Check if a substring occurs within a string in PHP

This article demonstrates how to check if a substring occurs within a string in PHP.

1. Using `strpos()` function

The strpos() function returns the index of the first occurrence of a substring in a string, and false if the substring is not found. To check if a substring is found in a string or not, you can test the return value of strpos() using the !== operator.

The following example demonstrates its usage. Take note of the !== operator. You cannot use the equality operator (!=) or the negation operator (!) here. The strpos() function returns 0 if the substring is found at the beginning of the string, and both 0 != false and !0 evaluate to false, and 0 !== false evaluates to true.

<?php

$text = "Some string";

$substr = 'str';

if (strpos($text, $substr) !== false) {

echo 'Substring found';

}

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You may want to create a utility function that accepts two arguments, $haystack and $needle, and returns true if $needle is a substring of $haystack; false otherwise.

<?php

function contains($haystack, $needle)

{

return strpos($haystack, $needle) !== false;

}

$text = "Some string";

$substr = 'str';

if (contains($text, $substr)) {

echo 'Substring found';

}

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To make the search case-insensitive, use the stripos() method. It is similar to strpos(), but is case-insensitive.

<?php

// Returns `true` if `$needle` is a substring of `$haystack` with case ignored;

// `false` otherwise

function containsCaseIgnored($haystack, $needle)

{

return stripos($haystack, $needle) !== false;

}

$text = "Some string";

$substr = 'String';

if (containsCaseIgnored($text, $substr)) {

echo 'Substring found';

}

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2. Using `strstr()` function

Another option is to use the strstr() function to determine if a particular substring occurs within a string. It returns the portion of the string starting from the substring’s first occurrence till its end, or false if the substring is not found.

<?php

$text = "Some string";

$substr = 'str';

if (strstr($text, $substr)) {

echo 'Substring found';

}

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Note that strpos() is faster and less memory-intensive than the strstr() function. Also note that the search performed by the strstr() function is case-sensitive. For a case-insensitive search, you can use the stristr() method.

<?php

$text = "Some string";

$substr = 'String';

if (stristr($text, $substr)) {

echo 'Substring found';

}

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3. Using `preg_match()` function

Finally, you can use the preg_match() function to perform a regular expression match that checks if a substring occurs within a string. It returns 1 in the case of a match, and 0 in the case of no match.

The following code demonstrates its usage. On failure, the preg_match() function can return false (or a value that evaluates to false). Therefore, you should always use the === operator for checking the return value of this function.

<?php

$text = "Some string";

$substr = 'str';

if (preg_match("/{$substr}/", $text) === 1) {

echo 'Substring found';

}

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Note that preg_match() is overkill for such a trivial task. It uses regular expressions, which causes it to perform slower than the strpos() and strstr() functions. For a case-insensitive search, you can place i at the end of a regular expression.

<?php

// Returns `true` if `$needle` is a substring of `$haystack` ignoring case;

// `false` otherwise

function containsCaseIgnored($haystack, $needle)

{

return preg_match("/{$needle}/i", $haystack) === 1;

}

$text = "Some string";

$substr = 'String';

if (containsCaseIgnored($text, $substr)) {

echo 'Substring found';

}

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4. Using `substr_count()` function

As a bonus, here’s another approach to checking if a substring occurs within a string. It uses the substr_count() function, which counts the number of times the substring occurs in the string. If that count is greater than 0, then we can say that the substring occurs within a string.

<?php

$text = "Some string";

$substr = 'str';

if (substr_count($text, $substr) > 0) {

echo 'Substring found';

}

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Note that the search is case-sensitive. To make the search case-insensitive, you can convert the string and the substring to the same case (both uppercase or both lowercase).

<?php

$text = "Some string";

$substr = 'String';

if (substr_count(strtolower($text), strtolower($substr)) > 0) {

echo 'Substring found';

}

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That’s all about determining if a substring occurs within a string in PHP.

Check if a substring occurs within a string in PHP

1. Using strpos() function

2. Using strstr() function

3. Using preg_match() function

4. Using substr_count() function

Share this:

1. Using `strpos()` function

2. Using `strstr()` function

3. Using `preg_match()` function

4. Using `substr_count()` function