Tuesday 28th of February 2017 08:35:48 AM

Module Rewrite - URL Rewriting Guide

  • Protecting your images and files from linking
  • degrades even further when colors are printed, since factors asdiverse as the stock and color of the paper used, and even thetemperature of the printing mechanism, can affect how well colors arereproduced on paper.

    In effect, this is yet anotherarea where you must remember that total control over documentappearance is simply not possible. In this case, it's due to acombination of inconsistent operating system settings and thevagaries of human perception, which is an obstacle no computer isgoing to overcome any time soon.

  • Redirect visitor by domain name
  • Redirect domains to other directory
  • Redirect visitor by user agent

  • top
    Module Rewrite

    Welcome to mod_rewrite, voodoo of URL manipulation.

    This document describes how one can use Apache's mod_rewrite to solve typical URL based problems webmasters are usually confronted with in practice. The Apache module mod_rewrite is a module which provides a powerful way to do URL manipulations. With it you can nearly do all types of URL manipulations you ever dreamed about. The price you have to pay is to accept complexity, because mod_rewrite is not easy to understand and use for the beginner.

    NOTE: Depending on your server configuration it can be necessary to change the examples for your situation. Always try to understand what it really does before you use it. Bad use would lead to deadloops and will hang the server.

    The most example's can be used in the .htaccess file while other ones only in the Apache htppd.conf file.


    top
    RewriteCond

    The RewriteCond directive defines a rule condition. Preserve a RewriteRule with one or more RewriteCond directives. The following rewriting rule is only used if its pattern matches the current state of the URI and if these additional conditions apply too.

    You can set special flags for condition pattern by appending a third argument to the RewriteCond directive. Flags is a comma-separated list of the following flags:

    [NC] (No Case)
    This makes the condition pattern case insensitive, no difference between 'A-Z' and 'a-z'.

    [OR] (OR next condition)
    Used to combinate rule conditions with a OR.


    top
    RewriteRule

    The RewriteRule directive is the real rewriting.

    You can set special flags for condition pattern by appending a third argument to the RewriteCond directive. Flags is a comma-separated list of the following flags:

    [R] (force Redirect)
    Redirect the URL to a external redirection. Send the HTTP response, 302 (MOVED TEMPORARILY).

    [F] (force URL to be Forbidden)
    Forces the current URL to be forbidden. Send the HTTP response, 403 (FORBIDDEN).

    [G] (force URL to be Gone)
    Forces the current URL to be gone. Send the HTTP response, 410 (GONE).

    [L] (last rule)
    Forces the rewriting processing to stop here and don't apply any more rewriting rules.

    [P] (force proxy)
    This flag forces the current URL as a proxy request and put through the proxy module mod_proxy.


    top
    Regular expressions

    Some hints about the syntax of regular expressions:

    Text:
    . Any single character
    [chars] One  of chars
    [^chars] None of chars
    text1|text2 text1 or text2
    
    Quantifiers:
    ? 0 or 1 of the preceding text
    * 0 or N of the preceding text (N > 0)
    + 1 or N of the preceding text (N > 1)
    
    Grouping:
    (text) Grouping of text
    
    Anchors:
    ^ Start of line anchor
    $ End of line anchor
    
    Escaping:
    \ char escape that particular char
    

    top
    Condition pattern

    There are some special variants of CondPatterns. Instead of real regular expression strings you can also use one of the following:

    < Condition (is lower than Condition)
    Treats the Condition as a string and compares it to String. True if String is lower than Condition.

    > Condition (is greater than Condition)
    Treats the Condition as a string and compares it to String. True if String is greater than CondPattern.

    = Condition (is equal to Condition)
    Treats the Condition as a string and compares it to String. True if String is equal to CondPattern.

    -d (is directory)
    Treats the String as a pathname and tests if it exists and is a directory.

    -f (is regular file)
    Treats the String as a pathname and tests if it exists and is a regular file.

    -s (is regular file with size)
    Treats the String as a pathname and tests if it exists and is a regular file with size greater than zero.

    -l (is symbolic link)
    Treats the String as a pathname and tests if it exists and is a symbolic link.

    -F (is existing file via sub request)
    Checks if String is a valid file and accessible via all the server's currently configured access controls for that path. Use it with care because it decreases your servers performance!

    -U (is existing URL via sub request)
    Checks if String is a valid URL and accessible via all the server's currently configured access controls for that path. Use it with care because it decreases your servers performance!

    NOTE: You can prefix the pattern string with a '!' character (exclamation mark) to specify a non-matching pattern.


    top
    Protecting your images and files from linking

    DESCRIPTION: In some cases other webmasters are linking to your download files or using images, hosted on your server as inline-images on their pages.

    RewriteEngine On
    RewriteCond %{HTTP_REFERER} !^$ [NC]
    RewriteCond %{HTTP_REFERER} !^http://domain.com [NC]
    RewriteCond %{HTTP_REFERER} !^http://www.domain.com [NC]
    RewriteCond %{HTTP_REFERER} !^http://212.204.218.80 [NC]
    RewriteRule ^.*$ http://www.domain.com/ [R,L]
    

    EXPLAIN: In this case are the visitors redirect to http://www.domain.com/ if the hyperlink has not arrived from http://domain.com, http://www.domain.com or http://212.204.218.80.


    top
    Redirect visitor by domain name

    DESCRIPTION: In some cases the same web site is accessible by different addresses, like domain.com, www.domain.com, www.domain2.com and we want to redirect it to one address.

    RewriteEngine On
    RewriteCond %{HTTP_HOST} !^www.domain.com$ [NC]
    RewriteRule ^(.*)$ http://www.domain.com/$1 [R,L]
    

    EXPLAIN: In this case the requested URL http://domain.com/foo.html would redirected to the URL http://www.domain.com/foo.html.


    top
    Redirect domains to other directory
    RewriteEngine On
    RewriteCond %{HTTP_HOST} ^www.domain.com$
    RewriteCond %{REQUEST_URI} !^/HTML2/
    RewriteRule ^(.*)$ /HTML2/$1
    

    top
    Redirect visitor by user agent

    DESCRIPTION: For important top level pages it is sometimes necesarry to provide pages dependend on the browser. One has to provide a version for the latest Netscape, a version for the latest Internet Explorer, a version for the Lynx or old browsers and a average feature version for all others.

    # MS Internet Explorer - Mozilla v4
    RewriteEngine On
    RewriteCond %{HTTP_USER_AGENT} ^Mozilla/4(.*)MSIE
    RewriteRule ^index\.html$ /index.IE.html [L]
    # Netscape v6.+ - Mozilla v5
    RewriteCond %{HTTP_USER_AGENT} ^Mozilla/5(.*)Gecko
    RewriteRule ^index\.html$ /index.NS5.html [L]
    # Lynx or Mozilla v1/2
    RewriteCond %{HTTP_USER_AGENT} ^Lynx/ [OR]
    RewriteCond %{HTTP_USER_AGENT} ^Mozilla/[12]
    RewriteRule ^index\.html$ /index.20.html [L]
    # All other browsers
    RewriteRule ^index\.html$ /index.32.html [L]
    

    EXPLAIN: In this case we have to act on the HTTP header User-Agent. If the User-Agent begins with Mozilla/4 and is MS Internet Explorer (MSIE), the page index.html is rewritten to index.IE.html and the rewriting stops. If the User-Agent begins with Mozilla/5 and is Netscape (Gecko), the page index.html is rewritten to index.NS5.html. If the User-Agent begins with Lynx/ or Mozilla/1,2, the page index.html is rewritten to index.20.html. All other browsers receive page index.32.html


        
































    floated to the left, and the second to the right. This rule preventsthe second image from overlapping the first by 100 pixels. Instead,the second image is forced down until its top is below the bottom ofthe left-floated image, as depicted in Figure 8-32.

    Figure 8-32

    Figure 8-32. More overlap prevention

    4. A floating element's top may not be higher thanthe inner top of its parent.

    Another simple rule. This one keeps floating elements from floating needed to be relatively dark. Not so with CSS; all you need to do is add a class to all anchors that need to be this shade of gray and modify your styles accordingly, with the result seen in Figure 6-4:

    BODY {color: black;}
    A:link {color: #808080;}      /* medium gray */
    A.external:link  {color: silver;}
    A:active {color: silver;}
    A:visited {color: #333333;}   /* a very dark gray */
    Figure 6-4

    Figure 6-4. Changing colors of hyperlinks

    its parent element. This is likely to be BODY,DIV, or another TABLE. Thus, ifan image has a border, and the BODY is its parent,given this rule:

    BODY {color: purple;}

    then, by default, the border around the image will be purple. Ofcourse, to get that border to appear, you have to do a little workfirst.

    Figure 8-51

    Figure 8-51. Stacking the line boxes together

    Then the top of the line box is placed against the bottom of the line box for the preceding line. This will give us a paragraph as shown in Figure 8-52.

    Figure 8-52

    Figure 8-52. The final paragraph of stacked line boxes

    As we can see, the middle line is taller than the other two, but it still isn't big enough to contain the text within it. That's because the position of the inline boxes in the line

    5.4. Styles and Variants

    In comparison with everything that's gone before, this section is practically a no-brainer. The properties discussed herein are so straightforward, and the complexities so minimal, that this will probably all come as a great relief. First we'll talk about font-style, and then move on to font-variant before wrapping up the font properties.