Htaccess is a very important aspect of any web server’s operations. It is important to distinguish first though that htaccess files work only with the Apache web server. If you are running IIS or LIGHTTPD, then you will not be using htaccess directly, but mimicking the features. Htaccess itself is a very specific set of rules that can be applied to incoming web requests. These rules have a very specific syntax that they are written in, which must be followed directly to achieve the proper effect. The purpose of using htaccess rules are to take an incoming web request and transform or translate it into something different.
A good example of an htaccess use will be for SEO operations. A great deal of websites today are using content management systems. While content management systems are great for making on the fly changes to your website, they are not so friendly when it comes to search engine friendly URLs. For example, you may see the following URL: http://somewebsite.com/page.php=2342343&content=234 The problem with this that the url itself is both long and dynamic. The URL can change, which would cause an previous links to that page to break. With htaccess, you can create a static link to that page. For example, if you have http://somewebsite.com/page.php=2342343&content=234 and http://somewebsite.com/page.php=234232463&content=2532 both going to the same page, you can use htaccess to rewrite those incoming request to http://somewebsite.com/page324.html. This way, you can have more than one link that goes to the same page or content.
Htaccess, while very useful, has a very difficult syntax to properly use. While not being a scripting language, the attention to detail required to be sure that htaccess rules work correctly is very high. The good thing is though, that the results of proper htaccess rules are very rewarding. When using a complicated database driven application for a website, htaccess rules will almost always be required in order to make the pages compliant with search engines. There are some pre-built CMS packages that will generate the correct htaccess rules for you, however, custom applications will require much more attention to detail.