.htaccess

A .htaccess (hypertext access) file is a directory-level configuration file supported by several web servers, used for configuration of site-access issues, such as URL redirection, URL shortening, Access-security control (for different webpages and files), and more.

A site could have more than one .htaccess file, and the files are placed inside the web tree (i.e. inside directories and their sub-directories), and hence their other name distributed configuration files.

.htaccess files acts as a subset of the server's global configuration file (like httpd.conf) for the directory that they are in, or all sub-directories.

The original purpose of .htaccess—reflected in its name—was to allow per-directory access control by, for example, requiring a password to access the content. More commonly, however, the .htaccess files define or override many other configuration settings such as content type, character set, CGI handlers, etc.

The 'dot' (period or full stop) before the file name makes it a hidden file in Unix based environments.

.htaccess are written in the Apache Directives variant of the Perl Compatible Regular Expressions (PCRE) language. Learning basic PCRE itself can help in mastering work with these files.

For historical reasons, the format of .htaccess is a limited subset of the Apache HTTP server's global configuration file httpd.conf even when used with web servers such as Oracle iPlanet Web Server and Zeus Web Server which have very different native global configuration files.

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