String Prefix and Suffix Checks in PHP

Checking String Beginnings and Endings in PHP

Often when working with strings in PHP, you’ll need to determine if a string starts with or ends with a specific substring. This is a common task in data validation, parsing, and text manipulation. This tutorial will cover various techniques to accomplish this, ranging from PHP 8.0’s built-in functions to compatible solutions for older versions.

PHP 8.0 and Later: str_starts_with() and str_ends_with()

PHP 8.0 introduced dedicated functions for checking string prefixes and suffixes, making the code cleaner and more readable.

• str_starts_with(string $haystack, string $needle): bool: Returns true if the haystack string starts with the needle substring, and false otherwise.
• str_ends_with(string $haystack, string $needle): bool: Returns true if the haystack string ends with the needle substring, and false otherwise.

These functions are case-sensitive.

<?php

$string = '|apples}';

if (str_starts_with($string, '|')) {
    echo "Starts with '|'\n"; // Output: Starts with '|'
}

if (str_ends_with($string, '}')) {
    echo "Ends with '}'\n"; // Output: Ends with '}'
}

?>

These functions are generally the most efficient and preferred method when working with PHP 8.0 or later.

Compatibility with Older PHP Versions

If you need to support PHP versions older than 8.0, you’ll need to implement these checks manually. Here are a few common approaches:

1. Using substr() and Comparison

This method extracts a substring from the beginning or end of the haystack and compares it to the needle.

<?php

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

function endsWith(string $haystack, string $needle): bool {
    $length = strlen($needle);
    if (!$length) { //Handle empty needle
        return true;
    }
    return substr($haystack, -$length) === $needle;
}

$string = '|apples}';

if (startsWith($string, '|')) {
    echo "Starts with '|'\n";
}

if (endsWith($string, '}')) {
    echo "Ends with '}'\n";
}

?>

2. Using substr_compare()

The substr_compare() function is designed for string comparisons and can be used to check for prefixes and suffixes.

<?php

function startsWith(string $haystack, string $needle): bool {
    return substr_compare($haystack, $needle, 0, strlen($needle)) === 0;
}

function endsWith(string $haystack, string $needle): bool {
    return substr_compare($haystack, $needle, -strlen($needle)) === 0;
}

$string = '|apples}';

if (startsWith($string, '|')) {
    echo "Starts with '|'\n";
}

if (endsWith($string, '}')) {
    echo "Ends with '}'\n";
}

?>

3. Using strpos() and strrpos()

These functions find the position of a substring within a string. We can leverage them to check for prefixes and suffixes.

<?php

function startsWith(string $haystack, string $needle): bool {
    return strpos($haystack, $needle, 0) === 0;
}

function endsWith(string $haystack, string $needle): bool {
    $expectedPosition = strlen($haystack) - strlen($needle);
    return strrpos($haystack, $needle, 0) === $expectedPosition;
}

$string = '|apples}';

if (startsWith($string, '|')) {
    echo "Starts with '|'\n";
}

if (endsWith($string, '}')) {
    echo "Ends with '}'\n";
}

?>

Performance Considerations

While all these methods are functional, performance can vary. Generally:

• str_starts_with() and str_ends_with() (PHP 8.0+) are the most efficient due to their optimized implementation.
• substr_compare() is often faster than substr() based solutions.
• strpos() and strrpos() can be efficient but might involve more overhead than dedicated prefix/suffix checks.

If performance is critical, it’s recommended to benchmark different approaches with your specific use case to determine the most efficient solution. However, for most typical applications, the difference will likely be negligible.

Case-Insensitive Checks

If you need to perform case-insensitive checks, you can use the strcasecmp() function within a similar startsWith() or endsWith() implementation, or use stripos() and strripos() instead of their case-sensitive counterparts. For example:

<?php

function startsWithCaseInsensitive(string $haystack, string $needle): bool {
    return strcasecmp(substr($haystack, 0, strlen($needle)), $needle) === 0;
}
?>