shell: Add shell_exec

This adds shell_exec which can be used to execute commands directly
without the use of a console which is useful for both testing as well
as interfacing with applications/upper layer which would like to have
access to shell commands directly.

In addition to that this may be more trivial to interface with instead
of using fifos like uart_register_input and telnet_register_input do.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

include/shell/shell.h

@@ -119,6 +119,22 @@ void shell_register_prompt_handler(shell_prompt_function_t handler);
  */
 void shell_register_default_module(const char *name);
 
+/** @brief Execute command line.
+ *
+ *  Pass command line to shell to execute. The line cannot be a C string literal
+ *  since it will be modified in place, instead a variable can be used:
+ *
+ *    char cmd[] = "command";
+ *    shell_exec(cmd);
+ *
+ *  Note: This by no means makes any of the commands a stable interface, so
+ *  this function should only be used for debugging/diagnostic.
+ *
+ *  @param line Command line to be executed
+ *  @returns Result of the execution
+ */
+int shell_exec(char *line);
+
 /**
 * @}
 */