I like YAML:

root: '/path/to/root'
filepath: '/path/to/files'
ftp_instances:
  - sourcepath: '/source/path/on/server'
    savepath: '/save/files/here'
  - sourcepath: 
    savepath: 
  - sourcepath:
    savepath:
[download]

(Though, as noted, it is sensitive to whitespace, YAML returns nice error messages, including a program usable code, a human usable error message and the line number of any error.)

Reading that YAML file returns this perl structure:

$VAR1 = {
  'ftp_instances' => [
    {
      'savepath' => '/save/files/here',
      'sourcepath' => '/source/path/on/server'
    },
    {
      'savepath' => '',
      'sourcepath' => ''
    },
    {
      'savepath' => '',
      'sourcepath' => ''
    }
  ],
  'filepath' => '/path/to/files',
  'root' => '/path/to/root'
};
[download]