As long as allow_url_fopen is enabled in php.ini, you can use HTTP and FTP URLs with most of the functions that take a filename as a parameter. In addition, URLs can be used with the include, include_once, require and require_once statements (allow_url_include must be enabled for these). See Supported Protocols and Wrappers for more information about the protocols supported by PHP.
For example, you can use this to open a file on a remote web server, parse the output for the data you want, and then use that data in a database query, or simply to output it in a style matching the rest of your website.
Example #1 Getting the title of a remote page
<?php
$file = fopen ("http://www.example.com/", "r");
if (!$file) {
echo "<p>Unable to open remote file.\n";
exit;
}
while (!feof ($file)) {
$line = fgets ($file, 1024);
/* This only works if the title and its tags are on one line */
if (preg_match ("@\<title\>(.*)\</title\>@i", $line, $out)) {
$title = $out[1];
break;
}
}
fclose($file);
?>
You can also write to files on an FTP server (provided that you have connected as a user with the correct access rights). You can only create new files using this method; if you try to overwrite a file that already exists, the fopen() call will fail.
To connect as a user other than 'anonymous', you need to specify
the username (and possibly password) within the URL, such as
'ftp://user:password@ftp.example.com/path/to/file'.
(You can use the same sort of syntax to access files via
HTTP when they require Basic authentication.)
Example #2 Storing data on a remote server
<?php
$file = fopen ("ftp://ftp.example.com/incoming/outputfile", "w");
if (!$file) {
echo "<p>Unable to open remote file for writing.\n";
exit;
}
/* Write the data here. */
fwrite ($file, $_SERVER['HTTP_USER_AGENT'] . "\n");
fclose ($file);
?>
Note:
You might get the idea from the example above that you can use this technique to write to a remote log file. Unfortunately that would not work because the fopen() call will fail if the remote file already exists. To do distributed logging like that, you should take a look at syslog().