SoylentNews is people
SoylentNews
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) "$" is a regular expression which matches character before the character (usually at the end of a line)
QED was the precursor to ed, which was instrumental in popularizing regexes, so a lot of its design choices stuck.
Okay, but then why did Ken Thompson choose those characters?
This discussion was created by janrinok (52) for logged-in users only, but now has been archived.
No new comments can be posted.
Why Do Regexes Use `$` and `^` as Line Anchors?
|
Log In/Create an Account
| Top
| 63 comments
| Search Discussion
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
Before you ask more questions, think about whether you really want to
know the answers.
-- Gene Wolfe, "The Claw of the Conciliator"
(Score: 5, Interesting) by Rosco P. Coltrane on Wednesday March 27 2024, @11:00PM (2 children)
I wasn't answering the question, just pointing out that whatever weird choices people of yesteryear made for whatever reason still echo in software of today.
Vi of course is the next evolutionary step after ed, so it's normal that is uses ^and $ for the same purpose as ed.
It's just that... Think about it: you can install vim and any modern system today - and I do mean ANY system: there's a port of vim for every OS known to man - and you can still hit ^and $ for quick navigation.
I bet Ken Thompson picked those characters on a whim. I pick command and command line arguments on a whim too when I write utilities at my company, and years down the line, they've turned into a sort of de-facto "standard" within my company. It never ceases to amaze me.
Similarly, I bet Ken Thompson never ceases to be amazed that his split-second decisions of decades ago are used far and wide all over the world, on every OS, by millions of people, so long after he made those split-second decisions.
Still, whatever the reason, the fact is that Unix tools are very consistent. I learned those conventions at school and I still use them today, only a few years away from retirement. I would argue that this is the ultimate user-friendliness - and as the saying goes, Unix is very user-friendly, it's just very particular with which friends it chooses 🙂
(Score: 4, Informative) by KritonK on Thursday March 28 2024, @06:40AM (1 child)
Although I do use $ to go to the end of the line, I use 0 to go to the beginning of the line. It's much easier to type.
(Score: 4, Informative) by Geoff Clare on Friday March 29 2024, @11:03AM
They are actually slightly different. If the line is indented, 0 goes to the very beginning but ^ goes to the first character after the indent.