Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

sethmlarson.dev

Post reply on HN
Print view View original

121–130 of 382 posts

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

#121

Post by danbruc »

masklinn wrote: post #117
danbruc wrote: post #111

Earlier quoted context omitted.

It is start and end of line. [1] Usually ^ matches only at the beginning of the string, and $ matches only at the end of the string and immediately before the newline (if any) at the end of the string. When this flag is specified, ^ matches at the beginning of the string and at the beginning of each line within the string, immediately following each newline. Similarly, the $ metacharacter matches either at the end of…

> It is start and end of line. You seem to have redefined “line” as “not a line”. > The confusion I’m sure redefining “line” as “nothing like what anyone reasonable would interpret as a line” will help a lot and right clear up the confusion.

The POSIX definition of a line is a sequence of non-newline characters - possibly zero - followed by a newline. Everything that does not end with a newline is not a [complete] line. So strictly speaking it would even be correct that cat$ does not match cat because there is no terminating newline, it should only match cat\n. But as lines missing a terminating newline is a thing, it seems reasonable to be less strict.

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

#122

Post by zaxomi »

criley2 wrote: post #87
thecatspaw wrote: post #82

Earlier quoted context omitted.

what does gpt say how we should validate email addresses?

Prompt: 'I'm writing a nodejs javascript application and I need a regex to validate emails in my server. Can you write a regex that will safely and efficiently match emails?' GPT4 / Gemini Advanced / Claude 3 Sonnet GPT4: `const emailRegex = /^[a-zA-Z0-9._-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;` Full answser: https://justpaste.it/cg4cl Gemini Advanced: `const emailRegex = /^[a-zA-Z0-9.!#$%&' +/=?^_`{|}~-]+@[a-zA-Z0-9](?:…

Still doesn't support internationalized domain names.

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

#123

Post by [deleted] »

masklinn wrote: post #117
danbruc wrote: post #111

Earlier quoted context omitted.

It is start and end of line. [1] Usually ^ matches only at the beginning of the string, and $ matches only at the end of the string and immediately before the newline (if any) at the end of the string. When this flag is specified, ^ matches at the beginning of the string and at the beginning of each line within the string, immediately following each newline. Similarly, the $ metacharacter matches either at the end of…

> It is start and end of line. You seem to have redefined “line” as “not a line”. > The confusion I’m sure redefining “line” as “nothing like what anyone reasonable would interpret as a line” will help a lot and right clear up the confusion.

[deleted]

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

#124

Post by burntsushi »

m0rissette wrote: post #107

Why isn’t Perl anywhere on that chart when mentioning regex?

Because they're using regex101 to easily test the semantics of different regex engines and Perl isn't available on regex101. PCRE is though, which is a decent approximation. And indeed, Perl and PCRE behave the same for this particular case.

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

#125

Post by CatchSwitch »

PuffinBlue wrote: post #42

This seems like the perfect opportunity to introduce those unfamiliar to Robert Elder. He makes cool YouTube[0] and blog content[1] and has a series on regular expressions[2] and does some quite deep dives into the differing behaviour of the different tools that implement the various versions. His latest on the topic is cool too: https://www.youtube.com/watch?v=ys7yUyyQA-Y He's has quite a lot of content that HN folk…

He has so many favorite Linux commands lol

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

#127

Post by [deleted] »

berkes wrote: post #95
username_my1 wrote: post #61

Earlier quoted context omitted.

regex is useful but chatgpt is amazing at it, so why spend a minute keeping such useless knowledge in mind. if you know where to find something no point in knowing it.

> if you know where to find something no point in knowing it. Nonsense. And you know it. First, you need to know what to find, before knowing where to find it. And knowing what to find requires intricate knowledge of the thing. Not intricate implementation details, but enough to point yourself in the right direction. Secondly, you need to know why to find thing X and not thing Y. If anything, ChatGPT is even worse th…

[deleted]

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

#128

Post by wodenokoto »

iainmerrick wrote: post #80
wodenokoto wrote: post #72

> So if you're trying to match a string without a newline at the end, you can't only use $ in Python! My expectation was having multiline mode disabled wouldn't have had this newline-matching behavior, but that isn't the case. A reproducible example would be nice. I don’t understand what it is he cannot do. `re.search('$', 'no new lines')` returns a match.

This unexpectedly matches: re.match('^bob$', 'bob\n') I didn't want the trailing newline to be included.

But that string does have a new line at the end.

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

#130

Post by [deleted] »

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…

[deleted]
Post reply on HN