How to extract part of a string in PHP with substr()

Introduction

Use substr() when you need to extract part of a string in PHP.

echo substr('Laravel', 0, 4);
// Lara

The function is simple once you know what the three arguments mean:

• the string you start from
• the offset where extraction begins
• the optional length

The confusing parts are usually negative offsets, negative lengths, and multibyte strings like café or こんにちは. That is what this guide focuses on.

How to use substr() in PHP

The signature looks like this:

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

What each argument does:

• $string: the original string
• $offset: where to start
• $length: how many characters to keep

If you omit the length, substr() returns everything from the offset to the end of the string.

Basic substr() examples

Get the first few characters

echo substr('Laravel', 0, 4);
// Lara

Start at position 0 and keep 4 characters.

Get everything after a position

echo substr('Laravel', 4);
// vel

This is useful when you know where the interesting part begins and you want the rest of the string.

Start from the end with a negative offset

echo substr('Laravel', -3);
// vel

A negative offset counts backward from the end of the string.

Negative lengths and offsets

This is where most articles get vague. These are the rules that matter in practice.

Negative offset: start from the end

echo substr('Laravel', -4, 3);
// ave

-4 means “start four characters from the end.”

Negative length: stop before the end

echo substr('Laravel', 0, -1);
// Larave

A negative length tells PHP to leave characters off the end.

That makes substr() handy when you want to remove a file extension, trim a known suffix, or drop the last separator after building a string.

When the range does not make sense

var_dump(substr('Laravel', 2, -20));
// string(0) ""

If the requested slice falls outside the real string boundaries, PHP returns an empty string.

Common edge cases

Offset beyond the end returns an empty string

var_dump(substr('Laravel', 20));
// string(0) ""

This is not an error. You just get an empty string back.

Length longer than the remaining string is fine

echo substr('Laravel', 2, 20);
// ravel

PHP stops at the end of the string. It does not pad the result.

substr() can return an empty string, not false

In current PHP, a lot of old examples still talk about false here. For ordinary string slicing, what you will usually see is an empty string when nothing can be extracted.

That means === '' is often the check you want if an empty result matters in your code.

substr() vs mb_substr()

This is the most important practical warning in the whole article.

substr() works on bytes, not user-visible characters. That is fine for plain ASCII text, but it breaks multibyte UTF-8 strings.

ASCII works as expected

echo substr('Laravel', 0, 3);
// Lar

Multibyte text can break

var_dump(substr('café', 0, 4));
var_dump(mb_substr('café', 0, 4));
// string(4) "caf�"
// string(5) "café"

The same problem shows up even more clearly with non-Latin scripts:

var_dump(substr('こんにちは', 0, 3));
var_dump(mb_substr('こんにちは', 0, 3));
// string(3) "こ"
// string(9) "こんに"

If the input can contain UTF-8 text that users actually read, mb_substr() is usually the safer default.

Practical examples

Remove a known file extension

$filename = 'report.pdf';
echo substr($filename, 0, -4);
// report

This works because .pdf is four characters long.

Get the last part of a slug or identifier

$slug = 'laravel-forge';
echo substr($slug, -5);
// forge

Extract a prefix for quick matching

$code = 'INV-2026-0042';
echo substr($code, 0, 3);
// INV

If your next step is checking whether that prefix exists rather than extracting it, this string contains guide is the better fit.

substr() vs related functions

• Use substr() when you already know the position you want to cut at.
• Use strpos() when you first need to find the position of something.
• Use explode() when you are splitting by a separator.
• Use str_replace() when you want to replace part of the string instead of extracting it.

That keeps the code easier to read because each function has one clear job.

Conclusion

substr() is the right tool when you need part of a string and you already know the offset. The main things to remember are that negative offsets count from the end, negative lengths stop before the end, and UTF-8 text is where mb_substr() usually becomes the safer choice.

If you are still working through string handling after this, these are the next reads I would keep open:

• Check whether a string contains something without the old strpos() bug
• Split strings into arrays when a separator matters
• Join pieces back into one string cleanly