Convert SteamID to CommunityID. Shamelessly cobbled together from various pieces on the internet.

steamid.lua

local STEAMID = arg[1]

-- Generic split function found on the internet
-- http://coronalabs.com/blog/2013/04/16/lua-string-magic/
function string:split( inSplitPattern, outResults )
   if not outResults then
      outResults = { }
   end
   local theStart = 1
   local theSplitStart, theSplitEnd = string.find( self, inSplitPattern, theStart )
   while theSplitStart do
      table.insert( outResults, string.sub( self, theStart, theSplitStart-1 ) )
      theStart = theSplitEnd + 1
      theSplitStart, theSplitEnd = string.find( self, inSplitPattern, theStart )
   end
   table.insert( outResults, string.sub( self, theStart ) )
   return outResults
end

-- Convert SteamID to Community ID (64)
function SteamIdToCommunityId( sid )
	local id = sid:split( ":" ) id = ( ( ( id[3] * 2 ) + id[2] ) + 1197960265728 ) id = "7656" .. id 
	return id
end

print( SteamIdToCommunityId( STEAMID ) )