Tom,
Thanks very much for that explanation and the link. That
explains the %(whatever)s part of the expression, but what
about the (?: ... ) ...is that Python too? Does it mean
to interpret whatever is enclosed in this expression as
"Python" first - rather than as a regular expression? If so,
would you happen to know what that operator is called in Python
...or better yet would you be able to point me in the direction
of a Python doc that explains it?
Thank you very much!
On Thu, Nov 24, 2016, at 12:41 PM, Tom Hendrikx wrote:
> Hi,
>
> That is indeed not regular expression syntax, it is python string
> formatting, used to generate the regex. This string is used also in the
> fail2ban config files in various distros to setup jails (although I
> think that the config file gets less readable from this, especially for
> non-programmers, but none of that is related to your question).
>
> See
> https://docs.python.org/3/library/stdtypes.html#printf-style-string-formatting
> for details on %(...)s syntax.
>
> Regards,
> Tom
>
> On 24-11-16 21:17, [email protected] wrote:
> > Hello,
> > I'm new to this list. I'm familiar with regular expressions but
> > there's one aspect of failregex's that I do not understand - the nesting
> > aspect. Take, for instance, this example from "apache-badbots.conf"
> > which comes with the installer in the filters.d/ directory:
> >
> > badbotscustom = EmailCollector|WebEMailExtrac|TrackBack/1\.02|sogou
> > music spider
> > badbots =
> > Atomic_Email_Hunter/4\.0|atSpider/1\.0|autoemailspider|bwh3_user_agent
> > ...etc...etc...etc...
> >
> > failregex = ^<HOST>
> > -.*"(GET|POST|HEAD).*HTTP.*"(?:%(badbots)s|%(badbotscustom)s)"$
> >
> >
> > The part that I don't understand is this:
> > "(?:%(badbots)s|%(badbotscustom)s)"
> > ...If that is a part of standard Posix regular expressions (or perl
> > extensions), I was not aware of it. So what is it? I can see that the
> > "%(badbots)" is probably getting replaced by the big long or'ed regular
> > expression above ...but what about the "s" after the last closing
> > parenthesis? And I do not understand the "(? ... )" ...what does it
> > mean to have an expression that is entirely enclosed in this
> > parenthesized expression with a question mark after the first opening
> > parenthesis?
> >
> > Thanks in advance for any help.
> >
> >
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> >
>
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