The io.read() function is used to read data from the file on SD card.
Notice: other read commands (like "all", etc..) are *not supported.
file object
a file object that was returned by the io.open() function. The file must be opened in read mode.
length
number of characters/bytes to read. The number of actual read/returned characters can be less if the file end is reached.
<string>
a string with a length equal or less than
""
a zero length string if the end of file was reached