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

posted by janrinok on Wednesday March 27, @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?

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  • (Score: 2) by krishnoid on Thursday March 28, @09:32PM

    by krishnoid (1156) on Thursday March 28, @09:32PM (#1350761)

    Citations requested. There's a lot of value in being able to distinguish which decisions were made quickly [computer.org] from ones that were released after a careful design process, and how they anti/correlate to the quality of the result.

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