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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: 3, Interesting) by Tork on Thursday March 28 2024, @12:23AM

    by Tork (3914) Subscriber Badge on Thursday March 28 2024, @12:23AM (#1350609) Journal
    I use this site mostly on an iPhone and one lil nuisance that does bug me is there's an extra 'scroll' that can happen on a page when I'm writing a reply. I don't know if it's something in the site's code or if Safari's just clowning around as it likes to do. I end up scrolling left and right a lot like a security camera to review before I post. I've never mentioned this before and never really intended to... so sorry for the crummy description of the issue. I do think that's partly why I occasionally a word from my posts fairly regularly. ;)

    Again I wasn't intending to raise this issue, I don't think it really needs to be fixed, it just became on-topic today. On a side note I do appreciate that the font shrinks as you go down the branch. Reading through threads works pretty well. It's one of the reasons I go here first before the green site.
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