.htm, .html, and .shtml are all file extensions used for web pages, but they have slight differences related to how the server handles them:
-
.htm and .html: These are essentially identical and the most common file extensions for web pages. They contain HTML (HyperText Markup Language) code, which defines the structure and content of a web page. The difference in length is a historical artifact from older systems with file name limitations (like DOS's 8.3 filename limit). Today, there's no practical difference, and
.htmlis generally preferred due to being more explicit. Servers treat both extensions the same way: they simply send the HTML code to the user's browser for rendering. -
.shtml: This extension stands for Server-Parsed HTML. It indicates that the web server should process the file before sending it to the browser. This processing typically involves Server-Side Includes (SSI). SSI are directives embedded within the HTML code that tell the server to perform certain actions, such as:
- Including other files: This is useful for things like headers, footers, and navigation menus that are common across multiple pages. Instead of repeating the same code on every page, you can store it in a separate file and include it using SSI.
- Executing external programs: This allows you to generate dynamic content on the server-side, such as displaying the current date and time or the results of a database query.
- Setting environment variables: These can be used to control the behavior of the server or other SSI directives.
The key difference is that .htm and .html files are static, meaning their content is fixed when they are sent to the browser. .shtml files, on the other hand, can be dynamic, as the server can modify their content before sending them. However, with the advent of more powerful server-side technologies like PHP, Python (with frameworks like Django and Flask), Node.js, Ruby on Rails, and others, the use of SSI and .shtml has significantly declined. These newer technologies offer more flexibility and power for creating dynamic web pages.
In summary:
| Extension | Description | Server Processing | Dynamic Content |
|---|---|---|---|
.htm |
HTML file | None | No |
.html |
HTML file (preferred) | None | No |
.shtml |
Server-Parsed HTML (SSI) | Yes | Potentially Yes |
If you're building a modern website, you'll likely use .html and a more robust server-side technology for dynamic content rather than .shtml.