11.1. Regular Expressions

14.1. Regular Expressions

Privoxy can use "regular expressions" - in various config files. Assuming support for uses Perl-style "pcre" (Perl - Compatible Regular Expressions) is compiled in, which is the default. Such - configuration directives do not require regular expressions, but they can be - used to increase flexibility by matching a pattern with wild-cards against - URLs.

"regular + expressions" in its actions + files and filter file, + through the PCRE and + PCRS libraries.

If you are reading this, you probably don't understand what "regular expressions" are, or what they can do. So this will be a very brief - introduction only. A full explanation would require a book ;-)

book ;-)

Regular expressions provide a language to describe patterns that can be + run against strings of characters (letter, numbers, etc), to see if they + match the string or not. The patterns are themselves (sometimes complex) + strings of literal characters, combined with wild-cards, and other special + characters, called meta-characters. The "Regular expressions" is a way of matching one character - expression against another to see if it matches or not. One of the +>"meta-characters" have + special meanings and are used to build complex patterns to be matched against. + Perl Compatible Regular Expressions are an especially convenient "expressions" is a literal string of readable characters - (letter, numbers, etc), and the other is a complex string of literal - characters combined with wild-cards, and other special characters, called - meta-characters. The "meta-characters" have special meanings and - are used to build the complex pattern to be matched against. Perl Compatible - Regular Expressions is an enhanced form of the regular expression language - with backward compatibility.

"dialect" of the regular expression language.

To make a simple analogy, we do something similar when we use wild-card characters when listing files with the

. - Matches any single character, e.g. "a"

? - The preceding character or expression is matched ZERO or ONE times. Either/or.

+ - The preceding character or expression is matched ONE or MORE times.

* - The preceding character or expression is matched ZERO or MORE times.

\ - The "escape"

[][ ] - Characters enclosed in brackets will be matched if any of the enclosed characters are encountered. For instance,

()( ) - parentheses are used to group a sub-expression, or multiple sub-expressions.

| - The "bar"
s/string1/string2/g - This is used to rewrite strings of text. - "string1" is replaced by "string2" in this - example. There must of course be a match on "string1" first. -
These are just some of the ones you are likely to use when matching URLs with
/.*/banners/.* - A simple example that uses the common combination of in the path somewhere.
A now something a little more complex:
And now something a little more complex:
/.*/adv((er)?ts?|ertis(ing|ements?))?/ - We have several literal forward slashes again (".*", so we are matching against any conceivable sub-path, just so - it matches our expression. The only true literal that must match our pattern is adv"ing" - OR "ements?", which would then match either spelling.
/.*/advert[0-9]+\.(gif|jpe?g) - Again another path statement with forward slashes. Anything in the square brackets "[]""[ ]" can be matched. This is using "0-9" is not in the expression anywhere).
s/microsoft(?!.com)/MicroSuck/i - This is - a substitution. "MicroSuck" will replace any occurrence of - "microsoft". The "i" at the end of the expression - means ignore case. The "(?!.com)" means - the match should fail if "microsoft" is followed by - ".com". In other words, this acts like a "NOT" - modifier. In case this is a hyperlink, we don't want to break it ;-).
We are barely scratching the surface of regular expressions here so that you can understand the default
More reading on Perl Compatible Regular expressions: http://www.perldoc.com/perl5.6/pod/perlre.htmlhttp://perldoc.perl.org/perlre.html
For information on regular expression based substitutions and their applications + in filters, please see the filter file tutorial + in this manual.
11.2. 14.2. Privoxy's Internal Pages
's Internal Pages
Since
Alternately, this may be reached at There is a shortcut: http://p.p/, but this - variation may not work as reliably as the above in some configurations. +> (But it + doesn't provide a fall-back to a real page, in case the request is not + sent through Privoxy)
Short cuts. Turn off, then on:
11.2.1. Bookmarklets14.2.1. Bookmarklets
Below are some
Privoxy - Submit Filter FeedbackPrivoxy - Why?
Credit: The site which gave me the general idea for these bookmarklets is +> Credit: The site which gave us the general idea for these bookmarklets is www.bookmarklets.com. They @@ -1075,8 +1073,8 @@ CLASS="SECT2" CLASS="SECT2" >11.3. Chain of Events14.3. Chain of Events
Let's take a quick look at the basic sequence of events when a web page is requested by your browser and Privoxy traps any request for its own internal CGI - pages (e.g http://p.p/) and sends the CGI page back to the browser. + pages (e.g http://p.p/) and sends the CGI page back to the browser.
Privoxy checks to see if the URL matches any "+block" patterns. If so, the URL is then blocked, and the remote web server will not be contacted. "+handle-as-image""BLOCKED" page is sent back. Otherwise, if it does match, an image is returned. The type of image depends on the setting of "+set-image-blocker"
If the URL pattern matches the "+fast-redirects"
Now the rest of the client browser's request headers are processed. If any of these match any of the relevant actions (e.g. "+hide-user-agent"
First, the server headers are read and processed to determine, among other things, the MIME type (document type) and encoding. The headers are then - filtered as deterimed by the + filtered as determined by the "+prevent-setting-cookies""+crunch-incoming-cookies", "+session-cookies-only", and "+downgrade-http-version"
If the "+kill-popups"
If a "+filter" or "+deanimate-gifs"default.filter) are processed against the buffered - content. Filters are applied in the order they are specified in the - default.filter file. Animated GIFs, if present, are - reduced to either the first or last frame, depending on the action +> and any other filter files) are + processed against the buffered content. Filters are applied in the order + they are specified in one of the filter files. Animated GIFs, if present, + are reduced to either the first or last frame, depending on the action setting.The entire page, which is now filtered, is then sent by
If neither "+filter" or "+deanimate-gifs"
As the browser receives the now (probably filtered) page content, it +> As the browser receives the now (possibly filtered) page content, it reads and then requests any URLs that may be embedded within the page source, e.g. ad images, stylesheets, JavaScript, other HTML documents (e.g. frames), sounds, etc. For each of these objects, the browser issues a new @@ -1314,34 +1300,28 @@ CLASS="SECT2" CLASS="SECT2" >11.4. Anatomy of an Action14.4. Anatomy of an Action
The way Privoxy applies "actions" - and "filters"actions and filters to any given URL can be complex, and not always so easy to understand what is happening. And sometimes we need to be able to - see just what Privoxy is doing is causing us a problem inadvertently. It can be a little daunting to look at the actions and filters files themselves, since they tend to be filled with - "regular expressions" whose consequences are not always - so obvious.
regular expressions whose consequences are not + always so obvious.
One quick test to see if the Bookmarklets section on a quick - and easy way to do this (be sure to flush caches afterward!).
will tell us how the current configuration will handle it. This will not help with filtering effects (i.e. the "+filter" action) from - the default.filter file since this is handled very + one of the filter files since this is handled very differently and not so easy to trap! It also will not tell you about any other URLs that may be embedded within the URL you are testing. For instance, images such as ads are expressed as URLs within the raw page source of HTML pages. So @@ -1419,7 +1396,8 @@ HREF="http://google.com" TARGET="_top" >google.com, - and look at it one section at a time:
Matches for http://google.com: ---- File standard --- -(no matches in this file) - ---- File default --- + In file: default.action [ View ][ Edit ] -{ -add-header -block +deanimate-gifs{last} -downgrade-http-version +fast-redirects - -filter{popups} -filter{fun} -filter{shockwave-flash} -filter{crude-parental} - +filter{html-annoyances} +filter{js-annoyances} +filter{content-cookies} - +filter{webbugs} +filter{refresh-tags} +filter{nimda} +filter{banners-by-size} - +hide-forwarded-for-headers +hide-from-header{block} +hide-referer{forge} - -hide-user-agent -handle-as-image +set-image-blocker{pattern} -limit-connect - +prevent-compression +session-cookies-only -prevent-reading-cookies - -prevent-setting-cookies -kill-popups -send-vanilla-wafer -send-wafer } + {-add-header + -block + -content-type-overwrite + -crunch-client-header + -crunch-if-none-match + -crunch-incoming-cookies + -crunch-outgoing-cookies + -crunch-server-header + +deanimate-gifs {last} + -downgrade-http-version + +fast-redirects {check-decoded-url} + -filter {js-events} + -filter {content-cookies} + -filter {all-popups} + -filter {banners-by-link} + -filter {tiny-textforms} + -filter {frameset-borders} + -filter {demoronizer} + -filter {shockwave-flash} + -filter {quicktime-kioskmode} + -filter {fun} + -filter {crude-parental} + -filter {site-specifics} + +filter {js-annoyances} + +filter {html-annoyances} + +filter {refresh-tags} + +filter {unsolicited-popups} + +filter {img-reorder} + +filter {banners-by-size} + +filter {webbugs} + +filter {jumping-windows} + +filter {ie-exploits} + -filter-client-headers + -filter-server-headers + -force-text-mode + -handle-as-empty-document + -handle-as-image + -hide-accept-language + -hide-content-disposition + +hide-forwarded-for-headers + +hide-from-header {block} + -hide-if-modified-since + +hide-referrer {forge} + -hide-user-agent + -inspect-jpegs + -kill-popups + -limit-connect + -overwrite-last-modified + +prevent-compression + -redirect + -send-vanilla-wafer + -send-wafer + +session-cookies-only + +set-image-blocker {pattern} + -treat-forbidden-connects-like-blocks } / - + { -session-cookies-only } .google.com { -fast-redirects } .google.com ---- File user --- +In file: user.action [ View ][ Edit ] (no matches in this file)

This tells us how we have defined our +> This is telling us how we have defined our "actions", and - which ones match for our example, "google.com". The first listing +>. + Displayed is all the actions that are available to us. Remember, + the + sign denotes "on". - + denotes "off". So some are "on" here, but many + are "off". Each example we try may provide a slightly different + end result, depending on our configuration directives.
The first listing is any matches for the standard.action".google.com". The first is negating our previous cookie setting, which was for "+session-cookies-only" - (i.e. not persistent). So we will allow persistent cookies for google. The - second turns off any "+fast-redirects" Then, for our user.action file, we again have no hits.
file, we again have no hits. + So there is nothing google-specific that we might have added to our own, local + configuration.
And finally we pull it all together in the bottom section and summarize how
Final results: - -add-header -block +deanimate-gifs{last} -downgrade-http-version -fast-redirects - -filter{popups} -filter{fun} -filter{shockwave-flash} -filter{crude-parental} - +filter{html-annoyances} +filter{js-annoyances} +filter{content-cookies} - +filter{webbugs} +filter{refresh-tags} +filter{nimda} +filter{banners-by-size} - +hide-forwarded-for-headers +hide-from-header{block} +hide-referer{forge} - -hide-user-agent -handle-as-image +set-image-blocker{pattern} -limit-connect - +prevent-compression -session-cookies-only -prevent-reading-cookies - -prevent-setting-cookies -kill-popups -send-vanilla-wafer -send-wafer

and "session-cookies-only", + which are activated specifically for this site in our configuration, + and thus show in the "Final Results".

Now another example, "+imageblock". ("Aliases""ad.doubleclick.net" is done here -- as both a "+block" - and an "+handle-as-image"

One last example. Let's try "http://www.rhapsodyk.net/adsl/HOWTO/""http://www.example.net/adsl/HOWTO/". - This one is giving us problems. We are getting a blank page. Hmmm...

Matches for http://www.rhapsodyk.net/adsl/HOWTO/: +> Matches for http://www.example.net/adsl/HOWTO/: - { -add-header -block +deanimate-gifs -downgrade-http-version +fast-redirects - +filter{html-annoyances} +filter{js-annoyances} +filter{kill-popups} - +filter{webbugs} +filter{nimda} +filter{banners-by-size} +filter{hal} - +filter{fun} +hide-forwarded-for-headers +hide-from-header{block} - +hide-referer{forge} -hide-user-agent -handle-as-image +set-image-blocker{blank} - +prevent-compression +session-cookies-only -prevent-setting-cookies - -prevent-reading-cookies +kill-popups -send-vanilla-wafer -send-wafer } + In file: default.action [ View ] [ Edit ] + + {-add-header + -block + -content-type-overwrite + -crunch-client-header + -crunch-if-none-match + -crunch-incoming-cookies + -crunch-outgoing-cookies + -crunch-server-header + +deanimate-gifs + -downgrade-http-version + +fast-redirects{check-decoded-url} + +filter{html-annoyances} + +filter{js-annoyances} + +filter{kill-popups} + +filter{webbugs} + +filter{nimda} + +filter{banners-by-size} + +filter{hal} + +filter{fun} + -filter-client-headers + -filter-server-headers + -force-text-mode + -handle-as-empty-document + -handle-as-image + -hide-accept-language + -hide-content-disposition + +hide-forwarded-for-headers + +hide-from-header{block} + +hide-referer{forge} + -hide-user-agent + -inspect-jpegs + +kill-popups + -overwrite-last-modified + +prevent-compression + -redirect + -send-vanilla-wafer + -send-wafer + +session-cookies-only + +set-image-blocker{blank} + -treat-forbidden-connects-like-blocks } / { +block +handle-as-image } @@ -1717,20 +1861,24 @@ CLASS="QUOTE" > is matching "/ads"! But - we did not want this at all! Now we see why we get the blank page. We could - now add a new action below this that explicitly does in our + configuration! But we did not want this at all! Now we see why we get the + blank page. We could now add a new action below this that explicitly + not - block (un blocks ("{-block}") paths with ) paths with + "adsl". There are - various ways to handle such exceptions. Example:
in them (remember, last match in the configuration wins). + There are various ways to handle such exceptions. Example:
"{+filter}" actions. Try - adding the URL for the site to one of aliases that turn off actions. These + tend to be harder to troubleshoot. Try adding the URL for the site to one of + aliases that turn off "+filter":
This would probably be most appropriately put in This would turn off all filtering for that site. This would probably be most + appropriately put in user.action, - for local site exceptions.
, for local site + exceptions. Images that are inexplicably being blocked, may well be hitting the + "+filter{banners-by-size}" rule, which assumes + that images of certain sizes are ad banners (works well most of the time + since these tend to be standardized). PrevHome