I know I'll sound like I am an old man yelling "Get off my lawn!", but as far as I can tell this is a text-mode application but it is not a commandline interface. Note that it's only the HN submission title that gets it wrong, the Readme.md on GitHub correctly calls it "terminal-based" rather than CLI.
An actual commandline interface would also be cool, to be able to easily send iMessages from shell scripts, for example.
Sure, you're right, I just got excited typing out the title :) You could actually use the AppleScript files in the repo to send messages directly without the use of the rest of the code. Usage would be like this:
osascript sendmessage_single.AppleScript PHONE_NUMBER_OR_ICLOUD_EMAIL "my message text" false false
An actual commandline interface would also be cool, to be able to easily send iMessages from shell scripts, for example.