What you and I and, it seems, everyone else are missing is a clear understanding of BernieC's requirements.

What I understand (or imagine I understand) is that one must detect repetition only of a set of characters given in a "template" string. So if the template is 'abc', the string 'xxxabcxxx' has no repetition and the string 'aba' does. See Re^3: Nonrepeating characters in an RE (updated) and Re: Nonrepeating characters in an RE (updated) for my take on solutions to what I imagine BernieC's requirements to be.

Well, in that case...

my @test = qw/xyzabcxxx xyzaabxxx xyzabbxxx xyzabaxxx/;

for (@test) {
    # only check for 'abc'
    say if not /([abc]).*?\1/;
}
[download]

Still quite simple, isn't it?

> Still quite simple, isn't it

Yes and not new at all.

Re^3: Nonrepeating characters in an RE (simple)

And now try to include it into a larger regex where it only handles a small part.

You can try to contact BernieC to find out how this substring is defined.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery}