Lua io standard library
Documentation for the Lua io standard library.
From Lua 5.1 Reference Manual by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes.
Copyright © 2006-2012 Lua.org, PUC-Rio.
Freely available under the terms of the Lua license.
closes a filefile:flush
flushes outstanding data to diskfile:lines
returns an iterator function for reading the file line-by-linefile:read
reads the file according to the specified formatsfile:seek
sets and gets the current file positionfile:setvbuf
sets the buffering mode for an output filefile:write
writes to a fileio.close
closes a fileio.flush
flushes outstanding data to disk for the default output fileio.input
opens filename for input in text modeio.lines
returns an iterator function for reading a named file line-by-lineio.open
opens a fileio.output
opens a file for outputio.popen
creates a pipe and executes a commandio.read
reads from the default input fileio.tmpfile
returns a handle to a temporary fileio.type
returns type of file handleio.write
writes to the default output file
Closes file. Note that files are automatically closed when their handles are garbage collected, but that takes an unpredictable amount of time to happen.
Saves any written data to file.
Returns an iterator function that, each time it is called, returns a new line from the file. Therefore, the construction
for line in file:lines() do body end
will 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:
In case of success, function seek returns 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.
The default value for whence is
and for offset is 0.
Therefore, the call
file:seek() returns the current
file position, without changing it;
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.
Sets the buffering mode for an output file. There are three available modes:
flushthe file ).
For the last two cases, size specifies the size of the buffer, in bytes. The default is an appropriate size.
Writes the value of each of its arguments to the file. The arguments must be strings or numbers. To write other values, use tostring or string.format before write.
Without a file, closes the default output file.
file:flush over the default output file.
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 body end
will 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.
io.lines() (with no file name) is equivalent
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:
The mode string can also have a 'b' at 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 fopen.
Similar to io.input, but operates over the default output file.
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
This function is system dependent and is not available on all platforms.
Returns a handle for a temporary file. This file is opened in update mode and it is automatically removed when the program ends.
Checks whether obj is a valid file handle.
Returns the string
"file" if obj is an open file handle,
"closed file" if obj is a closed file handle,
or nil if obj is not a file handle.