for my $string ('CN=ext.Group.eso,OU=External,OU=ExDistriGroups,OU=Accounts,DC=eso,DC=local',
                'CN=ext.Group.test,OU=External,OU=ExDistriGroups,OU=Accounts,DC=eso,DC=local',
                'CN=ext.Group."MY TERM",OU=External,OU=ExDistriGroups,OU=Accounts,DC=eso,DC=local',
               ) {
    my ($term) = $string =~ /CN=ext\.Group\.([^,]+)/;
    print "Found: $term\n";
}