In addition to your stuff:

• Always provide necessary variables that may be interesting in the context of the error.
  

  die("Could not open file $file: $!\n");
  [download]

• Always put delimiters around the variables, so that you don't get tricked by whitespace, weird chars, line feeds, etc.
  

  die("Could not open file ($file): ($!)\n");
  [download]

/J