So far we know how to print to standard out using the print function.
Now I'm going to talk about two functions in the standard library called
io.read and io.write.
io is a table.
It's a table that has some functions as some of its values.
It's part of the standard library, and if you're using Lua from an embedded app, such as a game, the developers may have chosen to exclude some of the modules of the standard library - or all of them - for security reasons, probably. So it's not guaranteed that you have access to these functions. By default, such as in the interpreter, you do have access to these functions.
I'm going to tell you about them since they're very useful.
The default action of io.read is to read a line from standard in.
The return value is the string with the line. However, it excludes the newline character at the end of the line.
> line = io.read()
hi -- Editor's note: the string "hi<enter>" is user-typed.
> = line
hi
> = #line
2
You can also use io.read by giving it a number parameter.
This asks io.read to read up to that many characters from standard in.
> s = io.read(4)
abcdefghi -- User-typed.
As you can see in this example,
the variable s will have 4 characters.
> = s
abcd
io.write acts similarly to print.
I'll give it a string as input here:
> s = 'hallo\n'
> io.write(s)
hallo
One thing that's interesting is that the string contained a
newline. io.write did not add a newline - that's the way
io.write behaves.
print, on the other hand, if I give it the same string, will
add a newline:
> print(s)
hallo!
> -- Editor's note: the next Lua prompt is here.
io.write also accepts multiple parameters.
If it takes a number as an input, then it converts that to a string;
otherwise it only accepts strings.
It concatenates multiple parameters together without any spaces
between them, and never adds a newline at the end, like that:
> io.write('pi is ', 'close to ', 3.14)
pi is close to 3.14> -- Editor's note: the > is Lua's input prompt.