print_r()

Introduction

print_r() is a built-in PHP function that prints a human-readable representation of a variable. For scalars (strings, numbers, booleans) it simply prints the value, but its real value is with arrays and objects: it lays out the keys and values as an indented tree, so you can see the structure at a glance.

It is one of the three go-to debugging functions in PHP, alongside var_dump() and var_export(). Reach for print_r() when you want a quick, readable look at what's inside a variable.

Syntax

print_r(mixed $value, bool $return = false): string|true

The return value depends on $return: with the default false it returns true; with true it returns the formatted string.

Printing an array

print_r() shows nested arrays as an indented tree, which makes it easy to read multi-level data:

Each key appears as [key] => value, and the nested roles array is indented under its parent:

Array
(
    [name] => Alice
    [age] => 30
    [roles] => Array
        (
            [0] => admin
            [1] => editor
        )

)

Capturing the output as a string

Pass true as the second argument to return the formatted text instead of printing it. This is handy for writing the structure to a log file, embedding it in an error message, or wrapping it in HTML:

<?php
$data = ["x" => 1, "y" => 2];

$text = print_r($data, true);   // captured, not printed
error_log($text);               // e.g. send it to the log

echo strtoupper(substr($text, 0, 5)); // prints: ARRAY
?>

Tip: wrap it in <pre> for the browser

In a web page, browsers collapse the indentation and newlines that print_r() relies on, so the output looks like one run-on line. Wrap it in a <pre> tag (or capture with $return and echo inside <pre>) to keep the formatting readable:

<?php
echo "<pre>";
print_r($person);
echo "</pre>";
?>

print_r() vs. var_dump() vs. var_export()

These three functions all inspect variables, but they serve different needs:

• print_r() — the most readable. Best for a quick human-eye check of structure. It does not show data types or string lengths.
• var_dump() — shows the type and size of every value (int(30), string(5) "Alice"), and can print several variables at once. Best when the type matters (e.g. distinguishing 0, "0", false, and null).
• var_export() — outputs valid PHP code that recreates the variable. Best when you want a value you can paste back into source or cache.

If you only need to know what type a single variable is, gettype() is more direct.

Conclusion

print_r() is the friendliest of PHP's inspection tools: it prints arrays and objects as a clean, indented tree that's easy to scan while debugging. Use the default mode to dump a variable straight to the output, pass true to capture the result as a string, and wrap the call in <pre> when you're viewing it in a browser. When you also need types and sizes, switch to var_dump(); when you need reusable PHP code, use var_export().

Practice