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# array_keys

array_keys -- Return all the keys of an array

## Description

`array array_keys`(array input, mixed [search_value]);

array_keys() returns the keys, numeric and string, from the `input` array.

If the optional `search_value` is specified, then only the keys for that value are returned. Otherwise, all the keys from the `input` are returned.

Example 1. array_keys() example
    $array = array(0 => 100, "color" => "red");
    array_keys($array);       // returns array(0, "color")

    $array = array(1, 100, 2, 100);
    array_keys($array, 100); //  returns array(0, 2)

See also array_values().

> Note: This function was added in PHP 4.0.

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