Sieve Rule weirdness

[hbs]

:domain takes the domain part from the address without the "@".

So "@linkedin.com" would never match.

[JamesHenderson]

got it - thanks!

[SideshowBob]

Originally Posted by xyzzy

"@linkedin\\.com$"

As a regex that will never work. That does not test for an email address local part (part before the @). So the complete regex would be

".+@(.*\\.)?linkedin\\.com$"

You need the * with :matches because you need to match the whole string. regexes match on substings unless you anchor them, hence the "$". Your ".+" makes no difference at all here.

[JamesHenderson]

so, using :domain, I got this to work which is fairly simple as no need to worry about the "@" anymore.

  address :domain :regex "From" "\\.*linkedin\\.com$",

[hbs]

Can't help with the why, but FM needs the double backslashes.

I got curious myself and found it. The double-backslash is actually defined in RFC 5228, section 2.4.2.

So, Fastmail aren't the ones to blame.

[BritTim]

Originally Posted by JamesHenderson

so, using :domain, I got this to work which is fairly simple as no need to worry about the "@" anymore.

  address :domain :regex "From" "\\.*linkedin\\.com$",

You should be aware that the above code is exactly equivalent to

address :domain :regex "From" "linkedin\\.com$",

In both cases you are saying that the domain must end in linkedin.com with anything prior to this being irrelevant. Note that, if you want to ensure that the domain name is not something like xlinkedin.com or xxx.ylinkedit.com (correct, I guess, but maybe overkill) the correct solution depends on the precise details of the regex support provided. It can be quite tricky.

[JamesHenderson]

Originally Posted by JamesHenderson

so, using :domain, I got this to work which is fairly simple as no need to worry about the "@" anymore.

  address :domain :regex "From" "\\.*linkedin\\.com$",

as did this:

address :regex "From" "[\\.@]linkedin\\.com$",

...and I think this was what I was imagining from the start when I wrote:

address :matches "From" "*[.@]linkedin.com",

[JamesHenderson]

Originally Posted by BritTim

You should be aware that the above code is exactly equivalent to

address :domain :regex "From" "linkedin\\.com$",

In both cases you are saying that the domain must end in linkedin.com with anything prior to this being irrelevant. Note that, if you want to ensure that the domain name is not something like xlinkedin.com or xxx.ylinkedit.com (correct, I guess, but maybe overkill) the correct solution depends on the precise details of the regex support provided. It can be quite tricky.

agh, yes of course- thanks for pointing that out.
So I don't really want to use :domain as I want the first character to be either an "@" or a "."

...works out for me because actually I am putting these rules into the UI (minus the double slashes as FM adds them for me) and I cannot find a way to have "domain in the UI.

[JamesHenderson]

thanks to everyone for their kind and friendly support in solving my problem and helping me learn in the process :-)

[SideshowBob]

Originally Posted by JamesHenderson

Thanks, xyzzy.

I got the gist of your code (thanks). but my question was specifically why two slahes were needed in succession. I can see that Fastmail translates my single slash into two, but why? ...I cannot see any reference to double-shlashing having a special meaning in regex (it seems to me that the first slash escapes the second slash).

It's because the escaping is happening at two separate levels.

In sieve a \ is used to escape the double quote character that's normally the string delimiter, and a literal \ itself has to be escaped as \\. Other backslashes are ignored. This is done before the regex string is passed to the regex library.

[JamesHenderson]

Brilliant - thanks for that explanation, SideshowBob