How to Check if String Contains Substring in PHP

In PHP, you can check if a string contains a substring using the strpos() function. It returns the position of the substring or false if not found, so check with strict comparison !== false to confirm presence.

Syntax

The strpos() function searches for the first occurrence of a substring inside a string.

• haystack: The main string to search in.
• needle: The substring to find.
• Returns the position (0-based index) if found, or false if not found.

Use strict comparison !== false to check if substring exists because position 0 is valid.

php

int|false strpos(string $haystack, string $needle)

Example

This example shows how to check if the word "world" is inside the string "Hello world!" and prints a message accordingly.

php

<?php
$text = "Hello world!";
$search = "world";

if (strpos($text, $search) !== false) {
    echo "Found '$search' in the text.";
} else {
    echo "Did not find '$search' in the text.";
}

Output

Found 'world' in the text.

Common Pitfalls

A common mistake is to check if (strpos(...) == false) which fails when the substring is at position 0 (start of string). Always use strict comparison !== false.

php

<?php
// Wrong way
$text = "hello";
if (strpos($text, "he") == false) {
    echo "Not found (wrong check).";
} else {
    echo "Found (wrong check).";
}

// Right way
if (strpos($text, "he") !== false) {
    echo "Found (correct check).";
} else {
    echo "Not found (correct check).";
}

Output

Not found (wrong check).Found (correct check).

Quick Reference

Remember these tips when checking substrings in PHP:

• Use strpos() to find substring position.
• Check with !== false to confirm substring exists.
• Substring at start returns 0, which is false in loose comparison.
• Use stripos() for case-insensitive search.

Key Takeaways

Use strpos() to check if a substring exists in a string in PHP.

Always compare strpos() result with !== false to avoid errors when substring is at position 0.

strpos() returns the position of the substring or false if not found.

Use stripos() for case-insensitive substring checks.

Avoid loose comparison (== false) when checking strpos() results.