Regular expression as Finite-state machine - Short

Key Takeaways

a regular expression is a pattern that can match a string of characters for example ABC would first look for an A then a B and then a C you could also draw this pattern as a finite state automaton or a finite state machine this is the kind of theoretical stuff you learn in computer science so we start here then we can move to the next state when we see an A to the next one we see a B in to the last one when we see a C which means we match the string and obviously if our string would have been ax C instead then we would find the a and move forward but there is no path for the X so our pattern doesn't match the string ax C and if you think about these reg exists as these graphs all the other features of reg X become very clear so it's really helpful to draw this if you find a more complex reg X you don't understand or if you want to come up with the regs yourself maybe start drawing a finite state machine instead and then translate it into the text version there's this really awesome website called debug X which basically does exactly that for you and I use it all the time because reg eggs are often used to validate input and it can be really helpful to see if you can somehow get malicious input through here's just an example a simple male reg X and while you type you can observe here the pink cursor that shows you what characters you are allowed to use next until it matches and if it doesn't match you can easily explore where it happened now debug X is not the only service for this you can find plenty of reg X debugging tools and they are all cool and sometimes a reg X is better visualized by one of the others I just happen to use teabag X mostly no particular reason you