Some suggestions:

• You can use different delimiters in s///, so

  $sourceDir =~ s/\/\$/\$/;
  
  # is better written as
  $sourceDir =~ s#/\$#$#;
  [download]

  btw, what is that supposed to do? It replaces a '/$' with a '$' sign, I see no obvious use for that ...
• Instead of comparing files with a call to the external command diff - use File::Compare - it's portable and doesn't spawn an external process.

-- Hofmator