Somehow I made it this far without actually understanding how sudo works. For years, I’ve just typed sudo, typed my password, and revelled in my new, magical, root super powers. The other day and I finally looked into it – to be honest, the mechanism is not at all what I expected. After going through the basics, we’ll walk through creating our own version of sudo. How Sudo Works sudo is just a regular old program that essentially does 3 things:

Many software engineers use database indexes every day, but few of us really understand how they work. In this post I’ll explain: How indexing works in Postgres using B-Trees What B-Trees are Why they are a good fit for this problem Indexes in Postgres Postgres actually offers 4 different kinds of indexes for different use cases. In this post I’ll be focusing on the “normal” index, the kind you get by default when you run create index.

I always wondered how Google Authenticator style 2-factor codes worked. The process of going from QR code to rotating 6-digit pin seemed a bit magical. A few days ago, my curiosity found itself coupled with some free time. Here’s what I found: What’s in the QR Code I scanned the QR code from Github with a barcode scanning app. Here’s what’s inside: otpauth://totp/Github:rcoh?secret=onswg4tforrw6zdf&issuer=Github Not too surprising. It tells us the protocol, TOTP, who is issuing this OTP code (Github), and most importantly the secret:1

The code for this post, as well as the post itself, are on github. This post is part 3 of a 3 part series. Part 1: Parsing Part 2: Generate an NFA Part 3: Evaluate an NFA Evaluating the NFA NFAs, DFAs and Regular Expressions Recall from part 2 that there are two types of finite automata: deterministic and non-deterministic. They have one key difference: A non-deterministic finite automata can have multiple paths out of the same node for the same token as well as paths that can be pursued without consuming input.

The code for this post, as well as the post itself, are on github. This post is part 2 of a 3 part series. Part 1: Parsing Part 2: Generate an NFA Part 3: Evaluate an NFA Converting the Parse Tree to an NFA In the last post, we transformed the flat string representation of a regular expression to the hierarchical parse tree form. In this post we’ll transform the parse tree to a state machine.

The code for this post, as well as the post itself, are on github. This post is part 1 of a 3 part series. Part 1: Parsing Part 2: Generate an NFA Part 3: Evaluate an NFA Until recently, regular expressions seemed magical to me. I never understood how you could determine if a string matched a given regular expression. Now I know! Here’s how I implemented a basic regular expression engine in under 200 lines of code.