I'll add my two cents on top of what others have posted...

Firstly I would NOT use autodie until you've learned how to deal with files without it.

It's a shortcut for people that know what they are doing (and you're not quite there yet).

Then ALWAYS use strict;. ALWAYS. Absolutely ALWAYS.

The normal idiom for opening filehandles is this:

open my $fh, "<", "blah.txt" or die $!;
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This declares a lexical file-handle and opens it, dying if there is an error.

Feel free to modify it, once you understand what it does.