Localizing $@ would have protected your caller against your clobbering $@. You'd still have the alias/copy bug so now shift() would always return undef because $@ now is always blank but at least you'd be safer. When using $@, always, always, always copy it out first. The smallest piece of code can go clobber $@ so you should always copy it out before examining it.

sub foo {
    local $@;
    return eval { bar( shift ) } || 0;
}
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