When you include the use utf8 pragma, all this says to Perl is that your script itself is written in UTF-8. It says nothing about what encoding it used by different filehandles.

Regardless of your environment, handles in Perl default to operating as binary byte streams. (The exact details depend on whether you're on an MS-DOS-like machine or a Unix-like machine, but the results are much the same.) This is documented in PerlIO.

Once upon a time (in Perl 5.8.0), Perl used to automatically pick up the locale from the environment. This was somewhat unpredictable and unexpected, and this feature was removed in the next Perl release (5.8.1).

Now, if you want Perl to sniff your environment you need to explicitly ask for it. With binmode or the open pragma, use the :locale layer.

You might also want to check out the -C command line option which provides some facilities for switching the standard input/output/error handles to UTF-8, either unconditionally or depending on your environment.