shell: Add rtems_shell_run_main_loop()

In contrast to rtems_shell_main_loop(), this new function does not
perform all sorts of initialization based on environment settings.  For
example, due to the use of isatty() in rtems_shell_main_loop() it is
impossible to run an interactive shell through a socket connection.

cpukit/include/rtems/shell.h

@@ -254,6 +254,31 @@ bool rtems_shell_main_loop(
   rtems_shell_env_t *rtems_shell_env
 );
 
+/**
+ * @brief Runs the shell main loop.
+ *
+ * The caller shall initialize the shell environment.  It is recommended that
+ * the caller duplicates the current shell environment using
+ * rtems_shell_dup_current_env() and then performs the required customization.
+ * Shell commands will use the stdin, stdout, and stderr file streams set up by
+ * the caller.
+ *
+ * @param interactive indicates if the shell main loop interfaces with an
+ *   interactive user.  For an interactive user, a welcome message using
+ *   "/etc/motd" is presented and command prompt is displayed.
+ *
+ * @param[in, out] line_editor_output is the optional line editor output file
+ *   stream.  It may be NULL, to disable the line editor output.
+ *
+ * @return Returns true, if no error occurred and a shell exit was requested,
+ *   otherwise false.
+ */
+bool rtems_shell_run_main_loop(
+  rtems_shell_env_t *shell_env,
+  bool               interactive,
+  FILE              *line_editor_output
+);
+
 extern const rtems_shell_env_t rtems_global_shell_env;
 
 rtems_shell_env_t *rtems_shell_get_current_env(void);

cpukit/libmisc/shell/shell.c

@@ -1010,6 +1010,31 @@ static bool shell_main_loop(
   return result;
 }
 
+bool rtems_shell_run_main_loop(
+  rtems_shell_env_t *shell_env,
+  bool               interactive,
+  FILE              *line_editor_output
+)
+{
+  bool result;
+
+  if (shell_env->magic != SHELL_MAGIC) {
+    return false;
+  }
+
+  if (!rtems_shell_init_user_env()) {
+    return false;
+  }
+
+  if (!rtems_shell_set_shell_env(shell_env)) {
+    return false;
+  }
+
+  result = shell_main_loop(shell_env, interactive, line_editor_output);
+  rtems_shell_clear_shell_env();
+  return result;
+}
+
 bool rtems_shell_main_loop(
   rtems_shell_env_t *shell_env
 )