|parrotcode: Lua Input/Output Library|
|Contents | Language Implementations | Lua|
lib/luaio.pir - Lua Input/Output Library
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 those default files. The second style uses explicit file descriptors.
When using implicit file descriptors,
all operations are supplied by table
When using explicit file descriptors,
io.open returns a file descriptor and then all operations are supplied as methods by the file descriptor.
io also provides three predefined file descriptors with their usual meanings from C:
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.
See "Lua 5.1 Reference Manual", section 5.7 "Input and Ouput Facilities".
file:close(). Without a
file, closes the default output file.
file:flushover the default output file.
for line in io.lines(filename) do ... end
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.
io.open (filename [, mode])
mode. It returns a new file handle, or, in case of errors, nil plus an error message.
modestring can be any of the following:
modestring may also have a
bat the end, which is needed in some systems to open the file in binary mode. This string is exactly what is used in the standard C function
io.input, but operates over the default output file.
io.popen ([prog [, mode]])
progin a separated process and returns a file handle that you can use to read data from this program (if
"r", the default) or to write data to this program (if
io.read (format1, ...)
objis a valid file handle. Returns the string
objis an open file handle,
objis a closed file handle, and nil if
objis not a file handle.
io.write (value1, ...)
file. Note that files are automatically closed when their handles are garbage collected, but that takes an unpredictable amount of time to happen.
for line in file:lines() do ... end
io.lines, this function does not close the file when the loop ends.)
file:read (format1, ...)
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).
file:seek ([whence] [, offset])
offsetplus a base specified by the string
whence, as follows:
seekreturns the final file position, measured in bytes from the beginning of the file. If this function fails, it returns nil, plus a string describing the error.
"cur", and for
offsetis 0. Therefore, the call
file:seek()returns the current file position, without changing it; the call
file:seek("set")sets the position to the beginning of the file (and returns 0); and the call
file:seek("end")sets the position to the end of the file, and returns its size.
file:setvbuf (mode [, size])
file:write (value1, ...)
file. The arguments must be strings or numbers. To write other values, use