There are quite a ways to drop the -ve sign...

my $due = -9.98;

printf "substr_idx: %s\nneg_one_mul: %s\nregex: %s\n"
  , substr_idx($due)
  , neg_one_mul($due)
  , regex($due);

sub substr_idx
{ my $number = shift;
  return
    -1 < index($number , '-' , 0)
    ? substr($number , 1)
    : $number;
}

sub neg_one_mul
{ my $number = shift;
  return
    $number =~ m/^-/
    ? $number * -1
    : $number;
}

sub regex
{ my $number = shift;
  return
    $number =~ m/^- (.+)/x
    ? $1
    : $number;
}
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...Whatever you do just do not try to compare a floating point number (-9.98) against an integer (0) (or another float) -- due to inherent error in number representation -- w/o using some minimum difference that you would treat to be same as zero.