[TUHS] Regular Expressions

Will Senn will.senn at gmail.com
Sat Aug 1 12:33:39 AEST 2020

Yes, I googled it per Clem's suggestion and wound up on that exact link 
after wandering around admiring the scenery. I envy the more 
mathematically inclined among us their view of matters technical. This 
piece, being in C and having step by step articulation of the diagrams, 
is better for me than the more formal wikipedia article, although, when 
I get enough background, that looks like it'll be good, too.

Thanks Rob, Clem and Bakul.


On 7/31/20 7:36 PM, Rob Pike wrote:
> I think this link - 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
>     [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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