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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: 2) by martyb on Wednesday March 27, @11:11PM (3 children)

    by martyb (76) Subscriber Badge on Wednesday March 27, @11:11PM (#1350587) Journal

    I can vouch for that! I learned to program using a (60?) column, continuous feed output (having 500 lines? inches?).

    Earplug were optional, but recommended! Then again, the computer was a multiprocessing, multi-user PDP/8E having ~24KB of *core* memory!

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  • (Score: 4, Funny) by janrinok on Wednesday March 27, @11:22PM

    by janrinok (52) Subscriber Badge on Wednesday March 27, @11:22PM (#1350590) Journal
    SPEAK UP - I can't hear you over the noise of the teleprinter!
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  • (Score: 4, Funny) by Rosco P. Coltrane on Wednesday March 27, @11:44PM (1 child)

    by Rosco P. Coltrane (4757) on Wednesday March 27, @11:44PM (#1350597)

    You kids had it easy. When I learned programming, we had to punch the cards with a hammer and a chisel!