use Date::Calc qw(Today Days_in_Month);
     my ($year, $month, $day) = Today();
     return Days_in_Month($year,$month - 1);
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That's not going to work in January. You should also import the Add_Delta_YMD function:

sub dayslastmonth
{
  use Date::Calc qw(Today Days_in_Month Add_Delta_YMD);
  my ($year,$month,$day) = Add_Delta_YMD(Today(), 0, -1, 0);
  return Days_in_Month($year,$month);
}
[download]

buckaduck