替代字符不包含在方括号中

Question

I have a string containing curly brackets and I want to replace any character A, which is not contained in a pair of opening and closing brackets, by another character B. So

ABCDACD{ACDA}ABCD

should be replaced by

BBCDBCD{ACDA}BBCD

How can I do this with a regex (eg in Perl)? Brackets are not nested, but a solution working also for the nested case would be better.

EDIT: Changed wording

Answer 1

A similar question has already been answered before.

Perl implementation will be different in substitution evaluation part but the main idea is the same:

Match undesired context (ie {.*?} ) or desired substring ( A ) (in that particular order) using alternation capturing the matches. Then substitute the undesired capture with itself and the desired one with your replacement depending on which part has matched:

my $input = "ABCDACD{ACDA}ABCD";
$input =~ s/({.*?})|(A)/{$2 ? "B" : $1}/ge;

Demo: https://ideone.com/bK4c1Y

Answer 2

Here is a Perl solution that does the job in steps. First it splits the string into chunks of braced/not braced items. Then does the substitution on the not-braced items, and finally puts the items back together again:

my $str = 'ABCDACD{ACDA}ABCD';
$str = do {
    my $i = 1; 
    join '', map {$i++ % 2 && $_ =~ s/A/B/g; $_ } split /(\{.*?\})/, $str 
};