PHP: Check If a String Contains a Substring

Checking for a substring in a string is one of the most common tasks a developer does. In PHP, there’s more than one way to accomplish this task. Today, we will learn all the different ways to check if a string contains a substring in PHP.

Case Sensitive Matching

Below we will look at different ways to search for a substring that matches the exact casing in the given string.

Using Strpos()

You can use strpos() to find the first occurrence of a substring in a string. This method is one of the most common methods used for finding a substring.

Usage

strpos ( string $haystack , mixed $needle [, int $offset = 0 ] ) : int

strpos() accepts the following parameters:

• $haystack: the string that you will search in
• $needle: the substring that you’re searching for
• $offset (optional): defines the character index to begin from. If you pass a negative number, then it begins from the end of the string.

Example:

    /**
     * A method to find substring in a string
     * 
     * @param String $stringToSearch This is the sub string you want to search
     * @param String $searchString   The is the string in which substring
     *                               will be searched for
     *                                
     * @return boolean                true if $stringToSearch exists
     *                                in $searchString, false otherwise
     */
    public function findString($stringToSearch, $searchString) {
        if (strpos($stringToSearch, $searchString) !== false) {
            return true;
        } else {
            return false;
        }
    }

In the above example, we made a custom method that uses strpos() to search for a given substring in a string and returns a boolean value that determines whether a match was found. The method can be used like this:

echo  $this->findString('code on codezen.io', 'code'); // output => true
echo  $this->findString('code on codezen.io', 'sing'); // output => false

Using $offset

Here is an example of how you could use $offset to exclude a certain number of characters from start or end in your search. In the following example, the search begins from the second character (or character index of 1):

<?php
// Here search for the character and ignore anything before the offset
$newstring = 'code on codezen.io';
$pos = strpos($newstring, 'code', 1); // $pos = 9, not 0
?>

Regex based matching using preg_match()

We can also use regular expressions to find a substring in a string. To do this, we make use of PHP’s preg_match() method to perform a regular expression match against a string.

preg_match ( string $pattern , string $subject [, array &$matches [, int $flags = 0 [, int $offset = 0 ]]] ) : int

preg_match() searches the given $subject for a match to the regular expression given in $pattern.

    /**
     * A method to find substring in a string using preg_match
     *
     * @param String $pattern        This is the sub string you want to search
     * @param String $searchString   The is the string in which substring
     *                               will be searched for
     *
     * @return boolean                true if $stringToSearch exists
     */
    public function findStringPattern($pattern, $searchString) {

        if (preg_match('/\b'.$pattern.'\b/', $searchString)) {
            return true;
        } else {
            return false;
        }
    }

The above method can be used like this:

echo  $this->findStringPattern('code on codezen.io', 'code'); // output => true
echo  $this->findStringPattern('code on codezen.io', 'sing'); // output => false

Case-Insensitive Matching

In the previous section, you learned how to do a case-sensitive search for a substring. In this section, we’ll learn how to do a case-insensitive search.

Use stripos() for case-insensitive matching

If you want to match a substring regardless of its case, you can use PHP’s stripos() method. This function works similarly to the strpos() method that we discussed initially.

stripos() accepts the following parameters:

• $haystack: the string that you will search in
• $needle: the substring that you’re searching for
• $offset (optional): defines the character index to begin from. If you pass a negative number, then it begins from the end of the string.

stripos ( string $haystack , mixed $needle [, int $offset = 0 ] ) : int

Here is an example of how you can use stripos() in your application:

    /**
     * A method to find case insensitive substring in a string
     *
     * @param String $stringToSearch This is the sub string you want to search
     * @param String $searchString   The is the string in which substring
     *                               will be searched for
     *
     * @return boolean                true if $stringToSearch exists
     *                                in $searchString, false otherwise
     */
    public function findCaseInsensitiveString($stringToSearch, $searchString) {
        if (stripos($stringToSearch, $searchString) !== false) {
            return true;
        } else {
            return false;
        }
    }

In the above example, we made a custom made that uses stripos() to search for a given substring in a string and returns a boolean value that determines whether a match was found. The method can be used like this:

echo  $this->findCaseInsensitiveString('code on codezen.io', 'code'); // output => true
echo  $this->findCaseInsensitiveString('code on codezen.io', 'Code'); // output => false

Find Number of Occurrences of a Substring

If you want to find out the number of times a substring appears in a given string, you can use the substr_count() method.

substr_count ( string $haystack , string $needle [, int $offset = 0 [, int $length ]] ) : int

Similar to the methods discussed above you need to pass a string ($haystack) and a substring ($needle) to search. We will see an example usage below:

$searchString = "learn how to code with codezen.io";
$stringToSearch = "code";
$count = substr_count($searchString, $stringToSearch);
echo "The count is: " . $count;

Output

The count is: 2

Wrapping Up

These are some of the different ways to search for a particular word, phrase, or string within another string. If you have any questions or requests, feel free to drop a comment below.

Also, be sure to check out our PHP tutorials for interesting articles like this one.