Updated for OS(edited)

-- This is edited version of eniallator's updater program for Marlins OS, edited by Marlin.
-- The way it works is it will compare a version variable in 2 files; 1 pastebin link and 1 local file.
-- NOTE: it does not compare the contents of the file, it only compares a variable.
-- ================================================================================
--
-- To make a version variable in your file copy and paste the following into the file:
--
-- version = "*insert version here*"
--
-- This has to be in the local file aswell as the pastebin file to download.
-- ================================================================================
--
-- To add your file to be updated when running this program add the following to the filesToUpdate table:
--
-- *insert file name* = "*insert pastebin code after 'http://pastebin.com/'*"
--
-- The file name must correspond to your local file on your computercraft computer and the pastebin link has to correspond to your file in pastebin.

local filesToUpdate = {"os/os_Programs/os_MainScript" = "8zek1eez"}
-- Table for files/pastebin codes

function getFile(fileName, link)

  local file = http.get("http://pastebin.com/raw.php?i=" .. textutils.urlEncode(link))

  if file then

     local out = file.readAll()
     file.close()
     return out
     -- Returning contents of the pastebin file
  else

     return false
     -- Returning false if the link is invalid
  end
end
-- Function for downloading the files from pastebin, needs HTTP to run

function getVersion(fileContents)

  if fileContents then
    local _, numberChars = fileContents:lower():find('version = "')
    local fileVersion = ""
    local char = ""
    -- Declaring variables aswell as finding where in the fileContents argument is 'version = "'

    if numberChars then
      while char ~= '"' do

        numberChars = numberChars + 1
        char = fileContents:sub(numberChars,numberChars)
        fileVersion = fileVersion .. char
      end
      -- Making the version variable by putting every character from 'version = "' to '"'

      fileVersion = fileVersion:sub(1,#fileVersion-1)
      return fileVersion
    else

      return false
      -- If the function didn't find 'version = "' in the fileContents then it returns false
    end
  else

    return ""
  end
end
-- Finding the version number

for file, url in pairs(filesToUpdate) do

  if not fs.isDir(file) then

    local pastebinContents = getFile(file,url)
    -- Getting the pastebin file's contents

    if pastebinContents then
      if fs.exists(file) then

        local localFile = fs.open(file,"r")
        localContents = localFile.readAll()
        localFile.close()
        -- Getting the local file's contents
      end

      local pastebinVersion = getVersion(pastebinContents)
      local localVersion = getVersion(localContents)
      -- Defining version variables for each of the file's contents

      if not pastebinVersion then

        print("[Error  ] the pastebin code for " .. file .. " does not have a version variable")
        -- Tests if the pastebin code's contents has a version variable or not

      elseif not localVersion then

        print("[Error  ] " .. file .. " does not have a version variable")
        -- Tests if the local file doesn't have the version variable

      elseif pastebinVersion == localVersion then

        print("[Success] " .. file .. " is already the latest version")
        -- If the pastebin file's version is equal to the local file's version then it does nothing
      else

        endFile = fs.open(file,"w")
        endFile.write(pastebinContents)
        endFile.close()

        print("[Success] " .. file .. " has been updated to version " .. pastebinVersion)
        -- If the versions are not the same then it will write over the current local file to update it to the pastebin version
      end
    else

      print("[Error  ] " .. file .. " has an invalid link")
     end
  else

    print("[Error  ] " .. file .. " is a directory")
  end
end
-- Error messages catching different errors