Here's a very straight-forward way to do this:

my $digit_count = ($input =~ tr/[0-9]//);
my $white_count;
while ($input =~ m/\s/g) { $white_count++; } # note: can't use tr/\s//
my $word_count;
while ($input =~ m/\w+/g) { $word_count++; }
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As is generally the case with perl, there are many ways to perform these tasks.