sub compatible {
    my ($s1, $s2) = @_;
    my $m = length($s1) - 1;
    ($s1 . $s2) !~ /^.{0,$m}?([^_]).{$m}(?!\1)[^_]/;
}

printf "%s v %s ? %s\n", @$_, compatible( @$_ ) ? 1 : 0
        for [ qw[ _8__3__19 48____7__ ] ],  # compat
                [ qw[ _8__3__19 4_8___7__ ] ],  # compat
                [ qw[ _8__3__19 48_____7_ ] ];  # clash