PHP chunk_split() Function

What You’ll Learn

The chunk_split() function splits a string into fixed-size pieces and inserts a separator after each piece. It returns one formatted string—perfect for wrapping long lines in email bodies, displaying hex data, or breaking text into readable blocks.

Definition and Usage

In PHP, chunk_split() walks through a string from left to right, taking $length characters at a time and appending the $separator after each group. For example, splitting "HelloWorld123" into chunks of 4 with "-" produces Hell-oWor-ld12-3-.

📝 Syntax

The chunk_split() function accepts up to three parameters:

string chunk_split(string $string, int $length = 76, string $separator = "\r\n")

Parameters

• $string — the input string to split into chunks.
• $length (optional) — maximum characters per chunk. Default: 76.
• $separator (optional) — string inserted after each chunk. Default: "\r\n" (carriage return + line feed).

Return Value

Returns a new string with chunks and separators combined. The original string is not modified.

Examples Gallery

Run these examples in any PHP 7+ environment. Each one demonstrates a common pattern beginners encounter with chunk_split().

<?php
$input       = "HelloWorld123";
$chunked     = chunk_split($input, 4, "-");

echo $chunked . "\n";
echo "Length: " . strlen($chunked) . "\n";
?>

Hell-oWor-ld12-3-
Length: 17

<?php
$data = str_repeat("A", 80);  // 80-character string
$wrapped = chunk_split($data);

$lines = explode("\r\n", trim($wrapped));
echo "Total lines: " . count($lines) . "\n";
echo "Line 1 length: " . strlen($lines[0]) . "\n";
echo "Line 2 length: " . strlen($lines[1]) . "\n";
?>

Total lines: 2
Line 1 length: 76
Line 2 length: 4

<?php
$cardNumber = "4111111111111111";
$display    = rtrim(chunk_split($cardNumber, 4, " "), " ");

echo $display . "\n";
?>

4111 1111 1111 1111

<?php
$text = "PHP8Rock";

echo "chunk_split:\n";
echo chunk_split($text, 3, "|") . "\n";

echo "str_split:\n";
print_r(str_split($text, 3));
?>

chunk_split:
PHP|8Ro|ck|

str_split:
Array
(
    [0] => PHP
    [1] => 8Ro
    [2] => ck
)

<?php
$raw  = "CodeToFun";
$hex  = bin2hex($raw);
$pretty = rtrim(chunk_split($hex, 8, " "), " ");

echo "Raw:    $raw\n";
echo "Hex:    $hex\n";
echo "Pretty: $pretty\n";
?>

Raw:    CodeToFun
Hex:    436f6465546f46756e
Pretty: 436f6465 546f4675 6e

🚀 Common Use Cases

• MIME email encoding — wrap Base64 attachment data at 76 characters per line.
• Readable number groups — format long IDs, phone numbers, or card numbers for display.
• Hex and hash output — space-separate long hexadecimal strings in debug logs.
• Protocol formatting — insert line breaks in fixed-width text payloads.
• Teaching string manipulation — understand chunking before learning arrays and loops.

📝 Notes

• The separator is appended after every chunk, including the last partial one.
• Use rtrim($result, $separator) if you need to remove a trailing separator.
• Default length 76 and separator \r\n target email/MIME compatibility.
• For an array of chunks, use str_split($string, $length) instead.
• Chunk length must be at least 1; passing 0 or negative values causes errors in PHP 8+.

💡 Best Practices