[TUHS] Regular Expressions

John P. Linderman jpl.jpl at gmail.com
Sat Aug 1 10:53:43 AEST 2020

Hear hear. And I think it should be possible to analyze regular expressions
to determine if "simple" (hence fast) regexps are adequate. "Fancy" re's
are rare. At least from those of us where they couldn't be expressed.

On Fri, Jul 31, 2020 at 8:38 PM Rob Pike <robpike at gmail.com> 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> 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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