Any missing versions within a description are not statements of unavailability. Though I am sure I used them, I simply do not remember testing these commands in other versions of Ubuntu, and would rather not list them if not one-hundred percent confident in their existence.
If there is an asterisk within the version, that command is most likely as universal a command as could exist.
Installed by default, and shows the current month. [v18.04]
There are quite a few nice options for cal, such as '-3' which shows the previous, current, and next month surrounding today. [v18.04]
Change the shell working directory. Recommend 'cd --help' to learn more options of cd. [v*,16.04,18.04]
Reports file system disk space usage. [v16.04,18.04]
Display amount of free and used memory in the system. [v18.04]
List directory contents. Highly recommend 'man ls' to learn more options of ls. [v*,16.04,18.04]
This will return the exact release version of Ubuntu Linux installed. [v16.04,18.04]
Print name of current/working directory. [v16.04,18.04]