content = "Now is the time"

lp =
  # user pattern machting to open file and assign it to variable
  with {:ok, file} = File.open("/etc/passwd"),
       content = IO.read(file, :all),
       :ok = File.close(file),
       # use regex to find uid and guid. MatchError, if there's no such user.
       [_, uid, gid] = Regex.run(~r/^root:.*?:(\d+):(\d+)/m, content) do
    "Group: #{gid}, User: #{uid}"
  end
# => Group: 26, User: 26
IO.puts(lp)
# => Now is the time
IO.puts(content)