How to get multiple selected values of select box in php?

html

form-engineering

validation

sanitization

byNikita Barsukov·Jan 11, 2025

To capture multiple selections from a <select multiple> in PHP, you need to name your <select> with square brackets (name="options[]") and loop through the $_POST['options'] array upon form submission.

In your HTML form:

<select name="options[]" multiple>
  <option value="opt1">Option 1</option>
  <option value="opt2">Option 2</option>
  <!-- Even more options here -->
</select>

In your PHP file:

foreach($_POST['options'] as $option) {
  echo htmlspecialchars($option) . ' ';
}

This will echo every selected option, while htmlspecialchars is there to prevent those XSS party crashers.

Choice of method: GET or POST?

In the form-making phase, the method attribute (GET or POST) can be more important than a 5-star spell in a magic battle. Most of the time, POST is recommended for handling multiple selections as it neither exposes data in the URL nor limits data size.

<form action="handler.php" method="post">
  <!-- Here be dragons... I mean, select and other inputs -->
  <input type="submit" value="Submit">
</form>

Security: handling user input

Never trust user input, it's trickier than a leprechaun! Validate and sanitize the input to prevent any nasty surprises. You could use preg_match() for validation and htmlspecialchars() for sanitization - double protection, like a medieval city wall!

foreach($_POST['options'] as $option) {
  // Leprechaun check complete, we're safe to proceed
  if (preg_match("/^[a-zA-Z0-9]+$/", $option)) {
    echo htmlspecialchars($option) . ' '; // The wall stands tall!
  }
}

Seeing into the future: error handling

Let's not pretend that users will always pick an option. Error checking is like your crystal ball:

if (!empty($_POST['options'])) {
  foreach($_POST['options'] as $option) {
    echo htmlspecialchars($option) . ' ';
  }
} else {
  echo 'Please select at least one option.'; // Listen to the crystal ball!
}

PHP classes: all together now!

Imagine having a PHP class dedicated to handling form data, similar to having a mighty lion tamer for your circus of data. It brings methods to validate, sanitize, and process selected options efficiently.

class FormProcessor {
  public function processSelect($options) {
    $processedValues = []; // Empty suitcase, let's pack!
    if (!empty($options)) {
      foreach ($options as $option) {
        $processedValues[] = $option; // Into the suitcase you go!
      }
    }
    return $processedValues; // Voila! Your packed suitcase
  }
}

Make it mandatory: utilizing `required`

Thanks to HTML5, making field selection compulsory is as easy as adding the required attribute to your <select> element. It works hand in hand with your PHP validation.

<select name="options[]" multiple required>
  <option value="opt1">Option 1</option>
  <!-- More options, yeehaw! -->
</select>

Show off with advanced selection handling

For the connoisseurs out there:

JavaScript can dynamize your <select>, like powering a mechanical bull.
For those dealing with a Godzilla-sized dataset, consider techniques like pagination or search functions.
APIs or third-party services: they're your friends, use them.