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:
This takes very little code space and offers only basic features:
- supports environment variables (through
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'
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.
- 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.
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