function onFileClbk( file ) {
	return onFile;

	/**
	* Callback invoked upon reading a file.
	*
	* @private
	* @param {(Error|null)} error - error object
	* @param {(Buffer|string)} data - file data
	*/
	function onFile( error, data ) {
		if ( error ) {
			debug( 'Encountered an error when attempting to read file contents: %s', error.message );
			throw error;
		}
		debug( 'Successfully read file: %s', file );
		data = data.toString();

		debug( 'Converting file data to JSON.' );
		data = toJSON( file, data );

		writeFile( file, data+'\n' );
	}
}
Returns a callback to be invoked upon reading a file.

@private
@param {string} file - file name
@returns {Callback} callback