Re: regex help wanted

> On 2013-04-25, Karsten Hilbert <Karsten.Hilbert@gmx.net> wrote:
>> On Thu, Apr 25, 2013 at 10:32:26AM -0400, Tom Lane wrote:
>>
>>> Karsten Hilbert <Karsten.Hilbert@gmx.net> writes:
>>> > What I don't understand is: Why does the following return a
>>> > substring ?
>>>
>>> >     select substring ('junk $<allergy::test::99>$ junk' from
>>> '\$<[^<]+?::[^:]+?>\$');
>>>
>>> There's a perfectly valid match in which [^<]+? matches allergy::test
>>> and [^:]+? matches 99.
>>
>> Tom, thanks for helping !
>>
>> I would have thought "<[^<]+?:" should mean:
>>
>>     match a "<"
>>     followed by 1-n characters as long as they are not "<"
>>     until the VERY NEXT ":"
>
>
> if you want that say:  "<[^<:]+:"
>
>> The "?" should make the "+" after "[^<]" non-greedy and thus
>> stop at the first occurrence of ":", right ?  Or am I
>> misunderstanding that part ?

Greediness and non-greediness of operators are like hints - they are only
honoured if there is a choice in the matter.  In your case, if the
<[^<]+?: stopped at the first ":", it would be impossible to match the
rest of the pattern.