DB<5> $str =  '123X12'                                                        

  DB<6> p $str                                                                  
123X12
  DB<7> if ( $str =~ /^(\d{2,4})[^\d](\d{2})/) { print "$1;$2" }                
123;12
  DB<8> $str =  '123{12'                                                        

  DB<9> if ( $str =~ /^(\d{2,4})[^\d](\d{2})/) { print "$1;$2" }                
123;12