How to print current username in Crystal-lang?

Yes this is still somewhat missing in the standard library. There's an ongoing discussion about it here: https://github.com/crystal-lang/crystal/issues/7829

Meanwhile we can quickly bind getuid(2) or geteuid(2) ourselves and combine it with System::User:

require "system/user"

lib LibC
  fun getuid : UidT
end

user = System::User.find_by id: LibC.getuid.to_s

pp user.username

https://carc.in/#/r/b63s