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posted by janrinok on Wednesday March 27, @08:12PM   Printer-friendly
from the I-didn't-know-that-... dept.

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: 1) by zdammit on Thursday March 28, @08:10AM (2 children)

    by zdammit (5626) on Thursday March 28, @08:10AM (#1350647)

    I don't know about you but I find very wide text layouts hard to read and I like the sites that try to make it less wide. There is a typographic convention that says line width should be 2.x alphabets (x depends on who you ask).

  • (Score: 2) by VLM on Thursday March 28, @04:40PM

    by VLM (445) on Thursday March 28, @04:40PM (#1350714)

    It's been a battle for decades now, that source code should either be like literature or prose with short lines for the casual reader vs source code should be like a math formula where stretching one unitary concept into unneeded extra steps or extra lines is mere obfuscation to be avoided for the simplicity of one line for one concept.

  • (Score: 3, Touché) by owl on Thursday March 28, @07:31PM

    by owl (15206) on Thursday March 28, @07:31PM (#1350746)

    Then narrow your viewing window, and suddenly, you get "less wide" text layouts.

    The only reason you get very wide layouts is you have your browser window sized to be "very wide". I.e., the problem is completely under your control.