Rethrowing an exception with die $@ if (some expression involving $@) (an idiom mentioned at least 6 times in the perl documentation) has a problem when the expression involving $@ ends up doing anything that inadvertently clears $@. Consider: 
use overload q!""!=>sub{ eval { "whoops" } };
eval { die bless {} };
die $@ if $@;

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Here, we die with an exception object that should stringify to "whoops", but $@ ends up being cleared before the rethrow. (To highlight the maybe-expected vs. observed results, change eval { "whoops" } to just "whoops" or remove the if $@.) The better way to do it would be 
use overload q!""!=>sub{ eval { "whoops" } };
eval { die bless {} };
my $exception = $@;
die $exception if $exception;

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In reply to Rethrowing with die $@ considered harmful by ysth

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