Shellvarnia: Shell Variables Down Unix

Political map showing Shellvarnia on the left side of the continent, Flapjackia, separated from Userland (on the east coast of Flapjackia) by Environmentopia in the middle. No direct connection between Shellvarnia and Userland is shown.

Political map of continent, Flapjackia, showing countries of Shellvarnia, Environmentopia, and Userland.

This is a fun short story about the fictional land of Shellvarnia, located Down Unix, that occurred to me one night while I was reading Brian Ward‘s excellent book, How Linux Works: What Every Superuser Should Know. Mixing one dash of political satire with a heaping serving of Unix lore, it will entertain and inform novices approaching a Linux VM for the first time.  If you’ve ever wondered about distinctions between local shell variables and environment variables, /bin/sh from /bin/csh, and who built that wall between Shellvarnia and Environmentopia, then this story was written just for you.  Continue reading

Birthday Paradox

M.C Escher inspired birthday balloons overlapping each other paradoxically. Watercolor illustration by Allen West.

M.C. Escher inspired birthday balloon paradox watercolor by Allen West.

A math magician appears before you on the street in a puff of smoke, and he will make you his apprentice if you can but answer one question. You fantasize how you could make your investment portfolio grow if only you knew magic, or how you could star in your own series of blockbuster films–move aside Harry Potter! But before you get carried away, the magician posits his question to you: how many people off of the street do I need to invite to my magic show to have a 50% chance that any two of them celebrate their birthday on the same day? You sweat a little, think a little, then sweat a little more before answering: 183.

You won’t be attending Hogwarts anytime soon, my friend. You’ve been hit by, you’ve been struck by, a Birthday Paradox! Continue reading