29 static const std::regex expression(
"\\$(([A-Za-z0-9_]+)|\\(([A-Za-z0-9_]+)\\))" );
31 std::string result = std::string{ input };
32 auto start = input.begin();
33 auto end = input.end();
34 std::match_results<std::string_view::const_iterator> what;
35 auto flags = std::regex_constants::match_default;
36 while ( std::regex_search(
start,
end, what, expression, flags ) ) {
37 std::string var{ what[2].first, what[2].second };
38 if ( var.empty() ) var = std::string{ what[3].first, what[3].second };
41 boost::algorithm::replace_first( result, std::string{ what[0].first, what[0].second }, env );
43 start = what[0].second;
45 flags |= std::regex_constants::match_prev_avail;