Magento 2.1.18 is the final 2.1.x release. After June 2019, Magento 2.1.x will no longer receive security patches, quality fixes, or documentation updates.
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Add CLI commands

You module can optionally use Magento 2’s Symfony-based command-line interface (CLI) to provide commands for users to interact with. To use the CLI, see the following topics:

Command naming guidelines
How to add CLI commands

May 31st, 2019