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MOD_REWRITE_for_Dummies
| MOD_REWRITE for Dummies
A short article in human language
This article is not a complete quide to Apache's mod_rewtite
neither to .htaccess. Its purpose is to help you - the webmaster
- to create "mod_rewriten" versions of your dynamic webpages
even if you have limited technical knowledge. I won't show you
all the tips-and-tricks - my aim is to bring all the complexity
of the Apache's documentation to 1-2 pages of human lanuage -
easy and fast.
What is mod_rewrie?
Mod_rewrite is Apache extension which allows you to "rewrite"
the URLs of your web pages. If your server supports this
technology (most linux webhosts do nowadays) you are able to
rewrite virtually any URL into anything you like. Most often it
is used to rewrite the URLs of dynamicly generated webpages such
as www.mywebsite.com/index.php?par1=1&par2=2&par3=2... This can
easy be 'translated' into www.mywebsite.com/par1/par2/par3
Why mod_rewrite?
- Search engine optimization - there are a lot of debates on
this topic, but it is still true that the static-looking links
rank better than the dynamic ones. Here is a comfirmation from
Google on that topic:
"Your pages are dynamically generated. We're able to index
dynamically generated pages. However, because our web crawler
could overwhelm and crash sites that serve dynamic content, we
limit the number of dynamic pages we index. In addition, our
crawlers may suspect that a URL with many dynamic parameters
might be the same page as another URL with different parameters.
For that reason, we recommend using fewer parameters if
possible. Typically, URLs with 1-2 parameters are more easily
crawlable than those with many parameters."
- User-friendlyness - Some users remember the URLs visally. Even
if they bookmark, they can easier recognize a link like
www.mywebsite.com/services.html than
www.mywebsite.com/index.php?task=12 for example.
- Security - mod_rewrite helps you hide the parametters passed
in the application. Basicly your dynamic pages should be secure
enough even without mod_rewrite. But hiding the parametters will
decrease the danger of attack
How to use it? Mod_rewrite is really powerful if you are
familiar with the regular expressions which it uses. But
learning the whole pattern syntax can be quite complicated,
especially for the non-technical user. Thats why i'll teach you
at several simple patterns which are pretty enough to get your
website URLs rewritten.
Lets start: First you need to create a file called .htaccess and
place it exactly in the folder where you want the rewriting to
take effect (it will also take effect over all subfolders). In
case you already have a .htaccess file you can simply add the
lines to it (if it already has mode_rewrite directives you can
mess them however). Open it in a simple text editor an start
with:
Options +FollowSymLinks RewriteEngine on
Now the rewrite engine is switched on. You can now start adding
as many rewrite rules as you want. The format is simple:
RewriteRule rewrite_from rewrite_to
Here "RewriteRule" is static text, i.e. you should not change.
"rewrite_from" is the address which will be typed in the browser
and "rewrite_to" - which page the server will actually activate.
Both of these can contain "masks", but in "rewrite_to" we will
only use $ and will discuss more or "rewrite_from" part. Let me
"meet you" with the very few masks you'll need and bring you
some samples. You'll see how easy is it.
Let's stop talking theory and see an example. Let's imagine your
server runs an e-shop, which uses URLs like
index.php?task=categories to list the categories,
index.php?task=category&id=5 to show a category contents and
other parametters in 'task' to do other things.
RewriteRule ^(.*).html index.php?task=$1
What does all that mean? This is a rewrite rule which allows you
to make your URLs looking as "static". In this example
categories.html will be "translated" to
index.php?task=categories. So you no longer need dynamic URL to
list ther categories, but can write categories.html
But what do all these strange characters mean? - ^ character
marks the beginning. I.e. you tell the server that it should not
expect anything before it. - (.*) - This combination is the most
often used and it means literally "everything". So everything
you type before ".html" (i.e. your fake file name) will be
passed as: - $1 - This is a parametter, saying where the first
mask should be put. If you have more than one masks (masks are
everything which you use to represent dynamich text or file
names) you can use $2, $3 etc. You'll seemor ein the following
examples.
So, if you have categories.html it will be translated info
index.php?task=categories, services.html into
index.php?task=services etc...
What if you have more than one parametter? First, you should use
some characters as delimiter:
RewriteRule ^(.*)-(.*).html index.php?task=$1&language=$2
Here how you can also pass task and language. For example:
categories-englist.html will be translated into
index.php?task=categories&language=english.
IMPORTANT: If you first write RewriteRule ^(.*).html
index.php?task=$1 The second one may not work. You need to
always start from the most complicated rule to the simplest one.
Make it Better: The rule (.*) is too general and often may
prevent you of making more complicated rewriting rules. So it is
recommended that you "limit" the rules into something more
concrete. Here are a couple of advices:
- Use the "OR" operator. In our e-shop example we have only few
possible "tasks" passed to index.php. Lets say:
index.php?task=categories index.php?task=category
index.php?task=product index.php?task=services
What will happen if you want to use your static file about.html?
It will be rewritten into index.php?task=about and won't work.
So you can use the OR operator and limit the rewriting only to
the cases you need:
RewriteRule ^(categories|category|product|services).html
index.php?task=$1
This tells the server to rewrite only if the file name is
categories.html OR category.html OR product.html OR services.html
- Using "numbers". You can easy limit the rewriter to rewrite if
it meets only numbers at a certain place:
RewriteRule ^category-([0-9]*).html index.php?task=category&id=$1
With ([0-9]*) mask you tell the rewrite engine that on the mask
place it should expect onlly numbers. So if it see
category-english.html it won't rewrite to
index.php?task=category&id=english, but to
index.php?task=category&language=english (because of the rule we
have shown above - RewriteRule ^(.*)-(.*).html
index.php?task=$1&language=$2.).
Complete example: Here is how will look the final .htaccess file
for our imaginary e-shop:
-------- Options +FollowSymLinks RewriteEngine on
RewriteRule ^(.*)-(.*).html index.php?task=$1&language=$2.
RewriteRule ^(categories|category|product|services).html
index.php?task=$1 RewriteRule ^category-([0-9]*).html
index.php?task=category&id=$1
About the author:
The author is Senior Deveoper in PIM Team Bulgaria and Consultant in SEO PIM Team
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