while (<DATA>) {
    print;
    while (/-+/g) {
        printf "Found at %s\n", $-[0]+1 . ($+[0] != $-[0]+1 ? " to $+[0]" : '');
    }
}

__DATA__
A-----B
A----C---B
A--B---C----D-E
A-B--C---D----E
---------------