Add an Interactive Prompt to a Drush Command for Drupal 8, 9, 10, and 11

When the logic of a command depends on user input, it's useful to set up an interactive questionnaire inside the command code. This allows you to provide the user with more context about the input they're providing, and ensure that you collect all the necessary values. This is especially useful when the command uses a pre-defined list of options and the values require memorization. An example of this is the drush cache-clear command that comes with Drush core. It requires an argument indicating which cache to clear, which you can specify at the command line; however, if you invoke the command with no arguments it will present you with a list of cache bins to choose from and a UI for selecting one.

Drush 9+ can access the Input/Output (I/O) object via the $this->io() method. This object -- an instance of \Drush\Style\DrushStyle -- holds information about user-provided input, and utilities for manipulating that input. To ask a user a question, use an io() object in the command callback method. It can take over the execution flow of the command as needed to stop and gather additional input. The I/O system has various methods for asking confirmation or choice questions such as confirm() and select().

In addition to prompting for input, the I/O object can be used to provide other styling to the command, like progress bars.

In this tutorial we'll:

• Learn how to prompt the user for additional input
• Process the user's answer as part of the command execution flow

By the end of this tutorial you should understand how to prompt a user for additional input for a custom Drush command.