Storing variables in a file

Say something… Hm…

Many have asked how to store variables in a file. And this is a basic tutorial about that. (You couldn't have been much more straightforward LBP, could you?)
This tutorial requires a basic knowledge of tables.

Step 1: Set up your variables inside a table

local health = 4
local hunger = 8
local armor = 3
local name = "Steve"

local target = {} -- this is a table
target.health = health
target.hunger = hunger
target.armor = armor
target.name = name

Step 2: Convert the table to a string

local output = textutils.serialize(target)

Step 3: Save the string to a file

local handle = assert(fs.open("vars", "w"), "Couldn't save vars") -- this will give you an error if something's gone wrong
handle.write(output) -- this is where the magic happens, we're storing the entire "target" table
handle.close()

We're done!
Now try to load that table.

Step 4: Read the serialized table

local handle = assert(fs.open("vars", "r"), "Couldn't load vars") -- this file is opened in read mode
local input = handle.readAll() -- input is now the serialized table
handle.close()

Step 5: Convert the string to a table

local destination = textutils.unserialize(input) -- this will decode our table

print(destination.health) -- prints 4
print(destination.hunger) -- prints 8
print(destination.armor) -- prints 3
print(destination.name) -- prints Steve

YAY! Now you can store variables in a file.

NOTE: You cannot store functions or "threads" (ok, coroutines) in files, because textutils doesn't like them. Of course, you could store a function dump, but I'm not sure what would happen to textutils then.

LBPHacker, on 22 February 2013 - 06:49 PM said:

NOTE: You cannot store variables or "threads" (ok, coroutines) in files, because textutils doesn't like them. Of course, you could store a function dump, but I'm not sure what would happen to textutils then.

To be more specific, textutils doesn't like anything isn't a number, boolean, string, or table (so long as the table is without recursive entries). You can store variables in the serialized table so long as they are one of those types.

dexterden, on 23 February 2013 - 12:38 AM said:

The variables can be stored in files so long as they are of the same type.

Not true. They can be different types

-- our variables of different data types
local num = 5
local str = "Hi from string!"
local t = { "table", "data", 4 }
local bool = true

-- writing the above variables to the same file
local handle = fs.open("someFile", "w")
handle.write(tostring(num).."\n")
handle.write(str.."\n")
handle.write(textutils.serialize(t).."\n")
handle.write(tostring(bool).."\n")
handle.close()

-- reading those variables from the file
local handle = fs.open("someFile", "r")
num = tonumber( handle.readLine() )
str = handle.readLine()
t = textutils.unserialize( handle.readLine() )
bool = ( handle.readLine() == "true" )
handle.close()

Oh crap, not

LBPHacker, on 22 February 2013 - 06:49 PM said:

variables or "threads"

but FUNCTIONS and THREADS. Sorry…

EDIT: fixed