WebCodeDoc

PHP str_replace() Function

Quick summary: The PHP str_replace() function replaces all occurrences of a search string with a replacement string.

PHP str_replace() Syntax 

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

PHP str_replace() Basic examples 

$text = "Hello world";
echo str_replace("world", "PHP", $text);
PHP
Output:
Hello PHP

Replaces a substring with another string.

$text = "foo bar foo";
echo str_replace("foo", "baz", $text);
PHP
Output:
baz bar baz

Replaces all occurrences, not just the first.

$text = "abc";
echo str_replace("x", "y", $text);
PHP
Output:
abc

If the search string is not found, the original string is returned.

PHP str_replace() Real-world usage 

$filename = "report final.pdf";
echo str_replace(" ", "_", $filename);
PHP
Output:
report_final.pdf

Normalizes filenames by replacing spaces.

$input = "<script>alert(1)</script>";
echo str_replace(["<", ">"], ["&lt;", "&gt;"], $input);
PHP
Output:
&lt;script&gt;alert(1)&lt;/script&gt;

Performs basic escaping by replacing multiple values.

PHP str_replace() Edge cases 

$text = "aaaa";
echo str_replace("aa", "b", $text);
PHP
Output:
bb

Replacements do not overlap.

$text = "test";
echo str_replace("", "x", $text);
PHP
Output:
test

An empty search string results in no changes.

PHP str_replace() Common mistakes

Expecting case-insensitive replacement

str_replace() is case-sensitive.

Incorrect
echo str_replace("hello", "Hi", "Hello");
Correct
echo str_ireplace("hello", "Hi", "Hello");

Use str_ireplace() for case-insensitive replacements.

PHP str_replace() Frequently Asked Questions

What does str_replace() do in PHP?

str_replace() replaces all occurrences of a search string with a replacement string.

Is str_replace() case-sensitive?

Yes, str_replace() is case-sensitive. Use str_ireplace() for case-insensitive replacement.

Can str_replace() replace multiple values at once?

Yes, you can pass arrays for search and replace parameters to replace multiple values in one call.

Does str_replace() modify the original string?

No, str_replace() returns a new string and does not modify the original variable unless reassigned.

What happens if the search value is not found?

str_replace() returns the original string unchanged if no matches are found.

Can str_replace() work with arrays?

Yes, str_replace() can operate on arrays of strings and return an array of results.

What is the difference between str_replace() and preg_replace()?

str_replace() performs simple string replacement, while preg_replace() uses regular expressions.

Does str_replace() replace overlapping matches?

No, str_replace() replaces non-overlapping occurrences from left to right.

Can str_replace() count replacements?

Yes, you can pass a fourth parameter to store the number of replacements made.

Is str_replace() fast?

Yes, str_replace() is a fast built-in function suitable for most string replacement tasks.

What is a real-world use case of str_replace()?

str_replace() is commonly used to sanitize input, replace placeholders, or clean strings.

How to remove a substring using str_replace()?

Replace the substring with an empty string, for example str_replace("text", "", $string).

PHP str_replace() Related PHP Functions