Sometimes it's best to start simple with these things. Here's an alternate approach that seems to do what you seem to want done:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my @test = qw(RC1XY  RS);
 ;;
 for my $s (@test) {
   printf qq{'$s' -> };
   my ($p_r, $d1, $p_mc, $p_new_mc) = $s =~ m{
     ([[:upper:]]+) (?: (\d+) ([[:upper:]]) ([[:upper:]]))?
     }xms;
   dd $p_r, $d1, $p_mc, $p_new_mc;
   }
"
'RC1XY' -> ("RC", 1, "X", "Y")

'RS' -> ("RS", undef, undef, undef)
[download]

Update: I notice you write that you want a "blank" (which I take to be an empty string) to be produced for sub-patterns that do not match. You will note that the example above yields undefined values for non-matching sub-patterns. Since the empty string and undef both have a false boolean value, I find it is usually just as easy to test and deal with undefs as with empty strings and so I usually avoid the extra effort to produce an empty string. If you really need them, here's a possible alternative approach:

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le
"my @test = qw(RC1XY  RS);
 ;;
 for my $s (@test) {
   printf qq{'$s' -> };
   my ($p_r, $d1, $p_mc, $p_new_mc) = $s =~ m{
     ([[:upper:]]+) (\d*) ([[:upper:]]?) ([[:upper:]]?)
     }xms;
   dd $p_r, $d1, $p_mc, $p_new_mc;
   }
"
'RC1XY' -> ("RC", 1, "X", "Y")

'RS' -> ("RS", "", "", "")
[download]

Thanks for approach and I really appreciate your help on this

Although you showed me the result what I wanted but I needed something more

I guess I gave you simple example to illustrate the problem I faced. In my earlier example I used the regular expression as '(.*) (0-9) (A-Z) ((A-Z)'

I ran the code snippet you gave me for 'RW12QW1XY' and it does not work and where as expected out come is as below

'RW12QW1X' -> ("RW12QW", "1", "X", "")

Please post your test code and output in something like the format shown below, and please use code tags; I can't really understand your regex without guessing! Please also give your expected/desired output; "it does not work" does not tell me very much.

c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -e
"my @test = qw(RC1XY RS RW12QW1X FOO FOOx FOO23PQ xFOO23PQXXX foo xyzz
+y);
 ;;
 for my $s (@test) {
   printf qq{'$s' -> };
   if (my ($p_r, $d1, $p_mc, $p_new_mc) = $s =~ m{
     ([[:upper:]]+) (\d*) ([[:upper:]]?) ([[:upper:]]?)
     }xms) {
     dd $p_r, $d1, $p_mc, $p_new_mc;
     }
   else {
     print qq{no match \n};
     }
   }
"
'RC1XY' -> ("RC", 1, "X", "Y")
'RS' -> ("RS", "", "", "")
'RW12QW1X' -> ("RW", 12, "Q", "W")
'FOO' -> ("FOO", "", "", "")
'FOOx' -> ("FOO", "", "", "")
'FOO23PQ' -> ("FOO", 23, "P", "Q")
'xFOO23PQXXX' -> ("FOO", 23, "P", "Q")
'foo' -> no match
'xyzzy' -> no match
[download]

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Give a man a fish:   <%-(-(-(-<

You are not giving us enough information to work with. Please provide a large enough set of example inputs with their expected outputs to cover the expected combinations of actual input.

Here are more example strings :

1. Sample1Repeat1A -> ("Sample1Repeat", "1", "A", "")

2, Sample2Repeat2 -> ("Sample2Repeat", "2", "", "")

3. Sample3Repeat -> ("Sample3Repeat", "", "", "")

4. 4SampleRepeat -> ("4SampleRepeat", "", "", "")

5. 4SampleRepeat4 -> ("4SampleRepeat", "4", "", "")

6. 5SampleRepeat5D -> ("4SampleRepeat", "5", "D", "")

I hope these samples help giving more information.

Here are more example strings :

1. Sample1Repeat1A -> ("Sample1Repeat", "1", "A", "")

2, Sample2Repeat2 -> ("Sample2Repeat", "2", "", "")

3. Sample3Repeat -> ("Sample3Repeat", "", "", "")

4. 4SampleRepeat -> ("4SampleRepeat", "", "", "")

5. 4SampleRepeat4 -> ("4SampleRepeat", "4", "", "")

6. 5SampleRepeat5D -> ("4SampleRepeat", "5", "D", "")

I hope these samples help giving more information.

I still don't understand if these are examples of what you are getting from a regex that "doesn't work" or examples of what you want to extract from the given strings. In any event, here's an approach that produces the given output. I don't say it's the most efficient or elegant.

c:\@Work\Perl\monks>perl -wMstrict -e
"my @test = qw(
   Sample1Repeat1A Sample2Repeat2 Sample3Repeat 4SampleRepeat
   4SampleRepeat4  5SampleRepeat5D
   );
 ;;
 for my $s (@test) {
   printf qq{'$s' -> };
   if (my ($p_r, $d1, $p_mc, $p_new_mc) = $s =~ m{
     \b (.+?) (?: (\d*) (?: ([[:upper:]]?) ([[:upper:]]?) )? )? \b
     }xms) {
     printf qq{'$_' } for $p_r, $d1, $p_mc, $p_new_mc;
     print qq{\n};
     }
   else {
     print qq{no match \n};
     }
   }
"
'Sample1Repeat1A' -> 'Sample1Repeat' '1' 'A' ''
'Sample2Repeat2' -> 'Sample2Repeat' '2' '' ''
'Sample3Repeat' -> 'Sample3Repeat' '' '' ''
'4SampleRepeat' -> '4SampleRepeat' '' '' ''
'4SampleRepeat4' -> '4SampleRepeat' '4' '' ''
'5SampleRepeat5D' -> '5SampleRepeat' '5' 'D' ''
[download]

(I just love playing regex Whack-A-Mole!)

Update: sjain: I just saw your note above about not having access to Data::Dump, so I've changed the example code to a version that uses neither that module nor Data::Dumper, the output of which doesn't look so good in this instance.

Further Update: I tried this regex with strings  RS RC1XY RW12QW1X and while the latter two parse ok,  RS does not, so AnonyMonk's approach below looks like a better one.

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Give a man a fish:   <%-(-(-(-<