How to Replace Text in a String in PHP Easily

In PHP, you can replace text in a string using the str_replace function. It takes the text to find, the replacement text, and the original string, then returns a new string with replacements done.

Syntax

The str_replace function replaces all occurrences of a search string with a replacement string in the given original string.

• search: The text you want to replace.
• replace: The text you want to use instead.
• subject: The original string where replacements happen.
• The function returns a new string with replacements applied.

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 simple string.

php

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

Output

Hello PHP!

Common Pitfalls

One common mistake is expecting str_replace to change the original string directly. It does not modify the original string but returns a new one. Also, be careful when replacing overlapping or similar substrings, as replacements happen in one pass.

php

<?php
// Wrong: expecting original string to change
$original = "apple";
str_replace("a", "b", $original);
echo $original; // still "apple"

// Right: assign the result
$original = "apple";
$modified = str_replace("a", "b", $original);
echo $modified; // "bpple"
?>

Output

apple
bpple

Quick Reference

Function	Purpose	Example Usage
str_replace	Replace all occurrences of a string	str_replace('cat', 'dog', 'cat and cat')
str_ireplace	Case-insensitive replace	str_ireplace('Cat', 'dog', 'Cat and cat')
preg_replace	Replace using regular expressions	preg_replace('/cat/i', 'dog', 'Cat and cat')

Key Takeaways

Use str_replace to replace text in strings and assign the result to a variable.

str_replace does not change the original string but returns a new one.

For case-insensitive replacement, use str_ireplace.

For complex patterns, use preg_replace with regular expressions.

Always test your replacements to avoid unexpected results with similar substrings.