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From: Ralph Corderoy <ralph@inputplus.co.uk>
To: coff@tuhs.org
Subject: [COFF] Re: Requesting thoughts on extended regular expressions in grep.
Date: Fri, 03 Mar 2023 10:59:28 +0000	[thread overview]
Message-ID: <20230303105928.E88AB215AA@orac.inputplus.co.uk> (raw)
In-Reply-To: <8d1de5c8-1f34-3d37-395d-0f1da7b062ec@spamtrap.tnetconsulting.net>

Hi Grant,

> What are the pros / cons to creating extended regular expressions like
> the following:

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

> For matching patterns like the following in log files?
>
>     Mar  2 03:23:38

Do you want speed of matching with some false positives or validation by
regexp rather than post-lexing logic and to what depth, e.g. does this
month have a ‘31st’?

    /^... .. ..:..:../

You'd said egrep, which is NDFA, but in other engines, alternation order
can matter, e.g. ‘J’ starts the most months and some months have more
days than others.

    /^(J(an|u[nl])|Ma[ry]|A(ug|pr)|Oct|Dec|...

-- 
Cheers, Ralph.

  parent reply	other threads:[~2023-03-03 10:59 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 [this message]
2023-03-03 13:11   ` Dan Cross
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

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