The shell runs above the console and provides two functionalities:

The shell uses the OS default event queue for shell events and runs in the context of the main task. An application can, optionally, specify a dedicated event queue for the shell to use.

The sys/shell package implements the shell. To use the shell you must:

  • Include the sys/shell package.
  • Set the SHELL_TASK syscfg setting value to 1 to enable the shell.

Note: The functions for the shell API are only compiled and linked with the application when the SHELL_TASK setting is enabled. When you develop a package that supports shell commands, we recommend that your pakcage define:

  1. A syscfg setting that enables shell command processing for your package, with a restriction that when this setting is enabled, the SHELL_TASK setting must also be enabled.
  2. A conditional dependency on the sys/shell package when the setting defined in 1 above is enabled.

Here are example definitions from the syscfg.yml and pkg.yml files for the sys/log/full package. It defines the LOG_CLI setting to enable the log command in the shell:

# sys/log/full syscfg.yml
        description: 'Expose "log" command in shell.'
        value: 0
            - SHELL_TASK

# sys/log/full pkg.yml
    - sys/shell


Processing Console Input Commands

The shell's first job is to direct incoming commands to other subsystems. It parses the incoming character string into tokens and uses the first token to determine the subsystem command handler to call to process the command. When the shell calls the command handler, it passes the other tokens as arguments to the handler.

Registering Command Handlers

A package that implements a shell command must register a command handler to process the command.

New in release 1.1: The shell supports the concept of modules and allows a package to group shell commands under a name space. To run a command in the shell, you enter the module name and the command name. You can set a default module, using the select command, so that you only need to enter the command name to run a command from the default module. You can switch the module you designate as the default module.

There are two methods to register command handlers in Mynewt 1.1:

  • Method 1 (New in release 1.1): Define and register a set of commands for a module. This method allows grouping shell commands into namespaces. A package calls the shell_register() function to define a module and register the command handlers for the module.

    Note: The SHELL_MAX_MODULES syscfg setting specifies the maximum number of modules that can be registered. You can increase this value if your application and the packages it includes register more than the default value.

  • Method 2: Register a command handler without defining a module. A package calls the shell_cmd_register() function defined in Mynewt 1.0 to register a command handler. When a shell command is registered using this method, the command is automatically added to the compat module. The compat module supports backward compatibility for all the shell commands that are registered using the shell_cmd_register() function.


    • The SHELL_COMPAT syscfg setting must be set to 1 to enable backward compatibility support and the shell_cmd_register() function. Since Mynewt packages use method 2 to register shell commands and Mynewt plans to continue this support in future releases, you must keep the default setting value of 1.

    • The SHELL_MAX_COMPAT_COMMANDS syscfg setting specifies the maximum number of command handlers that can be registered using this method. You can increase this value if your application and the packages it includes register more than the default value.

Enabling Help Information for Shell Commands

The shell supports command help. A package that supports command help initializes the struct shell_cmd data structure with help text for the command before it registers the command with the shell. The SHELL_CMD_HELP syscfg setting enables or disbles help support for all shell commands. The feature is enabled by default.

Note: A package that implements help for a shell command should only initialize the help data structures within the #if MYNEWT_VAL(SHELL_CMD_HELP) preprocessor directive.

Enabling the OS and Prompt Shell Modules

The shell implements the os and prompt modules. These modules support the shell commands to view OS resources.

The os module implements commands to list task and mempool usage information and to view and change the time of day. The SHELL_OS_MODULE syscfg setting enables or disables the module. The module is enabled by default.

The prompt module implements the ticks command that controls whether to print the current os ticks in the prompt. The SHELL_PROMPT_MODULE syscfg setting enables or disables this module. The module is disabled by default.

Enabling Command Name Completion

The shell supports command name completion. The SHELL_COMPLETION syscfg setting enables or disables the feature. The feature is enabled by default.

Processing Newtmgr Line Protocol Over Serial Transport

The shell's second job is to handle packet framing, encoding, and decoding of newtmgr protocol messages that are sent over the console. The Newtmgr serial transport package (mgmt/newtmgr/transport/newtmgr_shell) calls the shell_nlip_input_register() function to register a handler that the shell calls when it receives newtmgr request messages.

The SHELL_NEWTMGR syscfg setting specifies whether newtmgr is enabled over shell. The setting is enabled by default.

Data Structures

The struct shell_cmd data structure represents a shell command and is used to register a command.

struct shell_cmd {
    const char *sc_cmd;
    shell_cmd_func_t sc_cmd_func;
    const struct shell_cmd_help *help;
Element Description
sc_cmd Character string of the command name.
sc_cmd_func_t Pointer to the command handler that processes the command.
help Pointer to the shell_cmd_help structure. If the pointer is NULL, help information is not provided.

The sc_cmd_func_t is the command handler function type.

typedef int (*shell_cmd_func_t)(int argc, char *argv[]);

The argc parameter specifies the number of command line arguments and the argv parameter is an array of character pointers to the command arguments. The SHELL_CMD_ARGC_MAX syscfg setting specifies the maximum number of command line arguments that any shell command can have. This value must be increased if a shell command requires more than SHELL_CMD_ARGC_MAX number of command line arguments.

The struct shell_module data structure represents a shell module. It is used to register a shell module and the shell commands for the module.

struct shell_module {
    const char *name;
    const struct shell_cmd *commands;
Element Description
name Character string of the module name.
commands Array of shell_cmd structures that specify the commands for the module. The sc_cmd, sc_cmd_func, and help fields in the last entry must be set to NULL to indicate the last entry in the array.

Note: A command handler registered via the shell_cmd_register() function is automatically added to the compat module.

The struct shell_param and struct shell_cmd_help data structures hold help texts for a shell command.

struct shell_param {
    const char *param_name;
    const char *help;
Element Description
param_name Character string of the command parameter name.
help Character string of the help text for the parameter.

struct shell_cmd_help {
    const char *summary;
    const char *usage;
    const struct shell_param *params;
Element Description
summary Character string of a short description of the command.
usage Character string of a usage description for the command.
params Array of shell_param structures that describe each parameter for the command. The last struct shell_param in the array must have the param_name and help fields set to NULL to indicate the last entry in the array.

List of Functions

The functions available in this OS feature are:

Function Description
shell_cmd_register Registers a handler for incoming console commands.
shell_evq_set Specifies a dedicated event queue for shell events.
shell_nlip_input_register Registers a handler for incoming newtmgr messages.
shell_nlip_output Queue outgoing newtmgr message for transmission.
shell_register Registers a shell module and the commands for the module.
shell_register_app_cmd_handler Registers a command handler as an application handler. The shell calls this handler when a command does not have a handler registered.
shell_register_default_module Registers a module with a specified name as the default module.