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 setenv / saveenv commands)

  • 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:

  • ifthenelsefi
  • fordodone
  • whiledodone
  • untildodone

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

  1. 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.
  2. 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.

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