Input
io.read() can be used for standard input:
s = io.read() -- read a line
s = io.read("*l") -- read a line (default when no parameter is given)
s = io.read("*n") -- read a number
s = io.read("*a") -- read the complete stdin
s = io.read(7) -- read 7 characters from stdin
x,y = io.read(7,12) -- read 7 and 12 characters from stdin and assign them to x and y
a,b = io.read("*n","*n") -- read two numbers and assign them to a and b
Output
io.write() or io.stdout:write() can be used for standard output:
io.write("boo!")
Standard error
io.stderr:write() can be used to write to standard error.