PHP: Check if a string contains a substring

Introduction

In PHP, working with text often involves determining if a specific sequence of characters, or substring, exists within another string. This process is essential for tasks like validating input, searching content, and processing text data.

Checking for the presence of substrings within strings is a common operation in web development. In PHP, several functions can help you reliably check whether a substring exists within a larger string. This article walks through various PHP functions, from the most straightforward methods to more complex approaches, for performing this check.

Using strpos() and stripos()

The strpos() function is one of the simplest ways to check for the presence of a substring. It finds the position of the first occurrence of a substring in a string. The function is case-sensitive, which means that searching for ‘apple’ is different from ‘Apple’. If you need a case-insensitive search, use stripos() instead.

if (strpos('Hello world', 'world') !== false) {
    echo 'The substring exists.';
} else {
    echo 'The substring does not exist.';
}

if (stripos('Hello world', 'World') !== false) {
    echo 'The substring exists, case-insentively.';
} else {
    echo 'The substring does not exist.';
}

Using strstr() and stristr()

Another way to detect a substring is using strstr() and stristr(). These functions return the part of the string starting from and including the first occurrence of the substring. If the substring is not found, they return false.

$content = 'This is a simple text';
$substring = 'simple';

if (strstr($content, $substring)) {
    echo 'The substring "' . $substring . '" exists.';
} else {
    echo 'The substring does not exist.';
}

// Case-insensitive search
if (stristr($content, $substring)) {
    echo 'The substring "' . $substring . '" exists, case-insensitively.';
} else {
    echo 'The substring does not exist.';
}

Using preg_match()

For more complex pattern matching, preg_match() utilizing regular expressions can be employed. This is particularly useful if the substring follows a specific format or pattern.

$text = 'Contact us at [email protected]';
$pattern = '/info\@[a-z]+\.com/';

if (preg_match($pattern, $text)) {
    echo 'The pattern is detected in the string.';
} else {
    echo 'Pattern not detected.';
}

Using substr_count()

If you wish to count how many times a substring appears in a string, substr_count() is the function to use. It provides the number of occurrences of the substring.

$str = 'This is the way. The way is hard but fair.';
$needle = 'way';

$count = substr_count($str, $needle);
echo 'The substring appears ' . $count . ' times.';

Working with Multibyte Strings

PHP also provides functions to handle multibyte strings, such as those containing characters from languages other than English. Functions like mb_strpos() and mb_stripos() allow for proper detection of substrings in multibyte scenarios.

$text = '这是一些中文';
$substring = '中文';

if (mb_strpos($text, $substring) !== false) {
    echo 'The multibyte substring exists.';
} else {
    echo 'The multibyte substring does not exist.';
}

Conclusion

In conclusion, PHP offers developers a variety of functions for checking the presence of substrings, providing the flexibility to select an approach that best suits the task. Whether you need a case-sensitive or insensitive search, count occurrences, or deal with multibyte strings, PHP has the tools necessary to perform these checks effectively.