Is there a Perl shortcut to count the number of matches in a string?

Question

Suppose I have:

my $string = \"one.two.three.four\";

How should I play with context to get the number of times the pattern found a match (3

Answer 1

I noticed that if you have an OR condition in your regular expression (eg /(K..K)|(V.AK)/gi ) then the array produced may have undefined elements which are included in the count at the end.

For example:

my $seq = "TSYCSKSNKRCRRKYGDDDDWWRSQYTTYCSCYTGKSGKTKGGDSCDAYYEAYGKSGKTKGGRNNR";
my $regex = '(K..K)|(V.AK)';
my $count = () = $seq =~ /$regex/gi;
print "$count\n";

Gives a value of count of 6.

I found the solution in this post How do I remove all undefs from array?

my $seq = "TSYCSKSNKRCRRKYGDDDDWWRSQYTTYCSCYTGKSGKTKGGDSCDAYYEAYGKSGKTKGGRNNR";
my $regex = '(K..K)|(V.AK)';
my @count = $seq =~ /$regex/gi;
@count = grep defined, @count; 
my $count = scalar @count;
print "$count\n";

Which then gives the correct answer of three.