io.close
io.flush
io.input
io.lines
io.open
io.output
io.open
io.read
io.tmpfile
io.type
io.write
file:close
file:flush
file:lines
file:read
file:seek
file:setvbuf
file:write
io - input and output facilities (standard 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 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.
io.close
io.close ([file])
Equivalent to file:close()
. Without a file
, closes the default
output file.
io.flush
io.flush ()
Equivalent to file:flush over the default output file.
io.input
io.input ([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.
io.lines
io.lines ([filename])
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.
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.
io.open
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.</li>
The mode
string may 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
.
io.output
io.output ([file])
Similar to io.input
, but operates over the default output file.
io.open
io.popen (prog [, mode])
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.
io.read
io.read (...)
Equivalent to io.input():
read.
io.tmpfile
io.tmpfile ()
Returns a handle for a temporary file. This file is opened in update mode and it is automatically removed when the program ends.
io.type
io.type (obj)
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.
io.write
io.write (...)
Equivalent to io.output():
write.
file:close
file:close ()
Closes file
. Note that files are automatically closed when their
handles are garbage collected, but that takes an unpredictable amount
of time to happen.
file:flush
file:flush ()
Saves any written data to file
.
file:lines
file:lines ()
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.)
file:read
file:read (...)
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
"*n"
"*a"
"*l"
nil
on end of file. This is the default format.
nil
on end of file. If number is zero, it reads nothing and
returns an empty string, or nil
on end of file.
file:seek
file:seek ([whence] [, offset])
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:
"set"
"cur"
"end"
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 "cur"
, and for offset
is 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
file:setvbuf (mode [, size])
Sets the buffering mode for an output file. There are three available modes:
"no"
"full"
flush
the file (see io.flush
)).
"line"
For the last two cases, sizes
specifies the size of the buffer, in
bytes. The default is an appropriate size.
file:write
file:write (...)
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
.
This is Lua version 5.1.1.
Lua is developed at Lua.org, a laboratory of the Department of Computer Science of PUC-Rio (the Pontifical Catholic University of Rio de Janeiro in Brazil). For more information about the authors, see http://www.lua.org/authors.html .
Lua is licensed under the terms of the MIT license reproduced below. This means that Lua is free software and can be used for both academic and commercial purposes at absolutely no cost.
For details and rationale, see http://www.lua.org/license.html .
~~~~~
Copyright (C) 1994-2006 Lua.org, PUC-Rio.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the ``Software''), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED ``AS IS'', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
~~~~~