Not quite sure exactly what you are looking for, but something like this might serve:

>perl -wMstrict -le
"my $x = '\\files\builds\data\M9998SBQCACSYD30401S';
 ;;
 if ($x =~ m{ (Y [[:alpha:]] \d) }xms) {
   print qq{match: '$1'};
   }
"
match: 'YD3'
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