$_SERVER['PHP_SELF']

The filename of the currently executing script, relative to the document root. For instance, $_SERVER['PHP_SELF'] in a script at the address http://example.com/test.php/foo.bar would be /test.php/foo.bar. The __FILE__ constant contains the full path and filename of the current (i.e. included) file.

If PHP is running as a command-line processor this variable contains the script name since PHP 4.3.0. Previously it was not available.
$_SERVER['QUERY_STRING']

The query string, if any, via which the page was accessed.
$_SERVER['SCRIPT_FILENAME']

The absolute pathname of the currently executing script.

Note: If a script is executed with the CLI, as a relative path, such as file.php or ../file.php, $_SERVER['SCRIPT_FILENAME'] will contain the relative path specified by the user.
$_SERVER['PATH_TRANSLATED']

Filesystem- (not document root-) based path to the current script, after the server has done any virtual-to-real mapping.

Note: As of PHP 4.3.2, PATH_TRANSLATED is no longer set implicitly under the Apache 2 SAPI in contrast to the situation in Apache 1, where it’s set to the same value as the SCRIPT_FILENAME server variable when it’s not populated by Apache. This change was made to comply with the CGI specification that PATH_TRANSLATED should only exist if PATH_INFO is defined.

Apache 2 users may use AcceptPathInfo = On inside httpd.conf to define PATH_INFO.
$_SERVER['SCRIPT_NAME']

Contains the current script’s path. This is useful for pages which need to point to themselves. The __FILE__ constant contains the full path and filename of the current (i.e. included) file.

$_SERVER['REQUEST_URI']

The URI used to access this page; for instance, ‘/index.html’. Includes the query string.

__FILE__
The full path and filename of the file. If used inside an include, the name of the included file is returned. Since PHP 4.0.2, __FILE__ always contains an absolute path whereas in older versions it contained relative path under some circumstances.

* __FILE__ returns the filename of the script that is currently being run.
* dirname returns the directory of a given filename
* basename() returms the filename component of path. To put it better: it strips any “parent” directories off a given string.

Example: Suppose you run /home/httpd/html/index.php, which contains

Now __FILE__ gives “/home/httpd/html/index.php”, dirname(__FILE__) gives “/home/httpd/html” and basename(dirname(__FILE__)) gives “html”. So basename() stripped the “parent” directory “/home/httpd/” off the string “/home/httpd/html”. Don’t be confused of the fact that /home/httpd/html is a directory, but basename is supposed to operate on “filenames”. Internally, a directory is just another file, so a directory name is treated like a filename.

<?php
header("content-type:text/plain");

$keys = array(
    "PATH_INFO",
    "PATH_TRANSLATED",
    "PHP_SELF",
    "REQUEST_URI",
    "SCRIPT_FILENAME",
    "SCRIPT_NAME",
    "QUERY_STRING"
);

$info_row = "<tr><td>$_SERVER[SERVER_SOFTWARE]</td><td></td><td></td>\n";
print "Path Information for $_SERVER[SERVER_SOFTWARE]\n\n";

foreach($keys as $key) {
    print '$_SERVER["'.$key.'"] = '.$_SERVER[$key]."\n";
    $info_row .= "<td>$_SERVER[$key]</td>\n";
}

print '__FILE__ = '. __FILE__;
$info_row .= "<td>".__FILE__."</td>\n</tr>";

print "\n\n\n" . $info_row;
?>