PHP: Cut string using last character searched

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/**
    * Taken from: http://php.net/manual/en/function.strrchr.php
    *
     * Removes the preceeding or proceeding portion of a string
     * relative to the last occurrence of the specified character.
     * The character selected may be retained or discarded.
     *
     * Example usage:
     * <code>
     * $example = 'http://example.com/path/file.php';
     * $cwd_relative[] = cut_string_using_last('/', $example, 'left', true);
     * $cwd_relative[] = cut_string_using_last('/', $example, 'left', false);
     * $cwd_relative[] = cut_string_using_last('/', $example, 'right', true);
     * $cwd_relative[] = cut_string_using_last('/', $example, 'right', false);
     * foreach($cwd_relative as $string) {
     *     echo "$string <br>".PHP_EOL;
     * }
     * </code>
     *
     * Outputs:
     * <code>
     * http://example.com/path/
     * http://example.com/path
     * /file.php
     * file.php
     * </code>
     *
     * @param string $character the character to search for.
     * @param string $string the string to search through.
     * @param string $side determines whether text to the left or the right of the character is returned.
     * Options are: left, or right.
     * @param bool $keep_character determines whether or not to keep the character.
     * Options are: true, or false.
     * @return string
     */
    function cut_string_using_last($character, $string, $side, $keep_character=true) {
        $offset = ($keep_character ? 1 : 0);
        $whole_length = strlen($string);
        $right_length = (strlen(strrchr($string, $character)) - 1);
        $left_length = ($whole_length - $right_length - 1);
        switch($side) {
            case 'left':
                $piece = substr($string, 0, ($left_length + $offset));
                break;
            case 'right':
                $start = (0 - ($right_length + $offset));
                $piece = substr($string, $start);
                break;
            default:
                $piece = false;
                break;
        }
        return($piece);
    }