Cookbooks
PHP
Chapter 9. Testing and Debugging
Printing debug output

PHP:
Printing debug output

How to: 

<?php
// Basic output
$variable = 'Debugging rocks!';
echo $variable;

// Using print_r for arrays
$myArray = ['apple', 'orange', 'banana'];
echo '<pre>'; // Makes it readable
print_r($myArray);
echo '</pre>';

// var_dump for details
$anotherArray = ['key' => 'value', 'anotherKey' => 123];
var_dump($anotherArray);

// To the error log
error_log('This goes to the logs for stealthier debugs.');
?>

Sample Output:

Debugging rocks!
Array
(
    [0] => apple
    [1] => orange
    [2] => banana
)
array(2) {
  ["key"]=>
  string(5) "value"
  ["anotherKey"]=>
  int(123)
}

Deep Dive:

Debug output hasn’t changed much: it’s been there since the early days when ancient programmers debugged with printf(). PHP embraced this with echo, print, print_r(), and var_dump(). It might not be fancy, but it works. Modern PHP devs also have Xdebug, which can step through code and show a fancier output. For logs, you’ve got error_log(), which sneaks messages into server logs without exposing them to users. Each tool has its place: echo and print are quick and dirty; print_r() is for human-friendly array insights; var_dump() gives you the nitty-gritty on types and lengths; error_log() keeps things under wraps when you’re in detective mode on a live site.

See Also:

Using an interactive shell (REPL)