Basic

_G
Description: Global variable that holds the global environment (all global functions/variables)
Example:
print(_G.tostring(true)) -- tostring is global, which makes it accessible via _G as well
setfenv
Description: sets the environment for a function to use, rather than _G.
Usage: setfenv(f)
Example:
function x()
    zzz.x = 5
    print() -- will not work here, the environment is not _G.
end
​
setfenv(x, {zzz = {x = 10}})
getfenv
Description: returns the environment in use by given function or stack level, default 1.
Usage: getfenv([f])
Example:
function x()
    zzz.x = 5
    print() -- will not work here, the environment is not _G.
end
​
setfenv(x, {zzz = {x = 10}})
print(getfenv(x)) -- environment is {zzz = {x = 10}}
setmetatable
Description: sets the metatable for given table
Usage: setmetatable(table, metatable)
Example:
local t = {}
setmetatable(t, {__call = print})
getmetatable
Description: gets the metatable of specified table, returning the __metatable metamethod's value if applicable
Usage: getmetatable(table)
Example:
local t = {}
setmetatable(t, {__call = print})
print(getmetatable(t)) -- {__call = print}
setmetatable(t, {__metatable = {x = 5}})
print(getmetatable(t)) -- {x = 5}
rawset
Description: sets a value in the table at specified index without invoking any metamethods
Usage: rawset(table, index, value)
Example:
local t = {}
setmetatable(t, {__newindex = function(self, k, v)
    print('Value set at index '.. tostring(k) ..' to value '.. tostring(v))
end})
​
t.x = 5 -- Value set at index x to value 5
rawset(t, 'xx', 50) -- prints nothing, __newindex is not be invoked
rawget
Description: returns a value from a table at given index without invoking any metamethods
Usage: rawget(table, index)
Example:
local t = {}
setmetatable(t, {__index = function(self, k, v)
    print('Accessing value at index '.. tostring(k))
end})
​
print(t.x) -- Accessing value at index x
print(rawget(t, 'x')) -- nothing, __index is not invoked
rawequal
Description: compares two values using == without invoking any metamethod
Usage: rawequal(v1, v2)
Example:
local mt = {__eq = function(a, b)
    print('Checking equality ( '.. tostring(a) ..' vs '.. tostring(b) ..' )')
    return rawequal(a, b)
end}
​
local t = {}
setmetatable(t, mt)
​
local t2 = {}
setmetatable(t2, mt)
​
print(t == t2) -- Checking equality ( table: 00f28b00 vs table: 00f28a10 )
print(rawequal(t, t2)) -- nothing, __eq is not invoked
pairs
Description: iterator to traverse over a table in any order possible
Usage: pairs(t)
Example:
local t = {1, 2, 3}
for k, v in pairs(t) do
    print(k, v)
end
ipairs
Description: iterator to traverse over a table in sequence
Usage: ipairs(t)
Example:
local t = {1, 2, 3}
for k, v in ipairs(t) do
    print(k, v)
end
loadstring
Description: loads a Lua chunk
Usage: loadstring(string [, chunkName])
Example:
local f = loadstring([[return function() print(123) end]])
f() -- 123
loadfile
Description: loads a Lua chunk from specified file, or from standard input if filename is not specified
Usage: loadfile([filename])
Example:
-- x.lua
return function() print(123) end
​
-- other file.lua
local f = loadfile("x.lua")
f() -- 123
next
Description: returns the next key, value pair in table starting from specified index, otherwise index, is nil
Usage: next(table [, index])
Example:
local t = {1, 2, 3}
print(next(t, 2)) -- 3, 3
print(next(t)) -- 1, 1
pcall
Description: calls a function in a protected state, returning any errors if they happen, otherwise returns true if successful plus the returned values from f
Usage: pcall(f, ...)
Example:
function x(n)
    return x + n
end
​
local success, ret = pcall(x, 5)
print(success, ret) -- false    C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')
xpcall
Description: calls a function in a protected state, using err as the error handler and returning true if no errors happen, otherwise returns false plus the result from err
Usage: xpcall(f, err)
Example:
function x(n)
    return x + n
end
​
local function x_error_handler(error)
	print(error)
	return 123
end
​
local success, ret = xpcall(x, x_error_handler)
print(success, ret)
Output:
C:\Users\user\lua_file.lua:2: attempt to perform arithmetic on a function value (global 'x')
false 123
unpack
Description: unpacks a table in sequence, starting from i and ending with j (1, #table respectively by default), returning all values from it
Usage: unpack(table [, i [, j]])
Example:
local t = {1, 2, 3, 4, 5}
print(unpack(t)) -- 1, 2, 3, 4, 5
print(unpack(t, 2, 4)) -- 2, 3, 4
type
Description: returns the data type of given value
Usage: type(value)
Example:
print(type(123)) -- number
print(type({})) -- table
print(type(nil)) -- nil
print(type('')) -- string
print(type(true)) -- boolean
tonumber
Description: converts value to a number if possible
Usage: tonumber(val [,base])
Example:
local x = '5'
print(tonumber(x)) -- 5
print(type(tonumber(x))) -- number
print(type(x)) -- string
tostring
Description: converts value to a string
Usage: tostring(val)
Example:
print(tostring({})) -- table: 00ee88a8
print(tostring(5)) -- 5
​
print('This is a boolean: '.. tostring(true)) -- This is a boolean: true
​
​