[TUHS] Regular Expressions

Rob Pike robpike at gmail.com
Sat Aug 1 10:36:48 AEST 2020

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.


On Sat, Aug 1, 2020 at 10:03 AM Bakul Shah <bakul at iitbombay.org> wrote:

> On Jul 31, 2020, at 3:57 PM, Will Senn <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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