[TUHS] Regular Expressions

Bakul Shah bakul at iitbombay.org
Sat Aug 1 11:31:39 AEST 2020

I was trying to get Will to try simple stuff out himself from first principles (to get started) but this is of course far better!

> On Jul 31, 2020, at 5:36 PM, Rob Pike <robpike at gmail.com> wrote:
> I think this link -  https://swtch.com/~rsc/regexp/regexp1.html <https://swtch.com/~rsc/regexp/regexp1.html> i- s the best place to start. Superb exposition on the background, theory, and implementation as well as a bit of history of how the industry lost its way with regular expressions.
> Regular expressions are beautiful, simple, and widely misunderstood.
> -rob
> On Sat, Aug 1, 2020 at 10:03 AM Bakul Shah <bakul at iitbombay.org <mailto:bakul at iitbombay.org>> wrote:
> On Jul 31, 2020, at 3:57 PM, Will Senn <will.senn at gmail.com <mailto:will.senn at gmail.com>> wrote:
> > 
> > I've always been intrigued with regexes. When I was first exposed to them, I was mystified and lost in the greediness of matches. Now, I use them regularly, but still have trouble using them. I think it is because I don't really understand how they work.
> > ...
> > 1. What's the provenance of regex in unix (when did it appear, in what form, etc)?
> > 2. What are the 'best' implementations throughout unix (keep it pre 1980s)?
> > 3. What are some of the milestones along the way (major changes, forks, disagreements)?
> > 4. Where, in the source, or in a paper, would you point someone to wanting to better understand the mechanics of regex?
> Start here: https://en.wikipedia.org/wiki/Thompson%27s_construction <https://en.wikipedia.org/wiki/Thompson%27s_construction>
> [I learned about regular expressions in an automata theory class, 
>  before I knew anything about Unix. What helped me was learning
>  about finite state machines. You won't need more than paper and
>  pencil to construct one. Reading source code would make more
>  sense once you grasp how to construct a FSM corresponding to a RE.]

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