How to Use str_replace in PHP: Simple String Replacement

Use str_replace($search, $replace, $subject) in PHP to replace all occurrences of $search with $replace in the string $subject. It returns the modified string without changing the original.

Syntax

The str_replace function has three main parts:

• $search: The text you want to find.
• $replace: The text you want to use instead.
• $subject: The string where the replacement happens.

It returns a new string with replacements done.

php

str_replace(string|array $search, string|array $replace, string|array $subject, int &$count = null): string|array

Example

This example shows how to replace the word "world" with "PHP" in a sentence.

php

<?php
$text = "Hello world!";
$newText = str_replace("world", "PHP", $text);
echo $newText;
?>

Output

Hello PHP!

Common Pitfalls

One common mistake is expecting str_replace to change the original string. It returns a new string instead, so you must save or use the returned value.

Also, if you use arrays for $search and $replace, make sure they match in size to avoid unexpected results.

php

<?php
// Wrong: original string unchanged
$text = "apple";
str_replace("a", "b", $text);
echo $text; // outputs 'apple'

// Right: save the result
$text = "apple";
$text = str_replace("a", "b", $text);
echo $text; // outputs 'bpple'
?>

Output

apple
bpple

Quick Reference

Parameter	Description
$search	Text or array of texts to find
$replace	Text or array of texts to replace with
$subject	String or array of strings to search in
$count (optional)	Variable to store number of replacements made

Key Takeaways

str_replace returns a new string with replacements; original string stays unchanged.

Use matching array sizes for $search and $replace to avoid unexpected results.

Always save or use the returned value from str_replace.

You can replace multiple different texts at once by passing arrays.

str_replace is case-sensitive; use str_ireplace for case-insensitive replacements.