add star_subst() utility function that replaces a '*' in a string with a number

src/utils.cpp

@@ -791,11 +791,23 @@ std::string utils::trim(const std::string &line)
 
 std::string utils::trim_comment(const std::string &line)
 {
-  auto end = line.find_first_of('#');
+  auto end = line.find('#');
   if (end != std::string::npos) { return line.substr(0, end); }
   return {line};
 }
 
+/* ----------------------------------------------------------------------
+   Replace '*' with number and optional zero-padding
+------------------------------------------------------------------------- */
+
+std::string utils::star_subst(const std::string &name, bigint step, int pad)
+{
+  auto star = name.find('*');
+  if (star == std::string::npos) return name;
+
+  return fmt::format("{}{:0{}}{}",name.substr(0,star),step,pad,name.substr(star+1));
+}
+
 /* ----------------------------------------------------------------------
    Replace UTF-8 encoded chars with known ASCII equivalents
 ------------------------------------------------------------------------- */