Re^4: A regex that only matches at offset that are multiples of a given N? (Update:almost perfect!)

in reply to Re^3: A regex that only matches at offset that are multiples of a given N? (Update:almost perfect!)
in thread A regex that only matches at offset that are multiples of a given N?

That's a possible approach that is effectively similar to simply ignoring non-aligned matched (the next if pos() % 4; stuff above), but the real saving would only be achieved by only calling out from the regex engine for aligned matches.

It seems like it ought to be possible to reposition the \G somewhere after the (?:.{$n}) to avoid the duplicates. But I've tried various places including:

#! perl -slw
use strict;

my $s = join '', map {
    ('a'..'z')[ rand 26 ]
} 1 .. 1000;

our $N //= 4;

for my $key ( 'aa' .. 'zz' ) {
    print "$-[1] : $1"
        while $s =~ m[(?:.{$N})*(?=($key\G..))]g;
}
[download]

And I cannot make it work. (The above silently matches nothing; v-e-r-y s-l-o-w-l-y!).

And that is pretty much the kind of effect I seem to get every time I try to use \G. I conclude that I have just never managed to acquire a good mental model of what it actually does; despite years of trying on and off.

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