Shell

Overview

This module allows you to create and handle a shell with a user-defined command set. You can use it in examples where more than simple button or LED user interaction is required. This module is a Unix-like shell with these features:

  • Support for multiple instances.
  • Advanced cooperation with the Logger.
  • Support for static and dynamic commands.
  • Smart command completion with the Tab key.
  • Built-in commands: clear, shell, colors, echo, history and resize.
  • Viewing recently executed commands using keys: .
  • Text edition using keys: , , Backspace, Delete, End, Home, Insert.
  • Support for ANSI escape codes: VT100 and ESC[n~ for cursor control and color printing.
  • Support for multiline commands.
  • Built-in handler to display help for the commands.
  • Support for wildcards: * and ?.
  • Support for meta keys.
  • Kconfig configuration to optimize memory usage.

The module can be connected to any transport for command input and output. At this point, the following transport layers are implemented:

  • UART
  • Segger RTT
  • DUMMY - not a physical transport layer

See the Shell system API documentation for more information.

Connecting to Segger RTT via TCP (on macOS, for example)

On macOS JLinkRTTClient won’t let you enter input. Instead, please use following procedure:

  • Open up a first Terminal window and enter:

    JLinkRTTLogger -Device NRF52840_XXAA -RTTChannel 1 -if SWD -Speed 4000 ~/rtt.log
    

    (change device if required)

  • Open up a second Terminal window and enter:

    nc localhost 19021
    
  • Now you should have a network connection to RTT that will let you enter input to the shell.

Commands

Shell commands are organized in a tree structure and grouped into the following types:

  • Root command (level 0): Gathered and alphabetically sorted in a dedicated memory section.
  • Static subcommand (level > 0): Number and syntax must be known during compile time. Created in the software module.
  • Dynamic subcommand (level > 0): Number and syntax does not need to be known during compile time. Created in the software module.

Creating commands

Use the following macros for adding shell commands:

Commands can be created in any file in the system that includes include/shell/shell.h. All created commands are available for all shell instances.

Static commands

Example code demonstrating how to create a root command with static subcommands.

Command tree with static commands.
/* Creating subcommands (level 1 command) array for command "demo". */
SHELL_CREATE_STATIC_SUBCMD_SET(sub_demo)
{
        SHELL_CMD(params, NULL, "Print params command.",
                                               cmd_demo_params),
        SHELL_CMD(ping,   NULL, "Ping command.", cmd_demo_ping),
        SHELL_SUBCMD_SET_END /* Array terminated. */
};
/* Creating root (level 0) command "demo" */
SHELL_CMD_REGISTER(demo, &sub_demo, "Demo commands", NULL);

Example implementation can be found under following location: samples/subsys/shell/shell_module/src/main.c.

Dynamic commands

Example code demonstrating how to create a root command with static and dynamic subcommands. At the beginning dynamic command list is empty. New commands can be added by typing:

dynamic add <new_dynamic_command>

Newly added commands can be prompted or autocompleted with the Tab key.

Command tree with static and dynamic commands.
/* Buffer for 10 dynamic commands */
static char dynamic_cmd_buffer[10][50];

/* commands counter */
static u8_t dynamic_cmd_cnt;

/* Function returning command dynamically created
 * in  dynamic_cmd_buffer.
 */
static void dynamic_cmd_get(size_t idx,
                            struct shell_static_entry *entry)
{
        if (idx < dynamic_cmd_cnt) {
                entry->syntax = dynamic_cmd_buffer[idx];
                entry->handler  = NULL;
                entry->subcmd = NULL;
                entry->help = "Show dynamic command name.";
        } else {
                /* if there are no more dynamic commands available
                 * syntax must be set to NULL.
                 */
                entry->syntax = NULL;
        }
}

SHELL_CREATE_DYNAMIC_CMD(m_sub_dynamic_set, dynamic_cmd_get);
SHELL_CREATE_STATIC_SUBCMD_SET(m_sub_dynamic)
{
        SHELL_CMD(add, NULL,"Add new command to dynamic_cmd_buffer and"
                  " sort them alphabetically.",
                  cmd_dynamic_add),
        SHELL_CMD(execute, &m_sub_dynamic_set,
                  "Execute a command.", cmd_dynamic_execute),
        SHELL_CMD(remove, &m_sub_dynamic_set,
                  "Remove a command from dynamic_cmd_buffer.",
                  cmd_dynamic_remove),
        SHELL_CMD(show, NULL,
                  "Show all commands in dynamic_cmd_buffer.",
                  cmd_dynamic_show),
        SHELL_SUBCMD_SET_END
};
SHELL_CMD_REGISTER(dynamic, &m_sub_dynamic,
           "Demonstrate dynamic command usage.", cmd_dynamic);

Example implementation can be found under following location: samples/subsys/shell/shell_module/src/dynamic_cmd.c.

Commands execution

Each command or subcommand may have a handler. The shell executes the handler that is found deepest in the command tree and further subcommands (without a handler) are passed as arguments. Characters within parentheses are treated as one argument. If shell wont find a handler it will display an error message.

Commands can be also executed from a user application using any active backend and a function shell_execute_cmd(), as shown in this example:

void main(void)
{
        /* Below code will execute "clear" command on a DUMMY backend */
        shell_execute_cmd(NULL, "clear");

        /* Below code will execute "shell colors off" command on
         * an UART backend
         */
        shell_execute_cmd(shell_backend_uart_get_ptr(),
                          "shell colors off");
}

Enable the DUMMY backend by setting the Kconfig CONFIG_SHELL_BACKEND_DUMMY option.

Command handler

Simple command handler implementation:

static int cmd_handler(const struct shell *shell, size_t argc,
                        char **argv)
{
        ARG_UNUSED(argc);
        ARG_UNUSED(argv);

        shell_print(shell, "Print simple text.");

        shell_warn(shell, "Print warning text.");

        shell_error(shell, "Print error text.");

        return 0;
}

Warning

Do not use function shell_fprintf() or shell print macros: shell_print, shell_info, shell_warn, shell_error outside of the command handler because this might lead to incorrect text display on the screen. If any text should be displayed outside of the command context, then use the Logger or printk function.

Command help

Every user-defined command or subcommand can have its own help description. The help for commands and subcommands can be created with respective macros: SHELL_CMD_REGISTER, SHELL_CMD_ARG_REGISTER, SHELL_CMD, and SHELL_CMD_ARG.

Shell prints this help message when you call a command or subcommand with -h or --help parameter.

Parent commands

In the subcommand handler, you can access both the parameters passed to commands or the parent commands, depending on how you index argv.

  • When indexing argv with positive numbers, you can access the parameters.
  • When indexing argv with negative numbers, you can access the parent commands.
  • The subcommand to which the handler belongs has the argv index of 0.
static int cmd_handler(const struct shell *shell, size_t argc,
                       char **argv)
{
        ARG_UNUSED(argc);

        /* If it is a subcommand handler parent command syntax
         * can be found using argv[-1].
         */
        shell_print(shell, "This command has a parent command: %s",
                      argv[-1]);

        /* Print this command syntax */
        shell_print(shell, "This command syntax is: %s", argv[0]);

        /* Print first argument */
        shell_print(shell, "%s", argv[1]);

        return 0;
}

Built-in commands

  • clear - Clears the screen.

  • history - Shows the recently entered commands.

  • resize - Must be executed when terminal width is different than 80 characters or after each change of terminal width. It ensures proper multiline text display and , , End, Home keys handling. Currently this command works only with UART flow control switched on. It can be also called with a subcommand:

    • default - Shell will send terminal width = 80 to the terminal and assume successful delivery.
  • shell - Root command with useful shell-related subcommands like:

    • echo - Toggles shell echo.
    • colors - Toggles colored syntax. This might be helpful in case of Bluetooth shell to limit the amount of transferred bytes.
    • stats - Shows shell statistics.

Wildcards

The shell module can handle wildcards. Wildcards are interpreted correctly when expanded command and its subcommands do not have a handler. For example, if you want to set logging level to err for the app and app_test modules you can execute the following command:

log enable err a*
Wildcard usage example

Meta keys

The shell module supports the following meta keys:

Implemented meta keys
Meta keys Action
ctrl + a Moves the cursor to the beginning of the line.
ctrl + c Preserves the last command on the screen and starts a new command in a new line.
ctrl + e Moves the cursor to the end of the line.
ctrl + l Clears the screen and leaves the currently typed command at the top of the screen.
ctrl + u Clears the currently typed command.
ctrl + w Removes the word or part of the word to the left of the cursor. Words separated by period instead of space are treated as one word.

Usage

To create a new shell instance user needs to activate requested backend using menuconfig.

The following code shows a simple use case of this library:

void main(void)
{

}

static int cmd_demo_ping(const struct shell *shell, size_t argc,
                         char **argv)
{
        ARG_UNUSED(argc);
        ARG_UNUSED(argv);

        shell_print(shell, "pong");
        return 0;
}

static int cmd_demo_params(const struct shell *shell, size_t argc,
                           char **argv)
{
        int cnt;

        shell_print(shell, "argc = %d", argc);
        for (cnt = 0; cnt < argc; cnt++) {
                shell_print(shell, "  argv[%d] = %s", cnt, argv[cnt]);
        }
        return 0;
}

/* Creating subcommands (level 1 command) array for command "demo". */
SHELL_CREATE_STATIC_SUBCMD_SET(sub_demo)
{
        SHELL_CMD(params, NULL, "Print params command.",
                                               cmd_demo_params),
        SHELL_CMD(ping,   NULL, "Ping command.", cmd_demo_ping),
        SHELL_SUBCMD_SET_END /* Array terminated. */
};
/* Creating root (level 0) command "demo" without a handler */
SHELL_CMD_REGISTER(demo, &sub_demo, "Demo commands", NULL);

/* Creating root (level 0) command "version" */
SHELL_CMD_REGISTER(version, NULL, "Show kernel version", cmd_version);

Users may use the Tab key to complete a command/subcommand or to see the available subcommands for the currently entered command level. For example, when the cursor is positioned at the beginning of the command line and the Tab key is pressed, the user will see all root (level 0) commands:

clear  demo  shell  history  log  resize  version

Note

To view the subcommands that are available for a specific command, you must first type a space after this command and then hit Tab.

These commands are registered by various modules, for example:

  • clear, shell, history, and resize are built-in commands which have been registered by subsys/shell/shell.c
  • demo and version have been registered in example code above by main.c
  • log has been registered by subsys/logging/log_cmds.c

Then, if a user types a demo command and presses the Tab key, the shell will only print the subcommands registered for this command:

params  ping