Console

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

  • 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 useful for parsing GNU style command line arguments.
  • Functions for registration and dispatching of commands.

These facilities 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.

Line editing

Line editing feature lets users compose commands by typing them, erasing symbols using ‘backspace’ key, navigating within the command using left/right keys, navigating to previously typed commands using up/down keys, and performing autocompletion using ‘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 get_started/console example instead of a command prompt ([esp32]>), it means that the serial monitor does not support escape sequences. Programs which are known to work are GNU screen, minicom, and idf_monitor.py (which can be invoked using make 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.

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

Main loop

linenoise
In most cases, console applications have some form of read/eval loop. linenoise is the single function which handles user’s key presses and returns completed line once ‘enter’ key is pressed. As such, it handles the ‘read’ part of the loop.
linenoiseFree
This function must be called to release the command line buffer obtained from linenoise function.

Hints and completions

linenoiseSetCompletionCallback

When user presses ‘tab’ key, linenoise library invokes completion callback. The callback should inspect the contents of the command typed so far and provide a list of possible completions using calls to linenoiseAddCompletion function. linenoiseSetCompletionCallback 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, esp_console_get_completion (see below).

linenoiseAddCompletion
Function to be called by completion callback to inform the library about possible completions of the currently typed command.
linenoiseSetHintsCallback
Whenever user input changes, linenoise invokes 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.
linenoiseSetFreeHintsCallback
If 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 linenoiseSetFreeHintsCallback.

History

linenoiseHistorySetMaxLen
This function sets the number of most recently typed commands to be kept in memory. Users can navigate the history using up/down arrows.
linenoiseHistoryAdd
Linenoise does not automatically add commands to history. Instead, applications need to call this function to add command strings to the history.
linenoiseHistorySave
Function saves command history from RAM to a text file, for example on an SD card or on a filesystem in flash memory.
linenoiseHistoryLoad
Counterpart to linenoiseHistorySave, loads history from a file.
linenoiseHistoryFree
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 esp_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 esp_console_init, and calls esp_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.
  • The command handler function.

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

esp_console_run
This function takes the command line string, splits it into argc/argv argument list using esp_console_split_argv, looks up the command in the list of registered components, and if it is found, executes its handler.
esp_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.
esp_console_get_completion
Callback function to be used with linenoiseSetCompletionCallback from linenoise library. Provides completions to linenoise based on the list of registered commands.
esp_console_get_hint
Callback function to be used with linenoiseSetHintsCallback from linenoise library. Provides argument hints for registered commands to linenoise.

Example

Example application illustrating usage of the console component is available in examples/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.