SimplestBootloader

if _G.bootloaded == true then return end -- ensures that startup runs only once
--------------------------------------------------------------------------------
--- Simplest Bootloader for ComputerCraft 1.6
-- @version 0.4-beta
-- @author  Shefla
-- @license MIT
-- @changelog
--    0.1 Initial version adapted from Geforce Fan's TLCO concept
--    0.2 Added rednet.run spoofing to avoid forced autostart
--        Switched from terminate event to modem_message to trigger printError
--    0.3 Public release, added comments to config section
--    0.4 Removed hardcoded CraftOS version from default config (use os.version)
--------------------------------------------------------------------------------

-- Title of the bootloader screen
local title  = 'Simplest Bootloader v0.4-beta'

-- Bootable entries configuration
-- If there is only one entry it is booted without displaying menu
local entries = {
    {
        -- name is used when displaying menu
        name = os.version()
        -- boot function executed on selection (shell API not available)
    , boot = function ()
            -- from bios.lua
            parallel.waitForAny(
                function ()
                    os.run({}, term.isColor()
                        and '/rom/programs/advanced/multishell'
                        or  '/rom/programs/shell'
                    )
                end
            , function () rednet.run() end
            )
        end
    }
, {
        name = os.version()..' (no rednet, no multishell)'
    , boot = function ()
            term.redirect(term.native())
            os.run({ multishell = false }, '/rom/programs/shell')
        end
    }
}

--8<-- Probably no need to edit below --8<--------------------------------------
local nativePrintError = _G.printError
local nativeRednetRun  = _G.rednet.run
function _G.rednet.run () error('', 0) end
function _G.printError ()
    local entry
    _G.bootloaded = true
    _G.printError = nativePrintError
    _G.rednet.run = nativeRednetRun
    if #entries == 1 then entry = entries[1]
    else
        term.clear()
        term.setCursorPos(1, 1)
        print(title)
        print()
        for index, entry in pairs(entries) do
            print('F'..index..': '..entry.name)
        end
        while true do
            local event, key = os.pullEvent('key')
            local index = key - 58
            if entries[index] ~= nil then
                entry = entries[index]
                break
            end
        end
    end
    print('Launching '..entry.name)
    local ok, err = pcall(entry.boot)
    if not ok then
        printError(err)
        print('Press any key to continue')
        os.pullEvent('key')
    end
    os.shutdown()
end
os.queueEvent('modem_message')