Create a new version of paste:

-- Extensions version 2.1 by KnightMiner

-- Check if we are loading as an API or running the startup
if not shell then
  -- Load the list of extensions
  local file = fs.open( "extensions.cfg", "r" )
  list = textutils.unserialize( file.readAll() )
  file.close()
  
  -- Function to check if a program is a file and what to run it with
  function program( name )
    local prog, file, noExt
    if name:find( '^".-"' ) then
      prog = list[string.match( name, '^".-%.([^. ]+)"' )]
      file = string.match( name, '^(".-%.[^. ]+")' )
      noExt = name:gsub( '^"(.-)%.[^. ]+"', '"%1"' )
    else
      prog = list[string.match( name, '^[^ ]-%.([^. ]+)' )]
      file = string.match( name, '^([^ ]-%.[^. ]+)' )
      noExt = name:gsub( '^([^ ]-)%.[^. ]+', '%1' )
    end
    if type( prog ) == "table" then
      if prog.noExt then
        return prog[1], file, noExt
      else
        return prog[1], file
      end
    else
      return prog, file
    end
  end
  
-- Running as a program
else
  -- validate args
  local args = { ... }
  if #args > 2 or args[1] == "usage" then
    print( "Usage: extensions [option] [option2]" )
  end

  -- Check for an extensions configuration file
  -- If it does not exist, ask to create it
  if not fs.exists( "extensions.cfg" ) then
    function create( default )
      print( "Creating extension.cfg" )
      local file = fs.open( "extensions.cfg", "w" )
      file.write( '{\n  -- Lua table containing file extensions\n  cfg = "edit"\n}' )
      file.close()
      if default then
        print( "Created default extensions.cfg" )
      else
        shell.run( "edit extensions.cfg" )
      end
    end
    if args[1] == "create" or args[1] == "create-default" then
      create( args[1] == "create-default" )
    elseif args[1] == "skip" then
      print( "Missing extensions.cfg file, cancelling" )
      return
    else
      print( "Missing extensions.cfg file, create it? (y/n)" )
      while true do
        local _, key = os.pullEvent( "key" )
        -- remove any stray character events
        os.startTimer(0.1)
        os.pullEvent()
        if key == keys.y then
          create()
          break
        elseif key == keys.n then
          print( "Cancelling extension loading" )
          return
        end
      end
    end
  end

  -- Check to see if we already ran the extension program
  -- And if so, ask if we should reload
  if extensions then
    if ( args[2] or args[1] ) == "load" then
      print( "Extensions already loaded, cancelling" )
      return
    elseif ( args[2] or args[1] ) == "reload" then
      print( "Reloading extension support" )
    else
      print( "Extensions already loaded, reload them? (y/n)" )
      while true do
        local _, key = os.pullEvent( "key" )
        -- remove any stray character events
        os.startTimer(0.1)
        os.pullEvent()
        if key == keys.y then
          print( "Reloading extension support" )
          break
        elseif key == keys.n then
          print( "Cancelling extension reloading" )
          return
        end
      end
    end
    os.unloadAPI( "extensions" )
  else
    -- Preserve the original method of running
    print( "Loading extension support" )
    shell.runRaw = shell.run
  end

  os.loadAPI( "extensions" )
  if not extensions.list then
    print( "Error loading extensions" )
    return
  end

  -- Override the shell.run function, so extensions run is used by default
  shell.run = function( name, ... )
    local program, progName, noExt = extensions.program( name )
    if program then
      if fs.exists( progName ) then
        return shell.runRaw( program, noExt or name, ... )
      else
        printError( "No such file" )
        return false
      end
    else
      return shell.runRaw( name, ... )
    end
  end

  print( "Extensions successfully loaded" )
end