, dealing with its portability can sometimes be a hassle, especially when all you want is to distribute a simple script. That’s why while toying around with argparse to create a dynamic menu, I decided to ask ChatGPT if there’s a way to achieve the same using native shell scripting. Delightfully, it introduced me to the dead-simple select command that I probably should’ve known about years ago. But I guess better late than never! Here’s what I was trying to accomplish:

Print a menu that allows a user to choose an option and then trigger a specific function associated with the chosen option. When you run the script, it should present you with something similar to this:

1) Option 1
2) Option 2
3) Option 3
4) Quit
Please enter your choice: 1
You selected Option 1.
Please enter your choice: 2
You selected Option 2.
Please enter your choice: 3
You selected Option 3.
Please enter your choice: 4

Whenever the user selects an option, the script dispatches an associated function with the option. Currently, the associated function just prints You selected option x but it has the freedom to do whatever it wants. The following native Shell script uses select to produce the output above:

#!/usr/bin/env bash
# script.sh

# Define an array of menu options
options=("Option 1" "Option 2" "Option 3" "Quit")

# Function to handle Option 1
function option1 {
    echo "You selected Option 1."
    # Add your Option 1 code here
}

# Function to handle Option 2
function option2 {
    echo "You selected Option 2."
    # Add your Option 2 code here
}

# Function to handle Option 3
function option3 {
    echo "You selected Option 3."
    # Add your Option 3 code here
}

# Display the menu and process user selection
PS3="Please enter your choice: "
select option in "${options[@]}"; do
    case $option in
        "Option 1")
            option1
            ;;
        "Option 2")
            option2
            ;;
        "Option 3")
            option3
            ;;
        "Quit")
            break
            ;;
        *)
            echo "Invalid option. Try again."
            ;;
    esac
done

The snippet allows users to make selections from a list of options. It starts by defining an array called options which holds the available possibilities. Each option corresponds to a specific function, such as option1, option2, and option3 which can be customized to perform specific actions or tasks.

The script then prompts the user to enter their choice using the select statement. The user’s selection is stored in the variable option. Then it uses a case statement to match the selected option and execute the corresponding function. For example, if the user chooses Option 1 by typing 1 into the console, the script calls the option1 function and displays a message confirming the selection. The same applies to Option 2 and Option 3. If the user selects Quit by typing 4, the script breaks out of the loop and terminates. Moreover, if the user enters an invalid option, the script displays an error message indicating that the option is not recognized and prompts the user to try again.

Here’s a little more useful script to run some common Docker commands based on the user’s selection. The script assumes that Docker engine is installed on the targeted system:

#!/usr/bin/env bash

# Define an array of menu options
options=(
"Show Docker Images"
"Remove Docker Image"
"Show Docker Containers"
"Remove Docker Container"
"Stop All Containers"
"Reprint Options"
"Quit"
)

# Function to show all Docker images
function show_docker_images {
    echo "Listing Docker images:"
    docker images
}

# Function to remove a Docker image
function remove_docker_image {
    read -p "Enter the image ID or name to remove: " image_id
    echo "Removing Docker image: $image_id"
    docker rmi "$image_id"
}

# Function to show all Docker containers
function show_docker_containers {
    echo "Listing Docker containers:"
    docker ps -a
}

# Function to remove a Docker container
function remove_docker_container {
    read -p "Enter the container ID or name to remove: " container_id
    echo "Removing Docker container: $container_id"
    docker rm "$container_id"
}

# Function to stop all Docker containers
function stop_all_containers {
    echo "Stopping all Docker containers:"
    docker stop $(docker ps -aq)
}

# Function to reprint the options
function reprint_options {
    echo "Available Options:"
    for index in "${!options[@]}"; do
        echo "$((index+1))) ${options[index]}"
    done
}

# Display the menu and process user selection
PS3="Please enter your choice: "
select option in "${options[@]}"; do
    case $option in
        "Show Docker Images")
            show_docker_images
            ;;
        "Remove Docker Image")
            remove_docker_image
            ;;
        "Show Docker Containers")
            show_docker_containers
            ;;
        "Remove Docker Container")
            remove_docker_container
            ;;
        "Stop All Containers")
            stop_all_containers
            ;;
        "Reprint Options")
            reprint_options
            ;;
        "Quit")
            break
            ;;
        *)
            echo "Invalid option. Try again."
            ;;
    esac
done

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