How to Use substr in PHP: Syntax and Examples

In PHP, use the substr function to get a part of a string by specifying the string, the start position, and optionally the length. For example, substr('Hello', 1, 3) returns ell.

Syntax

The substr function extracts a substring from a string.

• string: The original string you want to cut from.
• start: The position to start (0-based index). If negative, counts from the end.
• length (optional): How many characters to take. If omitted, takes till the end.

php

substr(string $string, int $start, ?int $length = null): string

Example

This example shows how to extract parts of a string using substr. It extracts 'ell' from 'Hello' and 'world' from 'Hello world'.

php

<?php
$text = 'Hello world';
$part1 = substr($text, 1, 3); // starts at index 1, length 3
$part2 = substr($text, 6);    // starts at index 6, till end

echo $part1 . "\n";
echo $part2 . "\n";
?>

Output

ell
world

Common Pitfalls

Common mistakes include:

• Using a start index larger than the string length returns an empty string.
• Negative length values are not allowed and cause unexpected results.
• Not handling multibyte (Unicode) strings properly; substr works byte-wise, so use mb_substr for UTF-8 strings.

php

<?php
// Wrong: start index too large
echo substr('Hi', 5); // outputs empty string

// Correct: check length before calling
$start = 5;
$text = 'Hi';
if ($start < strlen($text)) {
    echo substr($text, $start);
} else {
    echo 'Start index too large';
}
?>

Output

Start index too large

Quick Reference

Parameter	Description	Example
string	The original string	'Hello world'
start	Start position (0-based). Negative counts from end	1 or -5
length	Number of characters to extract (optional)	3 or omitted

Key Takeaways

Use substr(string, start, length) to extract parts of a string in PHP.

Start index is zero-based; negative start counts from the string end.

Omitting length extracts till the string's end.

substr works byte-wise; use mb_substr for multibyte strings.

Check start and length values to avoid empty or unexpected results.