How does .htaccess file work?

Please tell me how does the .htaccess files works.

Thank you,
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basiclifeConnect With a Mentor Commented:
An example of a .htaccess I use:

Options +Indexes
ErrorDocument 404 /index.php?page=404%20Not%20Found
ErrorDocument 401 /index.php?page=401%20Authorisation%20Required
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -l [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^.* - [L]
RewriteRule ^updatecheck/(.*)/(.*)  updatecheck.html?software=$1&ver=$2 [L]
RewriteRule ^openurl/(.*)             openurl.php?url=$1 [L]
RewriteRule ^([a-z]*).html?(.*)      index.php?page=$1&$2                   [L]
RewriteRule ^([a-z]*).html             index.php?page=$1 [L]

From top-down:
Allow indexes (let ppl browse direcotory contents)
Set which pages to redirect to if an HTTP 401 or 404 error occures
The rest is part of mod_rewrite...

It allows me to have a URL of that actually accesses
as well as taking in some variables and passing them to an update check script and another one that opens URLs.

It hides half of what my code does and also makes my pages appear static (like Experts-Exchange! the page you're looking at isn't plain HTML).

static pages are indexed better by search engines. Google for example does not index dynamically generated pages.
That's a wildly extensive topic.  Almost any piece of Apache configuration (there are certainly some exceptions) can go in a .htaccess file.  Google will find hundreds of decent tutorials on using them (the first result for ".htaccess" is here: )

Can you be a little more specific about what you want to know?
One of the most common uses of .htaccess is to hold directives associated with the mod_rewrite module.
As VoteyDisciple points out, this is one of many "complex" topics.

For mod_rewrite, .htaccess is used to contain directives that are specific to the containing directory.

mod_rewrite is frequently used to simplify URI's (i.e., the portion of the URL after the hostname (and optional port number)).

For example, using mod_rewrite, a URL like:


can be transformed to the URL required by the back end:

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