How to share data between two Lua scripts

(this method is a combination of @Puzzlem00n's suggestion and reading the comments, so I shouldn't take much credit from this at all)

Putting multiple games in one lua program!

In main.lua:

require("spaceInvaders") --require all the other Lua files
-- without the ".lua" at the end!

gamestate=spaceInvaders

function love.load()
--all the setup things
end

function love.update()
 gamestate.update()
end

function love.draw()
 gamestate.draw()
end

function love.keypressed(key)
 gamestate.keypressed(key)
end

--and so on for the rest of the love callbacks that you need (such as love.keyreleased())

Then in each game (which is a separate Lua file such as spaceInvaders.lua):

spaceInvaders = {}

function spaceInvaders.draw()
 --your draw code
end

function spaceInvaders.update()
 --your update code
end

--and so on for every other callback you want to use

What this code does is it gives each game its own set of love functions. When you want to play that game, you should set gamestate to that game's name. The spaceInvaders={} line defines spaceInvaders as a table, which stores each function in place. When you define a variable as an existing variable, you are actually creating a reference to it, for example:

t = {}
table.insert(t,1) --place 1 inside t
table.insert(t,3) --also place 3 inside t
s = t
print(s[1]) --will print 1, the first value of t
t[1]=2
print(s[1]) --will print 2, as it refers to t[1], which has just been changed

Sharing variables! (I worked out this bit!)

NOW, this means you can send variables around the program with another function. If you want to share score between games, you could do the following:

in main.lua:

function love.update()
 gamestate.update()
 score = gamestate.returnScore() --score will always equal to the current score being returned by the game
end

in a game, such as spaceInvaders.lua:

function spaceInvaders.returnScore()
 return score --or whatever the score is stored in
end

This will allow you to get a variable, such as score, from one game to main.lua! I'm sorry if this is a little confusing but hopefully this is what you're looking for! :)