print IsNumber("0777 891 777") . "\n"; # 0
print IsNumber("1.5671") . "\n"; # 1
print IsNumber("121A3D") . "\n"; # 0
print IsNumber("777") . "\n"; # 1
print IsNumber("0") . "\n"; # 1
print IsNumber("-4.567") . "\n"; # 1
print IsNumber("+9.8.97") . "\n"; # 0
print IsNumber("+9.897") . "\n"; # 1
print IsNumber("+9.8¬97") . "\n"; # 0
print IsNumber("9.8[97") . "\n"; # 0


sub IsNumber
{
   my ($string) = @_;
   my $valid = 0;
   my $count = $string =~ tr/\.//;

   if ( $string =~ m/[a-zA-Z\ \[\]]/ )
   {
      $valid = 0;
   }
   elsif ( $string =~ /[^\x00-\x7F]/ )
   {
      $valid = 0;
   }
   elsif ( $count > 1 )
   {
      $valid = 0;
   }
   elsif ( $string =~ m/[#@':;><,.{}[]=!"£$%^&*()]/ )
   {
      $valid = 0;
   }
   elsif ( $string =~ m/^[+-]?\d+$/ )
   {
      $valid = 1;
   }
   elsif ( $string =~ m/^[+-]?[0-9]+[.]?[0-9]+/ )
   {
      $valid = 1;
   }

   return $valid;
}