PHP: Checking if a String Starts With Another String (str_starts_with)

• Return value
  Always returns a Boolean value (TRUE if it starts with the substring, FALSE otherwise).
• Case-sensitivity
  Considers uppercase and lowercase differently.
• Functionality
  Checks if a haystack (the main string) starts with a needle (the substring).

Example

$string = "This is a string";
$prefix = "This";

if (str_starts_with($string, $prefix)) {
  echo "The string '$string' starts with the prefix '$prefix'.";
} else {
  echo "The string '$string' does not start with the prefix '$prefix'.";
}

This code will output:

The string 'This is a string' starts with the prefix 'This'.

• For versions prior to PHP 8.0, you can achieve similar functionality using strpos. However, strpos returns the position of the first occurrence of the substring, and you'd need to check if the position is 0 (meaning it starts at the beginning).
• str_starts_with is available in PHP 8.0 and later versions.

$string = "This is a string";
$prefix = "This";

if (strpos($string, $prefix) === 0) {
  echo "The string '$string' starts with the prefix '$prefix'.";
} else {
  echo "The string '$string' does not start with the prefix '$prefix'.";
}

---

Checking for Exact Match (Case-Sensitive)

$url = "https://www.example.com";

if (str_starts_with($url, "http://")) {
  echo "The URL starts with 'http://' (not secure).";
} else if (str_starts_with($url, "https://")) {
  echo "The URL starts with 'https://' (secure).";
} else {
  echo "The URL does not start with a recognized protocol.";
}

Checking Multiple Substrings

$filename = "image1.jpg";

if (str_starts_with($filename, "image") || str_starts_with($filename, "photo")) {
  echo "The filename starts with 'image' or 'photo'.";
} else {
  echo "The filename does not start with 'image' or 'photo'.";
}

Checking with Empty Substring

$text = "Hello world!";

if (str_starts_with($text, "")) { // Empty string check
  echo "The text starts with an empty string (always true).";
} else {
  echo "The text does not start with an empty string (won't reach here)."; // This line won't execute
}

Case-Insensitive Check (using strtolower)

$username = "Username123";

if (str_starts_with(strtolower($username), "admin")) { // Convert both to lowercase
  echo "The username starts with 'admin' (case-insensitive).";
} else {
  echo "The username does not start with 'admin' (case-insensitive).";
}

• For older versions, consider using strpos with additional checks.
• str_starts_with is available in PHP 8.0 and later.

---

Using strpos

The strpos function finds the position of the first occurrence of a substring within a string. You can leverage this to check if the position is 0 (the beginning).

$string = "This is a string";
$prefix = "This";

if (strpos($string, $prefix) === 0) {
  echo "The string '$string' starts with the prefix '$prefix'.";
} else {
  echo "The string '$string' does not start with the prefix '$prefix'.";
}

Using Substring Extraction

This approach extracts a specific length of characters from the beginning of the string and compares it with the desired prefix.

$string = "This is a string";
$prefix = "This";
$extracted = substr($string, 0, strlen($prefix));

if ($extracted === $prefix) {
  echo "The string '$string' starts with the prefix '$prefix'.";
} else {
  echo "The string '$string' does not start with the prefix '$prefix'.";
}

Using Regular Expressions (more complex)

Regular expressions offer powerful pattern matching capabilities. However, they might be less readable for simpler tasks like checking string prefixes.

$string = "This is a string";
$prefix = "This";
$pattern = "^" . $prefix; // "^" matches the beginning of the string

if (preg_match($pattern, $string)) {
  echo "The string '$string' starts with the prefix '$prefix'.";
} else {
  echo "The string '$string' does not start with the prefix '$prefix'.";
}

Choosing the Best Alternative

• If the string manipulation needs involve more complex checks, consider regular expressions.
• For readability and simplicity, strpos is often the preferred choice.

• Explore the substr_compare function in PHP for more granular control over substring comparisons.
• Remember to handle case-sensitivity if needed. You can use strtolower or strtoupper on both the string and the prefix for case-insensitive comparisons.