PHP substr Function: How to Extract and Manipulate Strings

The substr() function in PHP returns part of a string. You give it a string, a starting point, and optionally a length. It cuts the string based on those numbers and gives you the piece you asked for.

Understand the substr Function in PHP

You use substr() when you need to pull out a part of a string. Maybe you want just the first few letters. Maybe you need everything after a certain point. It works well when you know the position of the part you want.

Here is the full syntax for substr():

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

Here, what each part does.

• $string
  This is the full string you want to work with. It can be any string.
• $start
  This tells PHP where to start cutting. The count starts from 0. If you use a negative number, PHP counts from the end of the string.
• $length (optional)
  This tells PHP how many characters to return. If you leave it out, PHP gives you everything from the start point to the end of the string. If the number is negative, PHP will stop that many characters from the end.

A Quick example:

$text = "Welcome to flatcoding tutorials";
echo substr($text, 0, 7); 

Output:

Welcome

PHP starts at index 0 and returns the next 7 characters.

You can also use a negative start value:

echo substr($text, -20);

This starts 20 characters from the end and goes to the end of the string. Its output:

flatcoding tutorials

Examples of the substr Function in PHP

Multibyte strings:

If you work with non-English characters like Japanese, Arabic, or emojis, substr() might not work correctly. That is because substr() counts bytes, not full characters.

$text = "こんにちは"; // Japanese
echo substr($text, 0, 3); // Broken output: こ

This function works on standard strings. For multibyte support, see other PHP functions.

Mix substr() with another string:

You can mix substr() with other string functions. Here is an example:

$email = "[email protected]";
$domain = substr(strrchr($email, "@"), 1);
echo $domain; 

The output:

example.com

This first finds the @ and then cuts the domain part.

Extracting file extensions:

You can get a file extension like this:

$file = "photo.jpg";
$ext = substr($file, strrpos($file, '.') + 1);
echo $ext; 

The output:

jpg

Wrapping Up

substr() gives you control over string parts based on position and length. It is simple, fast, and useful for many cases.

Here is a quick recap:

• substr() returns part of a string with a start position and optional length.
• Use positive or negative numbers to control where it starts and how much it returns.
• If you leave out the length, PHP gives everything from the start to the end.
• substr() works well to truncate text and slice values. Also to clean user input.
• If the start index is too big, PHP returns an empty string.
• If the length is too large, PHP stops at the end of the string.
• Don’t use substr() inside loops unless needed.

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