Re: [TUHS] Regular Expressions

[Larry McVoy <lm@mcvoy.com>]

That link is a great read.

On Sat, Aug 01, 2020 at 10:36:48AM +1000, 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@iitbombay.org> wrote:
> 
> > On Jul 31, 2020, at 3:57 PM, Will Senn <will.senn@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.]

-- 
---
Larry McVoy            	     lm at mcvoy.com             http://www.mcvoy.com/lm