diff --git a/doc/src/Developer_utils.rst b/doc/src/Developer_utils.rst
index 720eececcc..9c6ef67945 100644
--- a/doc/src/Developer_utils.rst
+++ b/doc/src/Developer_utils.rst
@@ -133,6 +133,9 @@ and parsing files or arguments.
 .. doxygenfunction:: trim_comment
    :project: progguide
 
+.. doxygenfunction:: star_subst
+   :project: progguide
+
 .. doxygenfunction:: has_utf8
    :project: progguide
 
diff --git a/src/utils.cpp b/src/utils.cpp
index ed119db886..871baf0645 100644
--- a/src/utils.cpp
+++ b/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
 ------------------------------------------------------------------------- */
diff --git a/src/utils.h b/src/utils.h
index 6811dbe874..86f31508e7 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -368,13 +368,27 @@ namespace utils {
 
   std::string trim(const std::string &line);
 
-  /*! Return string with anything from '#' onward removed
+  /*! Return string with anything from the first '#' character onward removed
    *
    * \param line  string that should be trimmed
    * \return new string without comment (string) */
 
   std::string trim_comment(const std::string &line);
 
+  /*! Replace first '*' character in a string with a number, optionally zero-padded
+   *
+   * If there is no '*' character in the string, return the original string.
+   * If the number requires more characters than the value of the *pad*
+   * argument, do not add zeros; otherwise add as many zeroes as needed to
+   * the left to make the the number representation *pad* characters wide.
+   *
+   * \param name  string with file containing a '*' (or not)
+   * \param step  step number to replace the (first) '*'
+   * \param pad   zero-padding (may be zero)
+   * \return  processed string */
+
+  std::string star_subst(const std::string &name, bigint step, int pad);
+
   /*! Check if a string will likely have UTF-8 encoded characters
    *
    * UTF-8 uses the 7-bit standard ASCII table for the first 127 characters and
diff --git a/unittest/utils/test_utils.cpp b/unittest/utils/test_utils.cpp
index dccbdb4118..900ce6814c 100644
--- a/unittest/utils/test_utils.cpp
+++ b/unittest/utils/test_utils.cpp
@@ -78,6 +78,25 @@ TEST(Utils, trim_comment)
     ASSERT_THAT(trimmed, StrEq("some text "));
 }
 
+TEST(Utils, star_subst)
+{
+    std::string starred = "beforeafter";
+    std::string subst   = utils::star_subst(starred, 1234, 0);
+    ASSERT_THAT(subst, StrEq("beforeafter"));
+
+    starred = "before*after";
+    subst   = utils::star_subst(starred, 1234, 6);
+    ASSERT_THAT(subst, StrEq("before001234after"));
+
+    starred = "before*";
+    subst   = utils::star_subst(starred, 1234, 0);
+    ASSERT_THAT(subst, StrEq("before1234"));
+
+    starred = "*after";
+    subst   = utils::star_subst(starred, 1234, 2);
+    ASSERT_THAT(subst, StrEq("1234after"));
+}
+
 TEST(Utils, has_utf8)
 {
     const char ascii_string[] = " -2";