PHP 8 reference · String Functions

PHP substr() Function

Return part of a string, given a start position and an optional length. Negative values count from the end.

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Syntax

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

Parameter	Description
`string`	The input string.
`offset`	Start position from 0; negative counts back from the end.
`length` optional	How many bytes to take; negative leaves that many off the end; `null` takes the rest.

The extracted part, or "" when the offset is past the end.

Take part of a stringTry it yourself

<?php
$text = "ReadyCamel";
echo substr($text, 0, 5), "\n";
echo substr($text, 5), "\n";
echo substr($text, -5, 3), "\n";

Output

Ready
Camel
Cam

Ends of a stringTry it yourself

<?php
$file = "invoice-2026.pdf";
echo substr($file, -3), "\n";   // extension
echo substr($file, 0, -4), "\n"; // drop it

Output

pdf
invoice-2026

Past the endTry it yourself

<?php
var_dump(substr("abc", 10));

Output

string(0) ""

Positions are bytes: substr("café", 0, 4) cuts é in half. Use mb_substr() for UTF-8 text.
To get a file's extension, pathinfo($file, PATHINFO_EXTENSION) handles names without a dot.

Version	Change
PHP 4.0	Added
PHP 8.0	Returns an empty string instead of `false` when the offset is past the end.

mb_substr() · Return part of a string by character position, so multibyte characters are never cut in half. The UTF-8 version of substr().
substr_replace() · Replace part of a string, given a start position and length, with another string. Also inserts text or masks digits.
strpos() · Find the position of the first occurrence of a substring. Returns false if it's not found, so compare with === false.
str_split() · Split a string into an array of chunks of a given length, one byte each by default. Use mb_str_split() for UTF-8.
PHP Strings · tutorial

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