Stories
Slash Boxes
Comments

SoylentNews is people

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

 
This discussion was created by janrinok (52) for logged-in users only, but now has been archived. No new comments can be posted.
Why Do Regexes Use `$` and `^` as Line Anchors? | Log In/Create an Account | Top | 63 comments | Search Discussion
Display Options Threshold/Breakthrough Mark All as Read Mark All as Unread
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.

  • (Score: 2) by Rosco P. Coltrane on Thursday March 28 2024, @05:19PM

    by Rosco P. Coltrane (4757) on Thursday March 28 2024, @05:19PM (#1350727)

    Reading someone else's regexes is even more difficult; like APL, it's a write-only language.

    That's because programmers somehow forget all rules of readability when they write regexes for some reason.

    My regexes are spread over several lines and indented. You can read them just fine even if they're really complicated. I always take the time to make my code readable for everybody else as a common courtesy, and regexes are an integral part of my code, so they get the same treatment for the same purpose.

    Starting Score:    1  point
    Karma-Bonus Modifier   +1  
    Total Score:   2