In Perl, you can count the number of elements in an array that matches a certain condition by using the grep function and then taking the size of the resulting array.
Here's an example: let's say you have an array @nums containing some integers and you want to count the number of elements in the array that are greater than 10. You can use the following code:
my @nums = (5, 10, 15, 20, 25);
my @matching_nums = grep { $_ > 10 } @nums;
my $count = scalar @matching_nums;
print "There are $count numbers greater than 10 in the array.\n";
This code first uses grep to create a new array @matching_nums containing only the elements of @nums that are greater than 10. The $_ variable represents the current element being processed in the loop. The scalar function is then used to get the size of the resulting array, which is stored in the $count variable. Finally, the script prints a message indicating the number of elements found.
The output of this script would be:
There are 3 numbers greater than 10 in the array.