The io module provides input/output functionality, including reading from and writing to files, pipes, and the standard input/output/error streams.

io.stdin

io.stdin

The io.stdin file represents the standard input stream. It can be used to read input from the user.

Example

import io

// Read a line of input from the user
var str = io.stdin.readline()
print(str)

io.stdout

io.stdout

The io.stdout file represents the standard output stream. It can be used to write output text to the console.

Example

import io

// Print a string to the console
io.stdout.write("Hello, world!")    // Hello, world!

io.stderr

io.stderr

The io.stderr file represents the standard error stream. It can be used to write error messages to the console.

Example

import io

// Print an error message to the console
io.stderr.write("An error occurred!")  // An error occurred!

io.open()

function io.open(path, mode='r')

The open function opens a file at the specified path with the given mode.

Arguments

  • path: The path to the file to open.
  • mode: An optional string specifying the mode in which to open the file. Defaults to "r".

Example

import io

// Open a file for reading
var file = io.open("data.txt", "r")

// Open a file for writing
var output = io.open("output.txt", "w")

// Open a file for appending
var log = io.open("log.txt", "a")

io.popen()

function io.popen(path, mode='r')

The popen function opens a pipe to a subprocess command.

Arguments

  • path: The command to execute.
  • mode: An optional string specifying the mode in which to open the pipe. Defaults to "r".

Example

import io

// Open a pipe to read from a command
var pipe = io.popen("ls -la", "r")
var content = pipe.read()
print(content)

File

The File class represents an open file handle returned by io.open, io.popen, or the standard streams:

  • io.stdout
  • io.stdin
  • io.stderr

File:write()

function File:write(...)

The write method writes one or more values to the file.

Arguments

  • ...: One or more values to write to the file.

Example

import io

var file = io.open("output.txt", "w")
file.write("Hello, world!\n")
file.write("Line 2\n")
file.write("Value: ", 42, "\n")
file.close()

File:read()

function File:read(count=nil)

The read method reads data from the file. When called with no arguments, it reads the entire file content. When called with a count argument, it reads up to count bytes.

Arguments

  • count: An optional number of bytes to read. If not specified, the entire file is read.

Example

import io

var file = io.open("data.txt", "r")

// Read the entire file
var content = file.read()
print(content)

// Read a specific number of bytes
file.seek("set", 0)
var first_10 = file.read(10)
print(first_10)

file.close()

File:readline()

function File:readline()

The readline method reads a single line from the file.

Arguments

The method takes no arguments.

Example

import io

var file = io.open("data.txt", "r")
var line = file.readline()
while line != nil
{
    print(line)
    line = file.readline()
}
file.close()

File:seek()

function File:seek(whence='cur', offset=0)

The seek method moves the file position indicator to a new location.

Arguments

  • whence: An optional string specifying the reference point for the offset. Can be "set", "cur", or "end". Defaults to "cur".
  • offset: An optional number specifying the number of bytes to move from the reference point. Defaults to 0.

Example

import io

var file = io.open("data.txt", "r")

// Move to the beginning of the file
var pos = file.seek("set", 0)
print("Position:", pos)

// Move forward 10 bytes from current position
pos = file.seek("cur", 10)
print("Position:", pos)

// Move to 5 bytes before the end of the file
pos = file.seek("end", -5)
print("Position:", pos)

file.close()

File:flush()

function File:flush()

The flush method flushes any buffered data to the file.

Arguments

The method takes no arguments.

Example

import io

var file = io.open("output.txt", "w")
file.write("Important data")
file.flush()  // Ensure data is written to disk immediately

File:setvbuf()

function File:setvbuf(mode, size=8192)

The setvbuf method sets the buffering mode for the file.

Arguments

  • mode: A string specifying the buffering mode. Can be "full", "line", or "no".
  • size: An optional number specifying the buffer size in bytes. Defaults to 8192.

Example

import io

var file = io.open("output.txt", "w")

// Set line buffering
file.setvbuf("line")

// Set no buffering
file.setvbuf("no")

// Set full buffering with a custom size
file.setvbuf("full", 4096)

File:close()

function File:close()

The close method closes the file. Standard streams cannot be closed.

Arguments

The method takes no arguments.

Example

import io

var file = io.open("data.txt", "r")
var content = file.read()
file.close()

File:tostring()

function File:tostring()

The tostring method provides a string representation of the file object.

Arguments

The method takes no arguments.

Example

import io

var file = io.open("data.txt", "r")
print(file.tostring())  // <file>
file.close()
print(file.tostring())  // <file (closed)>

File:iter()

function File:iter()

The iter method provides an iterator that reads lines from the file one at a time.

Arguments

The method takes no arguments.

Example

import io

var file = io.open("data.txt", "r")
for const line in file.iter()
{
    print(line)
}
file.close()