This is how you can replace hash tag with forward slashes in url

replash_hash_tag_url.dart

void main() {
  String text = "Test #/first1hashtag test #/second2hashtag test.";
  RegExp exp = new RegExp(r"\B#\/");
  exp.allMatches(text).forEach((match){
    print(match.group(0));
    text = text.replaceAll(match.group(0), "");
  });
  print(text);
  
  String text2 = "Test #/first1hashtag test #/second2hashtag test.";
  text2 = text2.replaceAll("#/", "");
  print(text2);
}