Openfile

io.open (filename [, mode])

This function opens a file, in the mode specified in the string mode. It returns a new file handle, or, in case of errors, nil plus an error message.

The mode string can be any of the following:

• "r": read mode (the default);
• "w": write mode;
• "a": append mode;
• "r+": update mode, all previous data is preserved;
• "w+": update mode, all previous data is erased;
• "a+": append update mode, previous data is preserved, writing is only allowed at the end of file.

• "b": the mode string can also have a 'b' at the end, which is needed to open the file in binary mode.

This string is exactly what is used in the standard C function fopen.

mode			description	starts..
r	rb		open for reading	beginning
w	wb		open for writing (creates file if it doesn't exist). Deletes content and overwrites the file.	beginning
a	ab		open for appending (creates file if it doesn't exist)	end
r+	rb+	r+b	open for reading and writing	beginning
w+	wb+	w+b	open for reading and writing. Deletes content and overwrites the file.	beginning
a+	ab+	a+b	open for reading and writing (append if file exists)	end