open my $fh, ">", "important-file" or die;
[download]

Very costly if the > was a mistyped <.

IMO, the warnings pragma is the wrong type of tool for detecting typos like the OP made. After all, such a check only needs to be done once (or once after each change). There's absolutely no point in paying the penalty for each and every run. Check like this (if once could actually make a check that doesn't trigger too many false positives) belong in a linter. Perl::Critic is a well used linter in the Perl world. And of course one has their test suite, which should be able to catch mistakes like that.