Bridge - Arduino Sketches: Tools and Techniques for Programming Wizardry - page 367

used to perform read-and-write functions. If the i le cannot be opened, the File
object evaluates to false ; it is therefore possible to test if the i le was opened:
File datafile = FileSystem.open("/data/log.txt", FILE_WRITE);
if (!datafile)
Serial.println("ERROR: File could not be opened!");
File operations are exactly like the SD-card library; functions such as read() ,
write() , seek() , and flush() exist. This library is similar in structure to the
SD library; only the underlying routines change. For more information, see
Chapter 12.
However, not every function works on i les. open() requires a folder to exist,
but it does not work if the folder does not exist and does not create a folder if
it is missing. To remedy this, various i lesystem instructions exist that do not
require a i le to perform actions.
To check if a i le exists without opening it (or creating a new one), use exists() :
result = FileSystem.exists(filename);
The filename parameter is a String and is in the same format as open() . It
returns a boolean : true if the i le (or folder) exists and false if it does not exist.
To create a folder, use mkdir() :
result = FileSystem.exists(filename);
This function returns a boolean : true if the folder were created, false
otherwise. To delete a folder, use rmdir() :
result = FileSystem.rmdir(folder);
This function returns a boolean : true if the folder were deleted, false if the
function were unable to delete the folder. It requires the target folder to be empty;
any i les present must be removed. To remove i les, use remove() :
result = FileSystem.remove(filename);
This function, like the previous functions, returns a boolean : true if deleted,
false otherwise. This function is a wrapper for the system command rm and
as such can delete both i les and folders.
YunSer ver
The YunServer class is used when creating a server on the Arduino Yún's Linux
distro. This allows the Arduino side of the Yún to receive requests and to answer
those requests.
To create a server, you must i rst create a YunServer object:
YunServer server;
When the object has been created, you must tell the Arduino who can con-
nect. Contrary to most Arduino Ethernet shields, you will not want external