On a clean install of 10.14.5: Multiple reports of the beta version not working using a headless install: https://github.com/Homebrew/install/issues/206
This lead me to trying to manually do a headless install. I tried all of the various methods in How can I install the Command Line Tools completely from the command line? and none of them show anything but:
Mac-mini:~ anka$ /usr/sbin/softwareupdate -l | grep "\*"
* MacBook Pro Supplemental Update-
Yet, I can xcode-select --install and it allows me to install it.
Anyone know how to get it to show up in softwareupdate -l so we can headless install it?