a) The encoding of the script is not relevant to the encoding of the data manipulated by the process as long as you indicate to perl what the script encoding is if you use non-ascii literals in it. See: encoding

b) Don't worry about (or rely on an assumption about) what internal coding perl uses. http://http://perldoc.perl.org/perlunifaq.html#I-lost-track%3B-what-encoding-is-the-internal-format-really%3F

c) If you know what the encoding of the data you are reading is, use decode() on it, or binmode(:encoding(xxx)) on the filehandle. This will convert it into the internal encoding so you can do what have you, such as encode() it into some different encoding.

binmode Encode

d) If you don't know what the encoding of read data is, that's problematic. There isn't a definitive way to sort them out.