Module io
Reading and Writing Files.
Functions
| close (file) | Equivalent to `file:close()`. |
| flush () | Equivalent to `file:flush` over the default output file. |
| 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. |
| 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. |
| open (filename, mode) | This function opens a file, in the mode specified in the string `mode`. |
| output (file) | Similar to `io.input`, but operates over the default output file. |
| 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"`). |
| read (...) | Equivalent to `io.input():read`. |
| tmpfile () | Returns a handle for a temporary file. |
| type (obj) | Checks whether `obj` is a valid file handle. |
| write (...) | Equivalent to `io.output():write`. |
| file:close () | Closes `file`. |
| file:flush () | Saves any written data to `file`. |
| file:lines () | Returns an iterator function that, each time it is called, returns a new line from the file. |
| file:read (...) | Reads the file `file`, according to the given formats, which specify what to read. |
| 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. |
| file:setvbuf (mode, size) | Sets the buffering mode for an output file. |
| file:write (...) | Writes the value of each of its arguments to the `file`. |
Functions
- close (file)
-
Equivalent to `file:close()`. Without a `file`, closes the default
output file.
Parameters:
- file
- flush ()
- Equivalent to `file:flush` over the default output file.
- 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:
- file
- 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:
- filename
- 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:
- filename
- mode
- output (file)
-
Similar to `io.input`, but operates over the default output file.
Parameters:
- file
- 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:
- prog
- mode
- read (...)
-
Equivalent to `io.input():read`.
Parameters:
- ...
- tmpfile ()
- Returns a handle for a temporary file. This file is opened in update mode and it is automatically removed when the program ends.
- 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:
- obj
- write (...)
-
Equivalent to `io.output():write`.
Parameters:
- ...
- 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 ()
- Saves any written data to `file`.
- 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 (...)
-
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 (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:
- whence
- offset
- 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 (see `io.flush`)). * "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:
- mode
- size
- 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:
- ...