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

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?


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  • (Score: 2) by stormreaver on Thursday March 28, @12:54AM (3 children)

    by stormreaver (5101) on Thursday March 28, @12:54AM (#1350612)

    Three-column layouts, where the main content is in the center, were common well before cellphones became widespread. That layout is common because there is a point where horizontal reading becomes less pleasant than vertical reading.

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  • (Score: 3, Informative) by aafcac on Thursday March 28, @02:18AM (2 children)

    by aafcac (17646) on Thursday March 28, @02:18AM (#1350617)

    Yes, also remember that Xerox had their monitors in portrait format back when they were developing their paperless offices for a reason.

    It's also worth recognizing that in some places that format of multiple columns makes it easier to fold up to not interfere with other folks on the bus while reading the newspaper.

    • (Score: 2) by krishnoid on Thursday March 28, @09:27PM (1 child)

      by krishnoid (1156) on Thursday March 28, @09:27PM (#1350760)

      And the qwerty keyboard layout is designed to keep the hammers from jamming [dvzine.org].

      • (Score: 2) by aafcac on Friday March 29, @02:14PM

        by aafcac (17646) on Friday March 29, @02:14PM (#1350855)

        Yes, and unfortunately one of those two things can be easily remedied as needed. It's one of the reasons why it's worth having a good monitor stand, it should allow you to rotate the screen 90 degrees if you're doing something that benefits from that. Or, just have the window manager tile the window to only take up half of the width.

        The keyboard though is a much more annoying problem. Yes, you an use whatever map you like, so long as you have enough keys, but it's a whole thing to learn a new layout and if you're a decent typist it may not even be worth the effort.