How To Use StartsWith() And EndsWith() Functions In PHP?

Using str_starts_with() Function

The str_starts_with() function checks if a string starts with a given substring. Its syntax is:

str_starts_with(string $haystack, string $needle): bool

Here's an example:

$str = '|apples}';
$result = str_starts_with($str, '|');
var_dump($result); // Output: bool(true)

$str = 'Apple pie';
$result = str_starts_with(strtolower($str), 'apple');
var_dump($result); // Output: bool(true)

Using str_ends_with() Function

The str_ends_with() function checks if a string ends with a given substring. Its syntax is:

str_ends_with(string $haystack, string $needle): bool

Here's an example:

$str = '|apples}';
$result = str_ends_with($str, '}');
var_dump($result); // Output: bool(true)

Both functions return a boolean value: true if the string starts or ends with the specified substring, and false otherwise. These built-in functions offer a simple way to perform prefix and suffix checks in PHP 8.0 and later versions.

Implementing startsWith() Function

The startsWith() function checks if a string begins with a specific substring. Here's how to implement it:

function startsWith($haystack, $needle) {
    $length = strlen($needle);
    return substr($haystack, 0, $length) === $needle;
}

Function logic:

1. Get the length of the needle (substring to check for).
2. Extract a substring from the haystack (main string) with the same length as the needle, starting from the beginning.
3. Compare the extracted substring with the needle.

Parameters and return value:

• $haystack: The main string to check.
• $needle: The substring to look for at the start of the haystack.
• Returns: true if the haystack starts with the needle, false otherwise.

$text = "Hello, World!";
$prefix = "Hello";

if (startsWith($text, $prefix)) {
    echo "The string starts with 'Hello'";
} else {
    echo "The string does not start with 'Hello'";
}

Implementing endsWith() Function

The endsWith() function checks if a string ends with a specific substring. Here's the implementation:

function endsWith($haystack, $needle) {
    $length = strlen($needle);
    if ($length == 0) {
        return true;
    }
    return substr($haystack, -$length) === $needle;
}

Function logic:

1. Get the length of the needle.
2. If the needle is empty, return true (an empty string is considered to end any string).
3. Extract a substring from the haystack with the same length as the needle, starting from the end.
4. Compare the extracted substring with the needle.

Parameters and return value:

• $haystack: The main string to check.
• $needle: The substring to look for at the end of the haystack.
• Returns: true if the haystack ends with the needle, false otherwise.

function startsWithInsensitive($haystack, $needle) {
    $length = strlen($needle);
    return strtolower(substr($haystack, 0, $length)) === strtolower($needle);
}

function endsWithInsensitive($haystack, $needle) {
    $length = strlen($needle);
    if ($length == 0) {
        return true;
    }
    return strtolower(substr($haystack, -$length)) === strtolower($needle);
}

These custom functions provide a way to check string prefixes and suffixes in PHP versions before 8.0, mimicking the functionality of the built-in functions introduced later.

Validating File Extensions

The endsWith() function helps check file extensions. You can use it to validate uploaded files or filter files by type. Here's an example of using endsWith() for file type checking:

function isImageFile($filename) {
    $allowedExtensions = ['.jpg', '.jpeg', '.png', '.gif'];
    foreach ($allowedExtensions as $extension) {
        if (endsWith(strtolower($filename), $extension)) {
            return true;
        }
    }
    return false;
}

// Usage
$file1 = "image.jpg";
$file2 = "document.pdf";

echo isImageFile($file1) ? "File 1 is an image" : "File 1 is not an image";
echo "\n";
echo isImageFile($file2) ? "File 2 is an image" : "File 2 is not an image";

This function checks if a filename ends with an allowed image extension. It uses strtolower() to make the check case-insensitive.

URL Protocol Verification

The startsWith() function helps check URL protocols. You can use it to validate or group URLs by their protocols. Here's an example:

function getUrlProtocol($url) {
    $protocols = ['http://', 'https://', 'ftp://'];
    foreach ($protocols as $protocol) {
        if (startsWith(strtolower($url), $protocol)) {
            return $protocol;
        }
    }
    return 'Unknown';
}

// Usage
$url1 = "https://www.example.com";
$url2 = "ftp://ftp.example.com";
$url3 = "www.example.com";

echo "URL 1 protocol: " . getUrlProtocol($url1) . "\n";
echo "URL 2 protocol: " . getUrlProtocol($url2) . "\n";
echo "URL 3 protocol: " . getUrlProtocol($url3);

This function checks if a URL starts with a common protocol. It returns the matched protocol or 'Unknown' if no match is found. The strtolower() function makes the check case-insensitive.

These examples show how you can use startsWith() and endsWith() functions in PHP for common string comparison tasks.

function isCompanyEmail($email) {
    $allowedDomains = ['@company.com', '@company.org'];
    foreach ($allowedDomains as $domain) {
        if (endsWith(strtolower($email), $domain)) {
            return true;
        }
    }
    return false;
}

// Usage
$email1 = "user@company.com";
$email2 = "user@gmail.com";

echo isCompanyEmail($email1) ? "Email 1 is a company email" : "Email 1 is not a company email";
echo "\n";
echo isCompanyEmail($email2) ? "Email 2 is a company email" : "Email 2 is not a company email";