I'd put . in place of ???? and then * after the first parentheses...

use v5.12;

my @should_match = (
    q[foo],
    q[WXYZfoo],
    q[WXYZWXYZfoo],
    q[WXYZ    WXYZfoo],
);

my @should_not_match = (
    q[ foo],
    q[ABCfoo],
    q[VWXYZfoo],
    q[WXYZWXYZWXYZAfoo],
);

my $regexp = qr{^(?:.{4})*foo};

say /$regexp/ ? "ok" : "not ok" for @should_match;
say /$regexp/ ? "not ok" : "ok" for @should_not_match;

[download]
package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name

In reply to Re: A regex that only matches at offset that are multiples of a given N? by tobyink
in thread A regex that only matches at offset that are multiples of a given N? by BrowserUk

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