In Perl, how to count the number of occurences of successful matches based on a condition on their absolute positions

Question

Using just one Perl substitute or matching regular expression statement , how can we modify below code:

I need to modify the value of $pattern<

Answer 1

You can use the perl special variable @LAST_MATCH_START to get the output:

use strict;
use warnings;

my $pattern = "F1";  
my $string  = "F1234F12F1F1234F12F13";     
my $count;      
while ( $string =~ /$pattern/g ) {
    $count++ if $-[0] % 5 == 0;
} 
print $count;

Output:

4