Computer Old Farts Forum
 help / color / mirror / Atom feed
From: Dan Cross <crossd@gmail.com>
To: Ralph Corderoy <ralph@inputplus.co.uk>
Cc: coff@tuhs.org
Subject: [COFF] Re: Requesting thoughts on extended regular expressions in grep.
Date: Fri, 3 Mar 2023 08:11:23 -0500	[thread overview]
Message-ID: <CAEoi9W7D49pdoKXMruSLUp7QO7468FkmwL2E715Nu=DfSHWhmQ@mail.gmail.com> (raw)
In-Reply-To: <20230303105928.E88AB215AA@orac.inputplus.co.uk>

On Fri, Mar 3, 2023 at 5:59 AM Ralph Corderoy <ralph@inputplus.co.uk> wrote:
> [snip]
>
> If you want to understand:
>
> - the maths of regular expressions,
> - the syntax of regexps which these days expresses more than REs, and
> - the regexp engines in programs, the differences in how they work and
>   what they match, and
> - how to efficiently steer an engine's internals
>
> then I recommend Jeffrey Friedl's Mastering Regular Expressions.
> http://regex.info/book.html

I'm afraid I must sound a note of caution about Friedl's book.  Russ
Cox alludes to some of the problems in the "History and References"
section of his page (https://swtch.com/~rsc/regexp/regexp1.html), that
was linked earlier, and he links to this post:
http://regex.info/blog/2006-09-15/248

The impression is that Friedl shows wonderfully how to _use_ regular
expressions, but does not understand the theory behind their
implementation.

It is certainly true that today what many people refer to as "regular
expressions" are not in fact regular (and require a pushdown automata
to implement, putting them somewhere between REs and the context-free
languages in terms of expressiveness).

Personally, I'd stick with Russ's stuff, especially as `egrep` is the
target here.

        - Dan C.

  reply	other threads:[~2023-03-03 13:12 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-02 18:54 [COFF] " Grant Taylor via COFF
2023-03-02 19:23 ` [COFF] " Clem Cole
2023-03-02 19:38   ` Grant Taylor via COFF
2023-03-02 23:01   ` Stuff Received
2023-03-02 23:46     ` Steffen Nurpmeso
2023-03-03  1:08     ` Grant Taylor via COFF
2023-03-03  2:10       ` Dave Horsfall
2023-03-03  3:34         ` Grant Taylor via COFF
2023-03-02 21:53 ` Dan Cross
2023-03-03  1:05   ` Grant Taylor via COFF
2023-03-03  3:04     ` Dan Cross
2023-03-03  3:53       ` Grant Taylor via COFF
2023-03-03 13:47         ` Dan Cross
2023-03-03 19:26           ` Grant Taylor via COFF
2023-03-03 10:59 ` Ralph Corderoy
2023-03-03 13:11   ` Dan Cross [this message]
2023-03-03 13:42     ` Ralph Corderoy
2023-03-03 19:19       ` Grant Taylor via COFF
2023-03-04 10:15         ` [COFF] Reading PDFs on a mobile. (Was: Requesting thoughts on extended regular expressions in grep.) Ralph Corderoy
2023-03-07 21:49           ` [COFF] " Tomasz Rola
2023-03-07 22:46             ` Tomasz Rola
2023-06-20 16:02           ` Michael Parson
2023-06-20 21:26             ` Tomasz Rola
2023-06-22 15:45               ` Michael Parson
2023-07-10  9:08                 ` [COFF] Re: Reader, paper, tablet, phone (was: Re: Reading PDFs on a mobile. (Was: Requesting thoughts on extended regular expressions in grep.)) Tomasz Rola
2023-03-03 16:12   ` [COFF] Re: Requesting thoughts on extended regular expressions in grep Dave Horsfall
2023-03-03 17:13     ` Dan Cross
2023-03-03 17:38       ` Ralph Corderoy
2023-03-03 19:09         ` Dan Cross
2023-03-03 19:36     ` Grant Taylor via COFF
2023-03-04 10:26       ` Ralph Corderoy
2023-03-03 19:06 ` Grant Taylor via COFF
2023-03-03 19:31   ` Dan Cross
2023-03-04 10:07   ` Ralph Corderoy
2023-03-06 10:01 ` Ed Bradford
2023-03-06 21:01   ` Dan Cross
2023-03-06 21:49     ` Steffen Nurpmeso
2023-03-07  1:43     ` Larry McVoy
2023-03-07  4:01       ` Ed Bradford
2023-03-07 11:39         ` [COFF] " Ralph Corderoy
2023-03-07 18:31           ` [COFF] " Grant Taylor via COFF
2023-03-08 11:22           ` Ed Bradford
2023-03-07 16:14         ` Dan Cross
2023-03-07 17:34           ` [COFF] " Ralph Corderoy
2023-03-07 18:33             ` [COFF] " Dan Cross
2023-03-07  4:19     ` Ed Bradford

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAEoi9W7D49pdoKXMruSLUp7QO7468FkmwL2E715Nu=DfSHWhmQ@mail.gmail.com' \
    --to=crossd@gmail.com \
    --cc=coff@tuhs.org \
    --cc=ralph@inputplus.co.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).