io

Emulates Lua's standard io library.

stdinA file handle representing the "standard input".
stdoutA file handle representing the "standard output".
stderrA file handle representing the "standard error" stream.
close([file])Closes the provided file handle.
flush()Flushes the current output file.
input([file])Get or set the current input file.
lines([filename, ...])Opens the given file name in read mode and returns an iterator that, each time it is called, returns a new line from the file.
open(filename [, mode])Open a file with the given mode, either returning a new file handle or nil, plus an error message.
output([file])Get or set the current output file.
read(...)Read from the currently opened input file.
type(obj)Checks whether handle is a given file handle, and determine if it is open or not.
write(...)Write to the currently opened output file.
stdinSource

A file handle representing the "standard input". Reading from this file will prompt the user for input.

stdoutSource

A file handle representing the "standard output". Writing to this file will display the written text to the screen.

stderrSource

A file handle representing the "standard error" stream.

One may use this to display error messages, writing to it will display them on the terminal.

close([file])Source

Closes the provided file handle.

Parameters

  1. file? Handle The file handle to close, defaults to the current output file.

See also

Changes

  • New in version 1.55
flush()Source

Flushes the current output file.

See also

Changes

  • New in version 1.55
input([file])Source

Get or set the current input file.

Parameters

  1. file? Handle | string The new input file, either as a file path or pre-existing handle.

Returns

  1. Handle The current input file.

Throws

  • If the provided filename cannot be opened for reading.

Changes

  • New in version 1.55
lines([filename, ...])Source

Opens the given file name in read mode and returns an iterator that, each time it is called, returns a new line from the file.

This can be used in a for loop to iterate over all lines of a file

Once the end of the file has been reached, nil will be returned. The file is automatically closed.

If no file name is given, the current input will be used instead. In this case, the handle is not used.

Parameters

  1. filename? string The name of the file to extract lines from
  2. ... The argument to pass to Handle:read for each line.

Returns

  1. function():string | nil The line iterator.

Throws

  • If the file cannot be opened for reading

Usage

  • Iterate over every line in a file and print it out.

    for line in io.lines("/rom/help/intro.txt") do
  print(line)
end

See also

Changes

  • New in version 1.55
open(filename [, mode])Source

Open a file with the given mode, either returning a new file handle or nil, plus an error message.

The mode string can be any of the following:

  • "r": Read mode
  • "w": Write mode
  • "a": Append mode

The mode may also have a b at the end, which opens the file in "binary mode". This allows you to read binary files, as well as seek within a file.

Parameters

  1. filename string The name of the file to open.
  2. mode? string The mode to open the file with. This defaults to rb.

Returns

  1. Handle The opened file.

Or

  1. nil In case of an error.
  2. string The reason the file could not be opened.
output([file])Source

Get or set the current output file.

Parameters

  1. file? Handle | string The new output file, either as a file path or pre-existing handle.

Returns

  1. Handle The current output file.

Throws

  • If the provided filename cannot be opened for writing.

Changes

  • New in version 1.55
read(...)Source

Read from the currently opened input file.

This is equivalent to io.input():read(...). See the documentation there for full details.

Parameters

  1. ... string The formats to read, defaulting to a whole line.

Returns

  1. string | nil... The data read, or nil if nothing can be read.
type(obj)Source

Checks whether handle is a given file handle, and determine if it is open or not.

Parameters

  1. obj The value to check

Returns

  1. string | nil "file" if this is an open file, "closed file" if it is a closed file handle, or nil if not a file handle.
write(...)Source

Write to the currently opened output file.

This is equivalent to io.output():write(...). See the documentation there for full details.

Parameters

  1. ... string The strings to write

Changes

  • Changed in version 1.81.0: Multiple arguments are now allowed.

Types

Handle

A file handle which can be read or written to.

Handle.close()Source

Close this file handle, freeing any resources it uses.

Returns

  1. true If this handle was successfully closed.

Or

  1. nil If this file handle could not be closed.
  2. string The reason it could not be closed.

Throws

  • If this handle was already closed.

Handle.flush()Source

Flush any buffered output, forcing it to be written to the file

Throws

  • If the handle has been closed

Handle.lines(...)Source

Returns an iterator that, each time it is called, returns a new line from the file.

This can be used in a for loop to iterate over all lines of a file

Once the end of the file has been reached, nil will be returned. The file is not automatically closed.

Parameters

  1. ... The argument to pass to Handle:read for each line.

Returns

  1. function():string | nil The line iterator.

Throws

  • If the file cannot be opened for reading

Usage

  • Iterate over every line in a file and print it out.

    local file = io.open("/rom/help/intro.txt")
for line in file:lines() do
  print(line)
end
file:close()

See also

Changes

  • New in version 1.3
Handle.read(...)Source

Reads data from the file, using the specified formats. For each format provided, the function returns either the data read, or nil if no data could be read.

The following formats are available:

  • l: Returns the next line (without a newline on the end).
  • L: Returns the next line (with a newline on the end).
  • a: Returns the entire rest of the file.
  • ~~n: Returns a number~~ (not implemented in CC).

These formats can be preceded by a * to make it compatible with Lua 5.1.

If no format is provided, l is assumed.

Parameters

  1. ... The formats to use.

Returns

  1. string | nil... The data read from the file.
Handle.seek([whence [, offset]])Source

Seeks the file cursor to the specified position, and returns the new position.

whence controls where the seek operation starts, and is a string that may be one of these three values:

  • set: base position is 0 (beginning of the file)
  • cur: base is current position
  • end: base is end of file

The default value of whence is cur, and the default value of offset is 0. This means that file:seek() without arguments returns the current position without moving.

Parameters

  1. whence? string The place to set the cursor from.
  2. offset? number The offset from the start to move to.

Returns

  1. number The new location of the file cursor.
Handle.setvbuf(mode [, size])Source
Deprecated

This has no effect in CC.

Sets the buffering mode for an output file.

This has no effect under ComputerCraft, and exists with compatility with base Lua.

Parameters

  1. mode string The buffering mode.
  2. size? number The size of the buffer.

See also

Handle.write(...)Source

Write one or more values to the file

Parameters

  1. ... string | number The values to write.

Returns

  1. Handle The current file, allowing chained calls.

Or

  1. nil If the file could not be written to.
  2. string The error message which occurred while writing.

Changes

  • Changed in version 1.81.0: Multiple arguments are now allowed.