The join statement in the test matches non-period data and joins it back together before it is matched as normal.

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

my $lookfor = "xyz123abc";
while (<DATA>) {
    chomp;
    print "$_ matched\n" if join('', /([^\.]+)/g) =~ /^$lookfor$/;
}

__DATA__
xyz123abc
xy.z123abc
xyz1.23.abc
xyz123abc1
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