local fileInput = { }

local file, err = io.open ( "path/to/my/file.txt", "r" )
if not file then error ( err ) end
for line in file:lines ( ) do
  fileInput[ #fileInput + 1 ] = line
end

doThingsWith ( fileInput )

scriptResults = runMyScript ( )

local file, err = io.open ( "path/to/my/file.txt", "w" )
if not file then error ( err ) end
file:write ( type ( scriptResults ) == "table" and table.concat ( scriptResults , "\n" ) or scriptResults )
file:close ( ) 

local fileInput = { }

local file, err = io.open ( "path/to/my/file.txt", "r" )
if not file then error ( err ) end
for line in file:lines ( ) do
  fileInput = line
end

doThingsWith ( fileInput )