Understanding matches in sieve

[Robert L Mathews]

On 10/21/20 11:15 AM, @lbutlr wrote:
> RFC 5229 gives the following example:
> 
> if address :matches ["To", "Cc"] ["coyote@**.com",
>               "wile@**.com"] {
>           # ${0} is the matching address
>           # ${1} is always the empty string
>           # ${2} is part of the domain name ("ACME.Example")
>           fileinto "INBOX.business.${2}"; stop;
> 
> And I do not understand why ${1} is always the empty string.

This is because of the text above that: "The wildcards match as little
as possible (non-greedy matching)."

This example has two wildcards in a row (""**" doesn't mean anything
special beyond that) -- and because the first "*" matches as little as
possible, it matches nothing (the empty string). The second "*" matches
everything between "@" and ".com".

The same thing happens with real regexps:

 #!/usr/bin/perl
 $x = 'coyote at ACME.Example.COM';
 $x =~ /coyote\@(.*?)(.*?)\.COM/;
 printf '$1 is "%s"; $2 is "%s"', $1, $2;

This will print:

 $1 is ""; $2 is "ACME.Example"


> I am laso not sure why the first example used **.com instead of *.com (or is that the reason $1 doesn't contain anything because it is the first * of **?).

Yes. The example is confusing because it makes it look like "**" is some
magic thing you might want to use. It's not.

-- 
Robert L Mathews, Tiger Technologies, http://www.tigertech.net/