Select Code to Download

my @tst = qw(   A,G AG,CT TC,CA GAT,CGA CGAT,TG ,G
                ACGT X,A AA,G AC,GGC ATGA,TGG ATCXG,AAC
...
        my $side = qr/(?:([ACGT])(?![^,]*\g{-1}))+/;
        print $_ . (/^$side,$side$/ ? ' good' : ' bad') . $/;
}

A,G good
AG,CT good
...
AC,GGC bad
ATGA,TGG bad
ATCXG,AAC bad