I don't see a need for a look ahead. Try:

#!/usr/bin/perl
use warnings;
use strict;

for my $test (
    'https://www.robidu.de/', 'http://www.robidu.de/',
    'https://robidu.de/',     'https://forum.robidu.de/'
    )
{
    if ($test =~ m~^https?://(?:www\.)?robidu\.de/~) {
        print "'$test' matched\n";
    } else {
        print "'$test' didn't match\n";
    }
}

[download]

Prints:

'https://www.robidu.de/' matched
'http://www.robidu.de/' matched
'https://robidu.de/' matched
'https://forum.robidu.de/' didn't match

[download]
Premature optimization is the root of all job security

In reply to Re: regexp: Mind-boggling negative assertions... by GrandFather
in thread regexp: Mind-boggling negative assertions... by Robidu

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