Ah, well the last time I used this construct it was for a function that could accept either a unix timestamp as a scalar, or a time vector as returned by localtime() or gmtime().

So I was checking the length of @_ to see if it was greater than 1 (not 0), like this:

sub unix_to_datetime {
  my @time_vec;
  @time_vec = @_ if @_>1;
  unless (@time_vec) {
    my $time = shift;
    @time_vec = (defined $time ? localtime($time) : localtime);
  }
  return strftime('%Y-%m-%d %H:%M:%S', @time_vec);
}
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