#not using strict and -w for this example only
my $rd = int( rand(100000)) + 999999;

my @files = qw( XYZ12345_X05_20110805_8999999_00001.TXT XYZ12345_X05_20110805_9999999.TXT);

#add dash between $3 and $4 to the .txt before processing them:::
#pad $2 with 0s

#replace the end of the file with a randon number if the filename ends with _00001
foreach my $f(@files) {
    
  if($f=~/(^\w{3})(\d{5,7})(_\w{1})(\w{1,2}_)(\d{8}\_)(\d{7}_\d{5}\.\w{3})/i) {

    (my $xrenamed = $f) =~s/(^\w{3})(\d{5,7})(_\w{1})(\w{1,2}_)(\d{8}\_)(\d{7}_\d{5}\.\w{3})/$1.sprintf("%07d",$2).$3."-".$4.$5.$rd.".txt"/ie;
     print "\n\n $xrenamed\n\n";

  }else{
      
      (my $xrenamed = $f) =~s/(^\w{3})(\d{5,7})(_\w{1})(\w{1,2}_)(\d{8}\_)(\d{7}_\.\w{3})/$1.sprintf("%07d",$2).$3."-".$4.$5.$6/ie;
      print "\n\n $xrenamed\n\n";

    }
}