Le 07/03/2011 15:13, Stan Hoeppner a écrit :
> Noel Jones put forth on 3/7/2011 7:00 AM:
>> On 3/7/2011 4:47 AM, Stan Hoeppner wrote:
>>>
>>> I was taught to always start my expressions with "/^" and end them with
>>> "$/". Why did Steven teach me to do this if it's not necessary?
>>
>> That's good advice when you're actually matching something.
>
> Ok, so if I'm doing what I've heard called a "fully qualified regular
> expression", WRT FQrDNS matching, should I use the anchors or not?
> postmap -q says these all work (the actuals with action and text that is).
>
> /^(\d{1,3}-){3}\d{1,3}\.dynamic\.chello\.sk$/
.dynamic.chello.sk REJECT blah blah
> /^(\d{1,3}\.){4}dsl\.dyn\.forthnet\.gr$/
.dyn.forthnet.gr REJECT blah blah
> /^(\d{1,3}-){4}adsl-dyn\.4u\.com\.gh$/
/dyn\.4u.com\.gh$/ REJECT blah
assuming you get real mail from there. otherwise
.4u.com.gh REJECT blah
> /^[\d\w]{8}\.[\w]{2}-[\d]-[\d\w]{2}\.dynamic\.ziggo\.nl$/
ahem? I fail to see what yoy're trying to match here. \d is a \w, so
[\d\w] is the same as \w. do you mean \W (capital letter)? anyway:
.dynamic.ziggo.nl REJECT blah blah
> /^(\d{1,3}\.){4}dynamic\.snap\.net\.nz$/
.dynamic.snap.net.nz REJECT blah
> /^pppoe-dyn(-\d{1,3}){4}\.kosnet\.ru$/
/\Wdyn\W.*\.kosnet\.ru$/ REJECT blah
>
>> The special case of .* means, as you know, "anything or nothing".
>> There's never a case where it's necessary to explicitly match a leading
>> or trailing "anything or nothing".
>
> What of the case where you want to match something in the middle of the
> input string, with extra junk on both ends?
well, that's what regular expressions are about by default:
/foo/ means contains foo
/^foo/ means starts with foo
/foo$/ means ends with foo
so
/^bart.*homer.*marge$/ means: starts with "bart", ends with "marge" and
somewhere between these contains "homer".
>
>> Consider:
>> /^.*foo$/
>> match the string beginning with anything or nothing, ending with foo.
>>
>> can always be simplified to:
>> /foo$/
>> match the string ending with foo.
>>
>> This works the same without the ending $ anchor (contains foo, rather
>> than ends with foo), but helps the illustration.
>
> So, in my examples above, given we're matching rDNS patterns, are the
> anchors necessary, or helpful? If not using them means "contains", then
> they should still match. What advantage is there to using the anchors
> when matching rDNS patterns? Any?
>
>> (In the other special case where you're using $1, $2, etc. substitution
>> in the result, you might need some form of /^(.*foo)$/ to fill the
>> substitution buffer, but that's about substitution, not about matching.)
>
> Thank you for the continuing PCRE education Noel, and Ansgar. :)
>
