PHP provides access to a number of predefined functions and variables.<\/p>\n
For an exhaustive overview of the predefined variables available in the PHP programming language please check out the related section on php.net website<\/a>, from which the following complete list was derived.<\/p>\n Superglobals \u2014 Superglobals are built-in variables that are always available in all scopes In this section we focus on a couple of those built-in variables that we may use in our scripts. In particular we will see how the $_SERVER array<\/strong> provides access to information on our working environment and we will just hint, for now, at the $_POST array<\/strong>, that let us retrieve data submitted by website visitors through web forms, an essential bit of the web applications that we will build later on.<\/p>\n The $_SERVER variable, an array with several predefined keys, provides access to many so called “environmental” variables about our working environment and our website visitors.<\/p>\n To check all available keys for the $_SERVER array, we can use the array_keys() function that we have introduced in the previous section about PHP arrays basics<\/a>.<\/p>\n At the time of this writing, the code above will output the following result on our test Linux server:<\/p>\n
\n$GLOBALS \u2014 References all variables available in global scope
\n$_SERVER \u2014 Server and execution environment information
\n$_GET \u2014 HTTP GET variables
\n$_POST \u2014 HTTP POST variables
\n$_FILES \u2014 HTTP File Upload variables
\n$_REQUEST \u2014 HTTP Request variables
\n$_SESSION \u2014 Session variables
\n$_ENV \u2014 Environment variables
\n$_COOKIE \u2014 HTTP Cookies
\n$php_errormsg \u2014 The previous error message
\n$HTTP_RAW_POST_DATA \u2014 Raw POST data
\n$http_response_header \u2014 HTTP response headers
\n$argc \u2014 The number of arguments passed to script
\n$argv \u2014 Array of arguments passed to script\n<\/p><\/div>\nThe $_SERVER variable<\/h2>\n
\r\n\\n\"; \r\n\r\nforeach($server_array_keys as $key){\r\n echo \"
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