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Editorial Team
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Asked: 2026-05-18T23:17:05+00:00

I’ve seen a lot of PHP code that handles form input in which the

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I’ve seen a lot of PHP code that handles form input in which the input field names contain square brackets. I understand that this somehow results in PHP arrays when a PHP script examines the $_POST variable.

Example HTML:

<form action='http://zzz.com' method='post'>
    <input name='fruit[1]' value='apple' />
    <input name='fruit[2]' value='banana' />
</form>

Example URL:

http://zzz.com?fruit[1]=apple&fruit[2]=banana

Example PHP:

assert($_POST['fruit'] === array(1=>'apple', 2=>'banana'));

My questions about this:

  • What is the mechanism behind it? At what point do these names that contain brackets get converted into arrays? Is this a feature of the HTTP protocol? Of web servers? Of the PHP language?

  • Continuing the previous question, is this a commonly used hack or a normal programming tool?

  • What are (all) the rules for using brackets in input field names?

  • Can multidimensional arrays be created this way?

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1 Answer

  1. Editorial Team

    What is the mechanism behind? At which
    point this names that merely contain
    brackets are converted to arrays? Is
    this a feature of the HTPP protocol?
    Of web servers? Of the PHP language?>

    This is a feature of the PHP language. In fact, the HTTP protocol does not forbid the use of multiple identical GET/POST parameters. According to the HTTP spec, the following:

    foo=bar&foo=baz

    Should not result in foo == baz. These are two parameters with two different values. However, PHP will overwrite the former foo with the latest, resulting in $_POST['foo'] == 'baz', even if they could be parsed separately.

    Continuing the previous question, is
    this a commonly used hack or a normal
    programming tool?

    It depends on the point of view. In the PHP world, it is completely normal, as the language does not support the specification of multiple parameters of the same name without using the brackets []. In the HTTP world though, foo != foo[].

    What are (all) the rules of using
    brackets in input field names?

    The same as PHP arrays, except that you don’t have to quote string keys.

    Can multidimensional arrays be created
    this way?

    Yes, you can.

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