PHP str_replace Function: How it Works with Examples

If you find a word that does not fit and want to fix it. You can use the PHP str_replace function. This function helps you swap one piece of a string with another.

Understand the str_replace Function in PHP

The str_replace replaces parts of a string with new text. It searches for one value and swaps it with another.

str_replace($search, $replace, $subject, $count)

• $search: The word or value you want to replace.
• $replace: The new word or value.
• $subject: The string or array you want to change.
• $count (optional): PHP stores the number of replacements here.

Here is a quick example:

echo str_replace("world", "PHP", "Hello world");

You get “Hello PHP” because it replaces “world” with “PHP”.

The str_replace checks for exact matches. It does not replace if the case does not match.

echo str_replace("apple", "orange", "Apple pie");

This gives “Apple pie” because “apple” and “Apple” do not match.

Here are the use cases:

• Clean up messy input.
• Format phone numbers.
• Fix file paths.
• Update names in bulk.
• Remove unwanted characters from text.

The Differences Between str_replace, str_ireplace and preg_replace in PHP

Each of these functions replaces text in a string. But they follow different rules.

str_replace:

• Replaces exact text only.
• Case matters.
• No pattern matching.

For example:

str_replace("cat", "dog", "The cat sleeps"); 
str_replace("Cat", "dog", "The cat sleeps");

Output:

The dog sleeps
The cat sleeps

Use it when you want a case-sensitive replacement.

str_ireplace:

• Works like str_replace.
• Ignores case.
• No patterns.
• Slightly slower than str_replace

For example:

str_ireplace("Cat", "dog", "The cat sleeps");

Output:

The dog sleeps

Use it when you do not care about the letter case.

preg_replace:

• Uses patterns (regular expressions).
• Can match flexible formats.
• Slower but powerful.
• Case control with flags.

For example:

preg_replace("/cat/i", "dog", "The CAT sleeps"); 
preg_replace("/[0-9]/", "#", "Room 101");        

The output:

The dog sleeps
Room ###

Use it when you need pattern logic or dynamic matches.

Here is a table that shows you the key differences:

PHP str_replace Examples

Replace multiple values:

echo str_replace(["apple", "banana"], ["orange", "grape"], "apple and banana");

The output:

orange and grape

This swaps “apple” with “orange” and “banana” with “grape”.

str_replace(["a", "e", "i"], "*", "pineapple");

You get “p*n**ppl*”. It replaces each vowel with “*”.

Replace in arrays:

$arr =  str_replace("cat", "dog", ["cat", "wild cat", "black cat"]);
print_r($arr);

Output:

Array
(
    [0] => dog
    [1] => wild dog
    [2] => black dog
)

This changes all “cat” values to “dog” in each array item.

$vlarray= str_replace(["red", "blue"], "color", ["red car", "blue sky"]);
print_r($vlarray);

Output:

Array
(
    [0] => color car
    [1] => color sky
)

It swaps each color with “color”.

Use the $count parameter:

str_replace("apple", "orange", "apple, apple, apple", $count);

Output:

orange, orange, orange

$count becomes 3 because it replaced “apple” three times.

$str = "egg, egg, egg";
str_replace("egg", "bacon", $str, $count);

The string becomes “bacon, bacon, bacon” and $count holds 3.

Replace numbers in the text:

str_replace(["1", "2"], ["one", "two"], "1, 2, 3");

You get “one, two, 3” by replacing numbers with words.

Clean up extra spaces:

str_replace("  ", " ", "This  is  a  test");

You get “This is a test” by removing extra spaces.

Wrapping Up

In this article, you learned what str_replace does and how it works with strings and arrays. You saw its syntax, how it checks for case, and how to use the $count variable. Here is a quick recap:

• str_replace replaces text in strings or arrays.
• It works with exact values.
• You can replace one value or many at once.
• Use $count to know how many changes happened.
• Pick str_replace, str_ireplace, or preg_replace based on your case.

FAQs