Page 532 - Beginning PHP 5.3

Part III: Using PHP in Practice
header() is very useful if your PHP script needs to send anything other than an HTML Web page. For
example, say you have a report.pdf file on the Web server, and you want to send this to the browser.
You could write the following:

< ?php
header( “Content-Type: application/pdf” );
readfile( “report.pdf” );
? >

The first line tells the Web browser to expect a PDF document rather than a regular Web page. The
second line reads the PDF file on the server ’ s hard drive and outputs its contents to the Web browser,
which can then save or display the PDF.
Usually it ’ s up to the browser as to whether it displays the file in the browser itself, or offers to save it to
the user ’ s hard disk. You can use a Content - Disposition: Attachment header to suggest to the
browser that the file should be saved rather than displayed and, optionally, to suggest a filename for the
saved file:
< ?php
header( “Content-Type: application/pdf” );
header( ‘Content-Disposition: attachment; filename=”Latest Report.pdf”’ );
readfile( “report.pdf” );
? >

By the way, you need to make sure you don ’ t send anything to the browser before calling header() .
This includes HTML markup, or even blank lines, before your opening < ?php tag. This is because, once
PHP has received a request to send some content to the browser, it sends the HTTP headers first (because
the headers need to be sent at the start of the response). Therefore, by the time your header() call is
executed, the content is already being sent, and it ’ s too late to send any more headers. (If you fall foul of

this, then your header isn ’ t sent and PHP generates a Cannot modify header information -
headers already sent warning.)

Getting Information from the Web Server

Each time a PHP script is run, the Web server software makes a wealth of useful information available to
the PHP engine. Such information includes details about the server itself, as well as details of the script
being executed, and many of the HTTP request headers discussed previously in this chapter.
You can access all of this information in your PHP script through the $_SERVER superglobal array. For
example, to display the IP address of the visitor ’ s computer (or proxy server) you might use:

echo “Your IP address is: “ . $_SERVER[“REMOTE_ADDR”];
Because Web servers come in all shapes and sizes, the information available depends very much on your
particular server setup. Having said that, there ’ s usually a core list of values that are always present.
Here ’ s a list of the more common and useful $_SERVER variables:

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