PHP substr() Function

What does substr() do?

substr() extracts a portion of a string starting at $offset. A negative offset counts from the end of the string, and a negative length stops that many bytes before the end.

Syntax

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

Parameters

• $string - The input string.
• $offset - Start position (0-based). Negative values count from the end: -1 is the last byte.
• $length - Optional number of bytes to return. Omitted or null means "to the end". A negative value leaves that many bytes off the end.

Return value

The extracted substring. Since PHP 8.0 it returns an empty string (instead of false) when $offset is past the end of the string.

substr() examples

Every example below shows the exact output it produces. Paste any of them into the editor above (or the online compiler) to run it.

1. Positive and negative offsets

<?php
$text = "Hello, World!";
echo substr($text, 0, 5) . "\n";   // first 5 characters
echo substr($text, 7) . "\n";      // from position 7 to the end
echo substr($text, -6) . "\n";     // last 6 characters
echo substr($text, -6, 5) . "\n";  // 5 characters, starting 6 from the end
echo substr($text, 0, -1) . "\n";  // everything except the last character

Output:

Hello
World!
World!
World
Hello, World

2. Truncate text with an ellipsis

<?php
function excerpt(string $text, int $max): string {
    if (strlen($text) <= $max) {
        return $text;
    }
    return rtrim(substr($text, 0, $max)) . "...";
}
echo excerpt("PHP is a popular general-purpose scripting language.", 20) . "\n";
echo excerpt("Short text", 20) . "\n";

Output:

PHP is a popular gen...
Short text

3. Get a file extension and handle out-of-range offsets

<?php
$file = "report.final.pdf";
echo substr($file, strrpos($file, ".") + 1) . "\n";
var_dump(substr("abc", 5));

Output:

pdf
string(0) ""

Common mistakes and gotchas

• Byte-based: substr() can cut a UTF-8 character in half. Use mb_substr() for multibyte text.
• PHP 7 vs PHP 8: code that checks substr(...) === false no longer works in PHP 8, where an out-of-range offset returns "".
• File extensions: pathinfo($file, PATHINFO_EXTENSION) is more robust than substr() + strrpos() for paths without a dot.