Lua io standard library
Version: beta
Functions
io.close()
io.close([file])
Equivalent to
file:close().
Without a file, closes the default output file.
PARAMETERS
io.flush()
io.flush()
Equivalent to
file:flush over the default output file.
PARAMETERS
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.
PARAMETERS
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() (with no 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.
PARAMETERS
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.
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.
PARAMETERS
io.output()
io.output([file])
Similar to io.input, but operates over the default output file.
PARAMETERS
io.popen()
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.
PARAMETERS
io.read()
io.read(...)
Equivalent to
io.input():read.
PARAMETERS
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.
PARAMETERS
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.
PARAMETERS
io.write()
io.write(...)
Equivalent to
io.output():write.
PARAMETERS
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.
PARAMETERS
file:flush()
file:flush()
Saves any written data to file.
PARAMETERS
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.)
PARAMETERS
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"
- reads a number;
this is the only format that returns a number instead of a string.
- "*a"
- reads the whole file, starting at the current position.
On end of file, it returns the empty string.
- "*l"
- reads the next line (skipping the end of line),
returning nil on end of file.
This is the default format.
- number
- reads a string with up to this number of characters,
returning nil on end of file.
If number is zero,
it reads nothing and returns an empty string,
or nil on end of file.
PARAMETERS
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"
- base is position 0 (beginning of the file);
- "cur"
- base is current position;
- "end"
- base is end of file;
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.
PARAMETERS
file:setvbuf()
file:setvbuf(mode,[size])
Sets the buffering mode for an output file.
There are three available modes:
- "no"
- no buffering; the result of any output operation appears immediately.
- "full"
- full buffering; output operation is performed only
when the buffer is full (or when you explicitly
flush the file
).
- "line"
- line buffering; output is buffered until a newline is output
or there is any input from some special files
(such as a terminal device).
For the last two cases, size
specifies the size of the buffer, in bytes.
The default is an appropriate size.
PARAMETERS
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.
PARAMETERS