According to the documentation for Storable:

    Storable uses the "exception" paradigm, in that it does
    not try to workaround failures: if something bad happens,
    an exception is generated from the caller's perspective
    (see Carp and croak()).  Use eval {} to trap those
    exceptions.
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So, your code might look something like this:

$existref = eval { retrieve($filename) };

if (not $existref) {
  nice_error_message("Error retrieving data: $@");
}
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