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Why Do Regexes Use `$` and `^` as Line Anchors?

posted by janrinok on Wednesday March 27 2024, @08:12PM   Printer-friendly
from the I-didn't-know-that-... dept.

owl writes:

https://buttondown.email/hillelwayne/archive/why-do-regexes-use-and-as-line-anchors/

Last week I fell into a bit of a rabbit hole: why do regular expressions use $ and ^ as line anchors?1

This talk brings up that they first appeared in Ken Thompson's port of the QED text editor. In his manual he writes: b) "^" is a regular expression which matches character at the beginning of a line.

c) "$" is a regular expression which matches character before the character (usually at the end of a line)

QED was the precursor to ed, which was instrumental in popularizing regexes, so a lot of its design choices stuck.

Okay, but then why did Ken Thompson choose those characters?

Original Submission

 
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  • (Score: 2, Interesting) by shrewdsheep on Thursday March 28 2024, @10:11AM (2 children)

    by shrewdsheep (5215) on Thursday March 28 2024, @10:11AM (#1350654)

    Why the quip? The thread earlier was lining up against any change to the website. In view of the future of the site, I strongly support CSS optimizations and the use of limited javascript to improve usability. The old style can and should always be retained as a tribute to the legacy of the site. The user base has to be broadened for long term survival of SN and I believe that appearance and usability is a good part of it when it comes to attract new readership.

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  • (Score: 4, Informative) by janrinok on Thursday March 28 2024, @10:54AM (1 child)

    by janrinok (52) Subscriber Badge on Thursday March 28 2024, @10:54AM (#1350657) Journal

    It was merely asking who would be doing this task? To have selectable CSS pages will require significant Perl code changes and new fields adding to the database so that the user's choice is remembered between log-ins. The displays are created by templates which might have to be changed to cope with different CSS. It is not my area.

    No offence was intended. I did include a grin!

    --
    I am not interested in knowing who people are or where they live. My interest starts and stops at our servers.

    • (Score: 2, Interesting) by Anonymous Coward on Thursday March 28 2024, @04:42PM

      by Anonymous Coward on Thursday March 28 2024, @04:42PM (#1350716)

      To have selectable CSS pages will require significant Perl code changes and new fields adding to the database so that the user's choice is remembered between log-ins.

      User-selectable alternate stylesheets were an original design feature of CSS but it's unfortunate that the browser support today is completely useless.

      The CSS2 specification actually says that user agents must provide an interface to change between alternate stylesheets [w3.org]. I don't know if this requirement persists in current specifications. Firefox has the choice in a hidden menu but it forgets your selection as soon as you reload the page or follow any link so it's basically unusable. Such a shame.