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Regex character "$" doesn't mean "end-of-string"

sethmlarson.dev

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Re: Regex character "$" doesn't mean "end-of-string"

#31

Post by skrebbel »

pjc50 wrote: post #21

Special misery case: Visual Studio supports regex search, where '$' matches \n. The end of line character is usually the standard Windows \r\n. Yes, that means if you want to really match the end of line you have to match "\r$". So broken.

FWIW, and I know this doesn't really address your complaint: I use Windows and I've set all my text editors to use LF exclusively years ago and Things Are Great. No more weird Git autocrlf warnings, no quirks when copying files over to/from people on Macs or Linuxes, etc. Even Notepad supports LF line endings for quite a long time now - to my practical experience, there's little remaining in Windows that makes CRLF "the OS standard line ending".

I bet if someday VS Code's Windows build ships with LF default on new installations, people won't even notice.

I mean, at some point it did matter what the OS did when you pressed the "Enter" button. But this isn't really the case much anymore. VS Code catches that keypress, and inserts whatever "files.eol" is set to. Sublime does the same. I didn't check, but I assume every other IDE has this setting.

Similarly, the HTML spec, which is pretty nuts, makes browsers normalize my enters to LF characters as I type into this textarea here (I can check by reading the `value` property in devtools), but when it's submitted, it converts every LF to a CRLF because that's how HTML forms were once specced back in the day. Again though, what my OS considers to be "the standard newline" is simply not considered at all. Even CMD.EXE batch files support LF.

I don't really type newlines all that much outside IDEs and browsers (incl electron apps) and places like MS Word, all of which disregard what the OS does and insert their own thing. Maybe the terminal? I don't even know. I doubt it's very consequential.

EDIT: PSA the same holds for backslashes! Do Not Use Backslashes. Don't use "OS specific directory separator constants". It's not 1998, just type "/" - it just works.

Re: Regex character "$" doesn't mean "end-of-string"

#32

Post by usrusr »

telotortium wrote: post #15
beardyw wrote: post #12

Does anyone consider RegEx to be standardised? Moving to a new context is always a relearning exercise in my experience.

Languages invented after Perl will generally use some flavor of Perl regex syntax, but there are always some minor differences. The issue of the meaning of `$` and changing it via multi-line mode is usually consistent though.

I like to think of "whatever browsers do in js" as an updated common baseline. Whatever your regex engine does, describe it as a delta to the js precedent. That thing is just so ubiquitous.

I do wonder though what's the highest number of different regex syntaxes I've ever encountered (perhaps written?) within a single line: bash, grep and sed are never not in a "hold my beer" mood!

Re: Regex character "$" doesn't mean "end-of-string"

#33

Post by jasonjayr »

beardyw wrote: post #12

Does anyone consider RegEx to be standardised? Moving to a new context is always a relearning exercise in my experience.

The three big ones I know of are POSIX, Perl/PCRE(aka Perl-Compatible Regular Expression), and Go came along and added used re2, which is a bit different from the first too.

A lot of systems implemented PCRE, including JavaScript, since Perl extended the POSIX system with many useful extensions. IIRC, re2 tries to reign in on some of the performance issues and quirks the original systems had, while implementing the whole thing in Go.

edit: Did not realize re2 predated go ...

Re: Regex character "$" doesn't mean "end-of-string"

#35

Post by tankenmate »

susam wrote: post #20
rusk wrote: post #14

Earlier quoted context omitted.

My understanding is it was standardised for Posix but the variants in popular use have so many variations. I consider sed to be the baseline. If you can do sed you can do anything but it’s seriously limited.

POSIX specifies two flavours of regular expressions: basic regular expressions (BRE) and extended regular expressions (ERE). There are subtle differences between the two and ERE supports more features than BRE. For example, what is written as a\(bc\)\{3\}d in BRE is written as a(bc){3}d in ERE. See https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1... for more details. The regular expression engines availab…

Indeed, and the most common is Perl since it was the source of many of the extensions.

Re: Regex character "$" doesn't mean "end-of-string"

#37

Post by jbverschoor »

pjc50 wrote: post #21

Special misery case: Visual Studio supports regex search, where '$' matches \n. The end of line character is usually the standard Windows \r\n. Yes, that means if you want to really match the end of line you have to match "\r$". So broken.

The whole \r is archaic. It doesn't even behave properly in most cases. Just use \n everywhere and bite the lemon for a short while to fix your problems.

And if you believe \r\n is the way to go, please make sure \n\r also works as they should have the same results. (or \r\n\r\r\r\r for that matter)

Re: Regex character "$" doesn't mean "end-of-string"

#38

Post by zimpenfish »

ghusbands wrote: post #18

> Note: The table of data was gathered from regex101.com, I didn't test using the actual runtimes. Has anyone confirmed this behaviour directly against the runtimes/languages? Newlines at the end of a string are certainly something that could get lost in transit inside an online service involving multiple runtimes.

https://go.dev/play/p/Tce1qWjfjOy matches their results.

I've also run that locally against "go1.22.1 darwin/arm64", "go1.21.5 windows/amd64", and "go1.21.0 linux/amd64" with the same result.

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