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Friday, April 18, 2008

Introduction to PHP Part III

Please read the post Introduction to PHP, How to Insert Dynamic Content on WebPages, if you haven’t already.

Below is the code snippet from the previous post.


  <html>
  <body>
  Date: <?php echo date("H:i A, jS F Y"); ?>
  </body>
  </html>

I’d like to state the following regarding the above code:

  1. PHP code starts with a <?php and ends with a ?> tag. Though PHP supports some other tags (depending on the configuration) which signify the same but these are the most widely used and are guaranteed to work on most servers.

  2. You can have any number of <?php …?> blocks in a file.

  3. In PHP too, like C++ comments are written using // (single line) and /*…*/ (multi-line) symbols. Besides these one more symbol i.e. ‘#’ symbol can also be used for single line comments.

  4. [Update: Added this point] Each statement of PHP ends with a semicolon ";" just like in C++. [/Update]

  5. No need to bother about the arguments passed to the date() function now, it is just a format string which tells the date function which format to return the date in. eg. “H:i A, jS F Y” tells the date function to return date and time as “06:00 AM, 18th April 2008”. Echo command just echoes (prints) it to the screen.

  6. Files containing PHP codes must have a “.php” extension (default) even if it contains HTML too.

  7. Any file having an extension “.php” is parsed by PHP. As someone requests a PHP page, the server hands it over to PHP parser. PHP parses the file returning HTML codes as it is, but when it finds a <?php…?> block, it interprets the code between the tags and returns the result back. So we get something like this upon parsing the PHP code at the top of this post:

    
      <html>
      <body>
      Date: 06:00 AM, 18th April 2008
      </body>
      </html>
    
    

    In this case, line 1 and 2 were returned as is without any interpretation whereas the PHP code between <?php…?> were interpreted and results were returned. Again line 4 and 5 were returned the same.

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