U-Boot

.. SPDX-License-Identifier: GPL-2.0+

Command-line Parsing
====================

The command line is available in U-Boot proper, enabled by CONFIG_CMDLINE which
is on by default. It is not enabled in SPL.

There are two different command-line parsers available with U-Boot:
the old "simple" one, and the much more powerful "hush" shell:

Simple command-line parser
--------------------------

This takes very little code space and offers only basic features:

- supports environment variables (through :doc:`cmd/env`)
- several commands on one line, separated by ';'
- variable substitution using "... ${name} ..." syntax
- special characters ('$', ';') can be escaped by prefixing with '\',
  for example::

    setenv bootcmd bootm \${address}

- You can also escape text by enclosing in single apostrophes, for example::

    setenv addip 'setenv bootargs $bootargs ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off'

Hush shell
----------

This is similar to Bourne shell, with control structures like:

- `if`... `then` ... `else`... `fi`
- `for`... `do` ... `done`
- `while` ... `do` ... `done`
- `until` ... `do` ... `done`

Hush supports environment ("global") variables (through setenv / saveenv
commands) and local shell variables (through standard shell syntax
`name=value`); only environment variables can be used with the "run" command

The Hush shell is enabled with `CONFIG_HUSH_PARSER`.

General rules
-------------

#. If a command line (or an environment variable executed by a "run"
   command) contains several commands separated by semicolon, and
   one of these commands fails, then the remaining commands will be
   executed anyway.

#. If you execute several variables with one call to run (i. e.
   calling run with a list of variables as arguments), any failing
   command will cause "run" to terminate, i. e. the remaining
   variables are not executed.

#. The variable ``$?`` will be set as the return value of any command. The
   possible values are 0 on success or 1 on any error e. g. invalid syntax or
   failure of the command. Any exceptions to this are documented by the
   specific command, e.g. the :doc:`for command <cmd/for>` sets ``$?`` based on
   the last command run within the loop.

Representing numbers
--------------------

Most U-Boot commands use hexadecimal (hex) as the default base, for convenient
use of addresses, for example::

  => md 1000 6
  00001000: 2c786f62 00697073 03000000 0c000000  box,spi.........
  00001010: 67020000 00000000                    ...g....

There is no need to add a `0x` prefix to the arguments and the output is shown
in hex also, without any prefixes. This helps to avoid clutter.

Some commands use decimal where it is more natural::

  => i2c dev 0
  Setting bus to 0
  => i2c speed
  Current bus speed=400000
  => i2c speed 100000
  Setting bus speed to 100000 Hz

In some cases the default is decimal but it is possible to use octal if that is
useful::

  pmic dev pmic@41
  dev: 1 @ pmic@41
  => pmic write 2 0177
  => pmic read 2
  0x02: 0x00007f

It is possible to use a `0x` prefix to use a hex value if that is more
convenient::

  => i2c speed 0x30000
  Setting bus speed to 196608 Hz

Command-line editing
--------------------

U-Boot supports command-line editing when `CONFIG_CMDLINE_EDITING` is enabled.
This provides an Emacs-like interface for editing commands before they are
executed. The following key bindings are available:

Cursor movement
~~~~~~~~~~~~~~~

- **Left arrow** or **Ctrl+B**: Move cursor left one character
- **Right arrow** or **Ctrl+F**: Move cursor right one character
- **Ctrl+Left** or **Alt+B**: Move cursor left one word
- **Ctrl+Right** or **Alt+F**: Move cursor right one word
- **Home** or **Ctrl+A**: Move to beginning of line
- **End** or **Ctrl+E**: Move to end of line

Character deletion
~~~~~~~~~~~~~~~~~~

- **Backspace** or **Ctrl+H**: Delete character before cursor
- **Delete** or **Ctrl+D**: Delete character at cursor
- **Ctrl+K**: Kill (delete) from cursor to end of line
- **Ctrl+W**: Kill word before cursor
- **Ctrl+U**: Kill entire line
- **Ctrl+X**: Kill entire line (same as Ctrl+U)

History
~~~~~~~

- **Up arrow** or **Ctrl+P**: Previous command in history
- **Down arrow** or **Ctrl+N**: Next command in history

Undo, redo, and yank
~~~~~~~~~~~~~~~~~~~~

When `CONFIG_CMDLINE_UNDO` is enabled, the following features are available:

- **Ctrl+Z**: Undo the last edit operation
- **Ctrl+Shift+Z**: Redo the last undone operation
- **Ctrl+Y**: Yank (paste) previously killed text

Text killed by Ctrl+K, Ctrl+W, Ctrl+U, or Ctrl+X is saved to a yank buffer
and can be pasted with Ctrl+Y.

The number of undo/redo levels can be configured with `CONFIG_CMDLINE_UNDO_COUNT`
(default 1, maximum 64). Each level saves the complete buffer state,
so higher values use more memory. Note that any new edit clears the redo
history.

Other
~~~~~

- **Tab**: Command and argument completion (if `CONFIG_AUTO_COMPLETE` is enabled)
- **Ctrl+C**: Cancel current input
- **Enter**: Execute command

Multiline editing
~~~~~~~~~~~~~~~~~

In multiline mode (used by expo text editors), some keys have modified
behaviour:

- **Home/End**: Move to start/end of current line (not entire buffer)
- **Ctrl+K**: Kill to end of current line (not entire buffer)
- **Ctrl+P/N** or **Up/Down**: Navigate between lines
- **Enter**: Insert newline (instead of executing)