PHP—Retrieving System Information

The web server provides environmental variables, which can be accessed by PHP programs. PHP provides a function, getenv(), which, as its name suggests, gets environmental variables. For example,

getenv(REMOTE_ADDR)

returns the IP address of whoever is viewing the PHP document. You could use that value by assigning it to your own variable (e.g., IP_address) and then doing something with that value (for example, echoing it):

$IP_address = getenv(REMOTE_ADDR);

echo "Your IP Address is $IP_address";

Here is a list of common system variables and what information they provide:

• HTTP_ACCEPT - types of documents the web browser can interpret, e.g., images, Word documents, sound clips
  
  
• HTTP_USER_AGENT - type of web browser (both Microsoft Internet Explorer and Netscape Navigator indicate "Mozilla," although Internet Explorer also includes "MSIE")
  
  
• PATH_INFO - the directory where the web page is located, as seen by the client
  
  
• PATH_TRANSLATED - the actual directory where the web page is located on the server
  
  
• QUERY_STRING - text following a question mark (?) after the web address (e.g., "http://www.website.org/search.php?dinosaur"); indicates an argument to passed to the PHP program, such as a search term
  
  
• REMOTE_ADDR - The IP address of the client requesting the web page
  
  
• SCRIPT_NAME - the name of the "scripting software," in this case, PHP
  
  
• SERVER_NAME - the name of the web server
  
  
• SERVER_PROTOCOL - the protocol used (usually HTTP:)
  
  
• SERVER_SOFTWARE - the software run by the web server

Next (Manipulating Variables)