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Title    Why Do Regexes Use `$` and `^` as Line Anchors?
Date    Wednesday March 27, @08:12PM
Author    janrinok
Topic   
from the I-didn't-know-that-... dept.
https://soylentnews.org/article.pl?sid=24/03/26/165203

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

Links

  1. "owl" - https://soylentnews.org/~owl/
  2. "Original Submission" - https://soylentnews.org/submit.pl?op=viewsub&subid=62404

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