.html. Early web servers for Unix used
.html, while early servers for Windows 3.1 were limited to
.htmbecause of the MSDOS three-character extension limit. Modern web servers are configured to accept both. Web browsers, on the other hand, only pay attention to the "content-type" that the server reports, which will be
text/htmlin either case, and essentially ignore the file extension altogether. Consistency can be helpful simply because commands like:
mv *.html /some/other/directorywill reliably move all of your pages, but that is just a convenience for webmasters. There is no fundamental difference between the two.
The really interesting page extensions are
.php, and so on. These are
all ways of enhancing a regular HTML page with commands that
cause the server to insert files at various points, fetch parts
of the page from a database, perform computations and so on.
These are known as "dynamic" web pages. The simplest
.shtml files, which feature
server side include
directives. Almost all web servers support these and they are easy
to learn first.
.asp files are
Active Server Pages,
Microsoft's contribution to this category.
.php files are PHP pages,
which allow pages to be enhanced with the PHP programming language;
as of this writing this is a very popular option. Many other
.shtml files are
HTML containing "server-side include" directives; some servers are
configured to only take up the CPU required to parse the pages that
have a .shtml extension. .php files, similarly, feature PHP directives.
There are many lesser-known dynamic page technologies, most of which have
their own commonly used file extension.
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