use strict;
use warnings;

sub fmthd { # number, decimal separator, thousands separator
  my ( $dec, $thd ) = ( $_[1] // ".", $_[2] // "," );
  my ( $n, $d ) = split /\Q$dec\E/, shift;
  my $s = $n<0?"-":"";
  $n = reverse $n;
  return $s.reverse( $n = join $thd, $n =~ /(\d{1,3})/g ).($d?"$dec$d":"${dec}00");
}

print fmthd( 1234567.14 ), "\n";
print fmthd( 1234567 ), "\n";
print fmthd( 12.14 ), "\n";
print fmthd( 123456.14343 ), "\n";
print fmthd( 1234567.14 ), "\n";
print fmthd( 8881234567.14 ), "\n";
print fmthd( -8881234567.14 ), "\n";
print fmthd( "-8881234567,14", ",", "." ), "\n";