本文引自：http://www.stevenhargrove.com/redirect-web-pages/
The internet today is full of webmasters that are always updating, editing and even deleting web pages.
Lets say you are updating your website completely, changing the names of page's filenames (ex: file.html to file.php) and so on, this is great, you should stay updated! But what if you want to get rid of those old pages without having to worry about those who go to the old web page and see nothing? It doesnt end there either, other visitors do include major search engines such as MSN, Google and Yahoo! If people are finding your old pages when querying in these search engines, and they attempt to go to that page that has been deleted or moved, they will get a "404 File Not Found" Error! Now i know you dont want that, no webmaster wants that!
UPDATE: For those of you still confused on what web page redirection is, I have written a follow-up article titled Understanding Web Page Redirection, the smart way, to help answer some of the questions I most commonly get in the comments of this article.
The 301 Redirect
The best way to redirect those pages is by using something called a "301 Redirect". What this 301 redirect does, is it blatantly redirects to a different page when it is triggered. What makes the 301 redirect the best? Not only does it accomplish your redirect - it does it safely. No having to worry about the search engines penalizing you for it. To be specific, the 301 redirect tells the browser, or in other cases, it tells the search engines "Hey this page has been moved, here is the correct URL!". Think of it as you getting mail that is not addressed to your name. Possibly addressed to somebody who has lived there prior to yourself. What do you do? You tell the post man (or woman) "Hey they don't live here anymore, here is the correct address". It is the same concept, pretty simple stuff.
So lets get started. Below you will see several methods of using the 301 redirect, including the redirect in PHP, the redirect in ASP, the redirect in ASP .NET, the redirect in JSP (JAVA), the redirect in IIS, the redirect in ColdFusion, the redirect in CGI/PERL and finally the one I find most useful, the redirect using htaccess. Also showing other useful ways of using the 301 redirect with mod_rewrite!
HTML Redirection
How do you redirect using html you ask? Here is how: DONT!
Over the past 8-10 years, use of meta tag refresh redirection has been abused for uses in relation to SPAM. The result of this and other scenarios of mis-uses of it, is that when using it, that page WILL be de-indexed from every search engine.
NOTE: This also applies to javascript redirection. Search engines can easily detect javascript and meta tag redirection, so just dont do it, use the 301 redirect.
Now, this doesn't necessarily apply to *everything*. If it is used properly, then you have nothing to worry about. For example, often on many forum engines - you will see when you perform different tasks such as making a thread, replying to one or even things like logging in - you will notice it takes you to a "please wait a moment" screen. On those types of pages, they are using either javascript or meta tag redirection, and its perfectly legit.
Canonical Links
My first impression of canonical links is "Great, but where the hell were you 10 years ago?". That aside, from what I see they really are for one purpose: dynamic content.
To put that into perspective, I have a wordpress plugin on this blog that will separate my comments onto multiple pages, so I don't have to show 500+ comments on one single page. So it paginates the comments for me.
The slight drawback to this, is that since it is paginating my comments onto several pages - this exact article data exists on those pages as well. So those page url's end up looking like this: http://www.stevenhargrove.com/redirect-web-pages/comment-page-50/. When really, it is just the same page with different comments.
Using canonical links, I could specify in the of the html document my canonical link. Which would look like this:
HTML:
<link rel="canonical" href="http://www.stevenhargrove.com/redirect-web-pages/" />
Another interesting bit to consider about canonical links:
Can this link tag be used to suggest a canonical URL on a completely different domain?
No. To migrate to a completely different domain, permanent (301) redirects are more appropriate. Google currently will take canonicalization suggestions into account across subdomains (or within a domain), but not across domains. So site owners can suggest www.example.com vs. example.com vs. help.example.com, but not example.com vs. example-widgets.com.
Matt Cutts has a great article that shows how to use these more in depth. He also has a slide show that covers it a bit.
301 Redirect Using htaccess
Using htaccess to accomplish the 301 redirect is highly suggested due to it being fairly convenient to manage, rather than setting redirects on each individual page, you can simply add the redirect code to the .htaccess file.
Here is how to do it:
1. Create a file on the root directory of your website, name it ".htaccess".
2. Open the .htaccess file using notepad or what ever text editor that you prefer.
3. Add this into the .htaccess file, save it and then upload it to your web server:
Redirect 301 /old/old.html http://www.you.com/new.html
NOTE: Don't add "http://www" to the first part of the statement - place the path from the top level of your site to the page. Also ensure that you leave a single space between these elements:
redirect 301 (the instruction that the page has moved)
/old/old.html (the original folder path and file name)
http://www.you.com/new.html (new path and file name)
Also note that you are not required to redirect the page to another domain, an equally useful purpose for using the 301 redirect, is redirecting old pages to the new pages on the same domain, it all works the same way!
UPDATE: .htaccess Editor is a simple, yet useful resource for generating htaccess files.
301 Redirect Using Mod_Rewrite
Mod_Rewrite has got to be one of the most usefull modules a server can have in terms of SEO, it allows to organize the file structure of your web site in a dynamic yet simple fashion, in this example I show a useful method of 301 redirecting with mod_rewrite.
When somebody links to your website, sometimes they dont always link to you in the way that you want them to. If somebody links to www.yoursite.com and somebody else links to yoursite.com, Google will assign a separate pagerank for each of those. Yes, it is stupid but it is true, by inserting the below example into your .htaccess file, it will solve the problem by redirecting anything linking to yoursite.com to www.yoursite.com, also redirecting the pagerank, so no worries!
RewriteEngine On
rewritecond %{http_host} ^yoursite.com
rewriteRule ^(.*) http://www.yoursite.com/$1 [R=301,L]301 Redirect Using IIS
1. In internet services manager, right click on the file or folder you wish to redirect.
2. Select the radio titled "a redirection to a URL".
3. Enter the page that the page will be redirected to.
4. Check "The exact url entered above" and the "A permanent redirection for this resource".
5. Click on 'Apply'.
301 Redirect Using ColdFusion
As well as many server side scripting languages, using the 301 redirect in them is fairly simple.
Simply add this code to your ColdFusion page:
<cfheader statuscode="301" statustext="Moved permanently"> <cfheader name="Location" value="http://www.new-url.com/">
301 Redirect Using PHP
Simply add this code to your page or script:
<? header( "HTTP/1.1 301 Moved Permanently" ); header( "Status: 301 Moved Permanently" ); header( "Location: http://www.new-url.com/" ); exit(0); // This is Optional but suggested, to avoid any accidental output ?>
301 Redirect Using ASP
Simply add this code to your page or script:
<%@ Language=VBScript %> <% Response.Status="301 Moved Permanently" Response.AddHeader "Location", "http://www.new-url.com/" %>
301 Redirect Using ASP .NET
Simply add this code to your page or script:
<script runat="server">
private void Page_Load(object sender, System.EventArgs e)
{
Response.Status = "301 Moved Permanently";
Response.AddHeader("Location","http://www.new-url.com/");
}
</script>301 Redirect Using JSP/JAVA
Simply add this code to your page or script:
<% response.setStatus(301); response.setHeader( "Location", "http://www.new-url.com/" ); response.setHeader( "Connection", "close" ); %>
301 Redirect Using CGI/PERL
Simply add this code to your cgi/perl script:
$q = new CGI;
print $q->redirect(" http://www.new-url.com/ ");301 Redirect Using Ruby/Ruby on Rails
Simply add this code to your ruby/ruby on rails script:
head :moved_permanently, :location => "http://www.domain.com/
Zachary Pinter has a nice explanation of this.
Pleaee note that all of the snippets of code above are examples and I have tested each at some point. However, I am in no way responsible for any damage the code may cause, you use this code at your own risk.