console.rst

Console

:link_to_translation:zh_CN:[中文]

ESP-IDF provides console component, which includes building blocks needed to develop an interactive console over serial port. This component includes the following features:

• Line editing, provided by linenoise library. This includes handling of backspace and arrow keys, scrolling through command history, command auto-completion, and argument hints.
• Splitting of command line into arguments.
• Argument parsing, provided by argtable3 library. This library includes APIs used for parsing GNU style command line arguments.
• Functions for registration and dispatching of commands.
• Functions to establish a basic REPL (Read-Evaluate-Print-Loop) environment.

Note

These features can be used together or independently. For example, it is possible to use line editing and command registration features, but use getopt or custom code for argument parsing, instead of argtable3. Likewise, it is possible to use simpler means of command input (such as fgets) together with the rest of the means for command splitting and argument parsing.

Note

When using a console application on a chip that supports a hardware USB serial interface, we suggest to disable the secondary serial console output. The secondary output will be output-only and consequently does not make sense in an interactive application.

Line Editing

Line editing feature lets users compose commands by typing them, erasing symbols using the backspace key, navigating within the command using the left/right keys, navigating to previously typed commands using the up/down keys, and performing autocompletion using the tab key.

Note

This feature relies on ANSI escape sequence support in the terminal application. As such, serial monitors which display raw UART data can not be used together with the line editing library. If you see [6n or similar escape sequence when running system/console example instead of a command prompt (e.g., esp> ), it means that the serial monitor does not support escape sequences. Programs which are known to work are GNU screen, minicom, and esp-idf-monitor (which can be invoked using idf.py monitor from project directory).

Here is an overview of functions provided by linenoise library.

Configuration

Linenoise library does not need explicit initialization. However, some configuration defaults may need to be changed before invoking the main line editing function.

• :cpplinenoiseClearScreen

  Clear terminal screen using an escape sequence and position the cursor at the top left corner.

• :cpplinenoiseSetMultiLine

  Switch between single line and multi line editing modes. In single line mode, if the length of the command exceeds the width of the terminal, the command text is scrolled within the line to show the end of the text. In this case the beginning of the text is hidden. Single line mode needs less data to be sent to refresh screen on each key press, so exhibits less glitching compared to the multi line mode. On the flip side, editing commands and copying command text from terminal in single line mode is harder. Default is single line mode.

• :cpplinenoiseAllowEmpty

  Set whether linenoise library returns a zero-length string (if true) or NULL (if false) for empty lines. By default, zero-length strings are returned.

• :cpplinenoiseSetMaxLineLen

  Set maximum length of the line for linenoise library. Default length is 4096 bytes. The default value can be updated to optimize RAM memory usage.

Main Loop

• :cpplinenoise

  In most cases, console applications have some form of read/eval loop. :cpplinenoise is the single function which handles user's key presses and returns the completed line once the enter key is pressed. As such, it handles the read part of the loop.

• :cpplinenoiseFree

  This function must be called to release the command line buffer obtained from :cpplinenoise function.

Hints and Completions

• :cpplinenoiseSetCompletionCallback

  When the user presses the tab key, linenoise library invokes the completion callback. The callback should inspect the contents of the command typed so far and provide a list of possible completions using calls to :cpplinenoiseAddCompletion function. :cpplinenoiseSetCompletionCallback function should be called to register this completion callback, if completion feature is desired.

  console component provides a ready made function to provide completions for registered commands, :cppesp_console_get_completion (see below).

• :cpplinenoiseAddCompletion

  Function to be called by completion callback to inform the library about possible completions of the currently typed command.

• :cpplinenoiseSetHintsCallback

  Whenever user input changes, linenoise invokes the hints callback. This callback can inspect the command line typed so far, and provide a string with hints (which can include list of command arguments, for example). The library then displays the hint text on the same line where editing happens, possibly with a different color.

• :cpplinenoiseSetFreeHintsCallback

  If the hint string returned by hints callback is dynamically allocated or needs to be otherwise recycled, the function which performs such cleanup should be registered via :cpplinenoiseSetFreeHintsCallback.

History

• :cpplinenoiseHistorySetMaxLen

  This function sets the number of most recently typed commands to be kept in memory. Users can navigate the history using the up/down arrows keys.

• :cpplinenoiseHistoryAdd

  Linenoise does not automatically add commands to history. Instead, applications need to call this function to add command strings to the history.

• :cpplinenoiseHistorySave

  Function saves command history from RAM to a text file, for example on an SD card or on a filesystem in flash memory.

• :cpplinenoiseHistoryLoad

  Counterpart to :cpplinenoiseHistorySave, loads history from a file.

• :cpplinenoiseHistoryFree

  Releases memory used to store command history. Call this function when done working with linenoise library.

Splitting of Command Line into Arguments

console component provides :cppesp_console_split_argv function to split command line string into arguments. The function returns the number of arguments found (argc) and fills an array of pointers which can be passed as argv argument to any function which accepts arguments in argc, argv format.

The command line is split into arguments according to the following rules:

• Arguments are separated by spaces
• If spaces within arguments are required, they can be escaped using \ (backslash) character.
• Other escape sequences which are recognized are \\ (which produces literal backslash) and \", which produces a double quote.
• Arguments can be quoted using double quotes. Quotes may appear only in the beginning and at the end of the argument. Quotes within the argument must be escaped as mentioned above. Quotes surrounding the argument are stripped by esp_console_split_argv function.

Examples:

• abc def 1 20 .3 > [ abc, def, 1, 20, .3 ]
• abc "123 456" def > [ abc, 123 456, def ]
• `a\ b\\c\" > [ a b\c" ]

Argument Parsing

For argument parsing, console component includes argtable3 library. Please see tutorial for an introduction to argtable3. Github repository also includes examples.

Command Registration and Dispatching

console component includes utility functions which handle registration of commands, matching commands typed by the user to registered ones, and calling these commands with the arguments given on the command line.

Application first initializes command registration module using a call to :cppesp_console_init, and calls :cppesp_console_cmd_register function to register command handlers.

For each command, application provides the following information (in the form of esp_console_cmd_t structure):

• Command name (string without spaces)
• Help text explaining what the command does
• Optional hint text listing the arguments of the command. If application uses Argtable3 for argument parsing, hint text can be generated automatically by providing a pointer to argtable argument definitions structure instead.
• Command handler function (without context), or
• Command handler function (with context). If this function is given, an additional call to :cppesp_console_cmd_set_context must follow before the command may be called to initialize the context.

Note

You can either use a command handler function which takes a context or a command handler function which does not take a context, not both. If you use the command handler function which takes a context, you MUST call :cppesp_console_cmd_set_context to initialize its context, otherwise the function may access the uninitialized context.

A few other functions are provided by the command registration module:

• :cppesp_console_run

  This function takes the command line string, splits it into argc/argv argument list using :cppesp_console_split_argv, looks up the command in the list of registered components, and if it is found, executes its handler.

• :cppesp_console_register_help_command

  Adds help command to the list of registered commands. This command prints the list of all the registered commands, along with their arguments and help texts.

• :cppesp_console_get_completion

  Callback function to be used with :cpplinenoiseSetCompletionCallback from linenoise library. Provides completions to linenoise based on the list of registered commands.

• :cppesp_console_get_hint

  Callback function to be used with :cpplinenoiseSetHintsCallback from linenoise library. Provides argument hints for registered commands to linenoise.

Initialize Console REPL Environment

To establish a basic REPL environment, console component provides several useful APIs, combining those functions described above.

In a typical application, you only need to call :cppesp_console_new_repl_uart to initialize the REPL environment based on UART device, including driver install, basic console configuration, spawning a thread to do REPL task and register several useful commands (e.g., help).

After that, you can register your own commands with :cppesp_console_cmd_register. The REPL environment keeps in init state until you call :cppesp_console_start_repl.

SOC_USB_SERIAL_JTAG_SUPPORTED

Likewise, if your REPL environment is based on USB_SERIAL_JTAG device, you only need to call :cppesp_console_new_repl_usb_serial_jtag at first step. Then call other functions as usual.

Application Example

Example application illustrating usage of the console component is available in system/console directory. This example shows how to initialize UART and VFS functions, set up linenoise library, read and handle commands from UART, and store command history in Flash. See README.md in the example directory for more details.

Besides that, ESP-IDF contains several useful examples which are based on the console component and can be treated as "tools" when developing applications. For example, peripherals/i2c/i2c_tools, wifi/iperf.

API Reference

inc/esp_console.inc