When a file is included, the code it contains inherits the variable scope of the line on which the include occurs. Any variables available at that line in the calling file will be available within the called file, from that point forward.

include()

Files are included based on the file path given or, if none is given, the include path specified. The include() construct will emit a warning if it cannot find a file; this is different behavior from require(), which will emit a fatal error.

If a path is defined (full or relative), the include path will be ignored altogether. For example, if a filename begins with ../, the parser will look in the parent directory to find the requested file.

For more information on how PHP handles including files and the include path, see the documentation for include path.

Example #1 Basic include() example

vars.php
<?php

$color = 'green';
$fruit = 'apple';

?>

test.php
<?php

echo "A $color $fruit"; // A

include 'vars.php';

echo "A $color $fruit"; // A green apple

?>

If the include occurs inside a function within the calling file, then all of the code contained in the called file will behave as though it had been defined inside that function. So, it will follow the variable scope of that function. An exception to this rule are magic constants which are evaluated by the parser before the include occurs.

Example #2 Including within functions

<?php

function foo()
{
    global $color;

    include 'vars.php';

    echo "A $color $fruit";
}

/* vars.php is in the scope of foo() so     *
* $fruit is NOT available outside of this  *
* scope.  $color is because we declared it *
* as global.                               */

foo();                    // A green apple
echo "A $color $fruit";   // A green

?>

When a file is included, parsing drops out of PHP mode and into HTML mode at the beginning of the target file, and resumes again at the end. For this reason, any code inside the target file which should be executed as PHP code must be enclosed within valid PHP start and end tags.

If "URL fopen wrappers" are enabled in PHP (which they are in the default configuration), you can specify the file to be included using a URL (via HTTP or other supported wrapper. If the target server interprets the target file as PHP code, variables may be passed to the included file using a URL request string as used with HTTP GET. This is not strictly speaking the same thing as including the file and having it inherit the parent file's variable scope; the script is actually being run on the remote server and the result is then being included into the local script.

Example #3 include() through HTTP

<?php

/* This example assumes that www.example.com is configured to parse .php
* files and not .txt files. Also, 'Works' here means that the variables
* $foo and $bar are available within the included file. */

// Won't work; file.txt wasn't handled by www.example.com as PHP
include 'http://www.example.com/file.txt?foo=1&bar=2';

// Won't work; looks for a file named 'file.php?foo=1&bar=2' on the
// local filesystem.
include 'file.php?foo=1&bar=2';

// Works.
include 'http://www.example.com/file.php?foo=1&bar=2';

$foo = 1;
$bar = 2;
include 'file.txt'; // Works.
include 'file.php'; // Works.

?>

Warning

Security warning

Remote file may be processed at the remote server (depending on the file extension and the fact if the remote server runs PHP or not) but it still has to produce a valid PHP script because it will be processed at the local server. If the file from the remote server should be processed there and outputted only,readfile() is much better function to use. Otherwise, special care should be taken to secure the remote script to produce a valid and desired code.

Because include() is a special language construct, parentheses are not needed around its argument. Take care when comparing return value.

Example #4 Comparing return value of include

<?php
// won't work, evaluated as include(('vars.php') == 'OK'), i.e. include('')
if (include('vars.php') == 'OK') {
echo 'OK';
}

// works
if ((include 'vars.php') == 'OK') {
echo 'OK';
}
?>

Example #5 include() and the return() statement

return.php
<?php

$var = 'PHP';

return $var;

?>

noreturn.php
<?php

$var = 'PHP';

?>

testreturns.php
<?php

$foo = include 'return.php';

echo $foo; // prints 'PHP'

$bar = include 'noreturn.php';

echo $bar; // prints 1

?>

$bar is the value 1 because the include was successful. Notice the difference between the above examples. The first uses return() within the included file while the other does not. If the file can't be included, FALSE is returned and E_WARNING is issued.

If there are functions defined in the included file, they can be used in the main file independent if they are before return() or after. If the file is included twice, PHP 5 issues fatal error because functions were already declared, while PHP 4 doesn't complain about functions defined after return(). It is recommended to use include once() instead of checking if the file was already included and conditionally return inside the included file.

Another way to "include" a PHP file into a variable is to capture the output by using the Output Control Functions with include(). For example:

Example #6 Using output buffering to include a PHP file into a string

<?php
$string = get_include_contents('somefile.php');

function get_include_contents($filename) {
    if (is_file($filename)) {
        ob_start();
        include $filename;
        $contents = ob_get_contents();
        ob_end_clean();
        return $contents;
    }
    return false;
}

?>