The I/O library provides two different styles for file manipulation. The first one uses implicit file descriptors; that is, there are operations to set a default input file and a default output file, and all input/output operations are over these default files. The second style uses explicit file descriptors.
When using implicit file descriptors, all operations are supplied by table io. When using explicit file descriptors, the operation io.open returns a file descriptor and then all operations are supplied as methods of the file descriptor.
The table io also provides three predefined file descriptors with their usual meanings from C: io.stdin, io.stdout, and io.stderr.
Unless otherwise stated, all I/O functions return nil on failure (plus an error message as a second result) and some value different from nil on success.
for line in file:lines() do ... endwill iterate over all lines of the file. (Unlike io.lines, this function does not close the file when the loop ends.)
Reads the file file, according to the given formats, which specify what to read. For each format, the function returns a string (or a number) with the characters read, or nil if it cannot read data with the specified format. When called without formats, it uses a default format that reads the entire next line (see below).
The available formats are
Sets and gets the file position, measured from the beginning of the file, to the position given by offset plus a base specified by the string whence, as follows:
Sets the buffering mode for an output file. There are three available modes:
When called with a file name, it opens the named file (in text mode), and sets its handle as the default input file. When called with a file handle, it simply sets this file handle as the default input file. When called without parameters, it returns the current default input file.
In case of errors this function raises the error, instead of returning an error code.Opens the given file name in read mode and returns an iterator function that, each time it is called, returns a new line from the file. Therefore, the construction
for line in io.lines(filename) do ... endwill iterate over all lines of the file. When the iterator function detects the end of file, it returns nil (to finish the loop) and automatically closes the file. The call io.lines() (without a file name) is equivalent to io.input():lines(); that is, it iterates over the lines of the default input file. In this case it does not close the file when the loop ends.
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:
Starts program prog in a separated process and returns a file handle that you can use to read data from this program (if mode is "r", the default) or to write data to this program (if mode is "w").
This function is system dependent and is not available on all platforms.