The task of require() and require_once() are the same, but the one difference is that the require() function does not check the file has been included before or not but the require_once() function check the file has been included before or not. If the file has been included in the script before, then the require_once() function will not include the same file again. How the require_once() function is used to include files in PHP has been shown in this tutorial.
Syntax
or
This function has one argument that contains the path of the file that will be included. If the path does not exist, then this function will generate an error. If the path exists and the file has not been included before in the script then it will include the file and returns true, otherwise, it will just return true.
Different Uses of require_once() Function
Create a PHP file named arithmetic.php with the following script to check the use of the require_once() function. Four functions have been declared in the script to perform addition, subtraction, multiplication, and division operations. This file has been used in the examples shown in this part of the tutorial.
//Add function
function Addition($a, $b)
{
return $a + $b;
}
//Subtract function
function Subtraction($a, $b)
{
return $a - $b;
}
//Multiply function
function Multiplication($a, $b)
{
return $a * $b;
}
//Division function
function Division($a, $b)
{
return $a / $b;
}
?>
Example-1: Use of require_once() to Include an Existing File
Create a PHP file with the following script to show the way of including a file in the script. The arithmetic.php file that is created before has been included at the beginning of the script. Two integer variables have been declared and called the Addition() and Multiplication() functions that have been defined in the arithmetic.php file to add and multiply the values of the variables.
//Include the file
require_once('arithmetic.php');
//Assign two numeric values
$number1 = 50;
$number2 = 40;
//Call the Addition() function
echo "The sum of $number1 and $number2 is ".Addition($number1, $number2);
//Call the Multiplication() function
echo "<br/>The multiplication of $number1 and $number2 is ".Multiplication($number1, $number2);
?>
Output:
The following output will appear after executing the above script. The output shows the addition and the multiplication results.
Example-2: Use of Require_once() to Include an Existing File Multiple Times
Create a PHP file with the following script to check how the script works if the require_once() function is used multiple times to include the same file. The arithmetic.php file has been included two times in the script. Next, the Addition() and Multiplication() functions have been called to do the same task that has been shown in the previous example.
//Include the file
require_once('arithmetic.php');
//Assign two numeric values
$number1 = 50;
$number2 = 40;
//Include the file again
require_once('arithmetic.php');
//Call the Addition() function
echo "The sum of $number1 and $number2 is ".Addition($number1, $number2);
//Call the Multiplication() function
echo "<br/>The multiplication of $number1 and $number2 is ".Multiplication($number1, $number2);
?>
Output:
The following output will appear after executing the above script. The output shows the addition and the multiplication results without any error.
Example-3: Use of require_once() to Include a File that Does Not Exist
Create a PHP file with the following script to check how the require_once () function works if the file that is used in the function does not exist. Here, the concat.php file has been used in the require_once() function that does not exist.
//Include the file that does not exist
require_once('concat.php');
//Assign two string values
$string1 = "Hello";
$string2 = "World";
echo "$string1 $string2";
?>
Output:
The following output will appear after executing the above script. The output shows a warning message and a fatal error for the non-existing file.
Example-4: Use of require_once() After Checking the Existence of the File
The error shown in the previous example can be removed by checking the existence of the file before including the file. Create a PHP file with the following script that will check the existence of the file before using the require_once() function. The built-in PHP function, file_exists() has been used in the script to check the existence of the arithmetic.php file.
If this function returns true the arithmetic.php file will be included in the script by using the require_once() function and the Addition() function will be called to calculate the sum of two float numbers.
The file_exists() function has been used for the concat.php file also before including. If the file exists then two string values will be concatenated by using the combine_str() function. An error message will be displayed if the file_exists() function will return false.
$filename = 'arithmetic.php';
if(file_exists($filename))
{
//Include the file
require_once($filename);
//Assign two numeric values
$number1 = 5.67;
$number2 = 4.23;
//Call the Addition() function
echo "The sum of $number1 and $number2 is ".Addition($number1, $number2);
}
else
echo "The $filename does not exist.";
$filename = 'concat.php';
if(file_exists($filename))
{
//Include the file
require_once($filename);
//Assign two string values
$string1 = "Linux";
$string2 = "Hint";
//Call the combine_str() function
echo "The concatenation value is ".combine_str($string1, $string2);
}
else
echo "<br/>The $filename does not exist.";
?>
Output:
The following output will appear after executing the above script. The output shows that the arithmetic.php file exists and the concate.php file does not exist.
Conclusion
The require_once() is a very useful function to include any script inside another PHP script instead of writing the same script in multiple files. The way to use this function has shown in this tutorial by using various examples to help the new PHP user.
