Mastering Embedded Linux Programming - Second Edition

Automating the boot with U-Boot scripts

Plainly, typing a long series of commands to boot your board each time it is turned on is not acceptable. To automate the process, U-Boot stores a sequence of commands in environment variables. If the special variable named bootcmd contains a script, it is run at power-up after a delay of bootdelay seconds. If you watch this on the serial console, you will see the delay counting down to zero. You can press any key during this period to terminate the countdown and enter into an interactive session with U-Boot.

The way that you create scripts is simple, though not easy to read. You simply append commands separated by semicolons, which must be preceded by a backslash escape character. So, for example, ...