... I'm trying to count digits in a scalar
That's what the OP says, but the /\d\D*/g regex suggests misterperl is trying to count occurrences of some kind of digit-group pattern. If that's the case, I can, offhand, think of some s/// approaches (in the vein of a tr/// operation) that would do the trick as well as the m// approach that misterperl seems to favor:
c:\@Work\Perl\monks>perl -wMstrict -le
"$_ = '+++1223w3433.45+34***';
;;
my $ndg;
;;
$ndg =()= /\d\D*/g;
print qq{A: $ndg digit grps.; m// change unpossible '$_'};
;;
$ndg = do { (my $r = $_) =~ s/\d\D*//g };
print qq{B: $ndg digit grps.; s/// string unchanged '$_'};
;;
$ndg = s/(\d\D*)/$1/g;
print qq{C: $ndg digit grps.; s/// string unchanged '$_'};
;;
$ndg = s/\d\D*//g;
print qq{D: $ndg digit grps.; s/// string CHANGED '$_'};
"
A: 12 digit grps.; m// change unpossible '+++1223w3433.45+34***'
B: 12 digit grps.; s/// string unchanged '+++1223w3433.45+34***'
C: 12 digit grps.; s/// string unchanged '+++1223w3433.45+34***'
D: 12 digit grps.; s/// string CHANGED '+++'
My own preference would be for the m// approach.
Give a man a fish: <%-{-{-{-<
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