[U-Boot] u-boot environment variable parsing
Hi,
I need one clarification regarding Environment variable declaration & its usage.
#define CONFIG_EXTRA_ENV_SETTINGS \ "brd_mem=62M\0" \ "bootargs_defaults=setenv bootargs " \ "console=${console} " \ "mem=${brd_mem}\0" \ "mmc_args=run bootargs_defaults;" \ "setenv bootargs $(bootargs) " \ "root=${mmc_root} " \ "rootfstype=${mmc_root_fs_type} ip=${ip_method}\0" \ "nand_args=run bootargs_defaults;" \ "setenv bootargs ${bootargs} " \ "root=${nand_root} noinitrd " \ "rootfstype=${nand_root_fs_type} ip=${ip_method}\0" \
The question here is mmc_args re-uses variable bootargs as $(bootargs) & nand_args re-uses it as ${bootargs}. Note the difference in curly & flower brackets. "run mmc_args" fails for me however nand_args runs properly.
My question is 1. Which is correct? 2. What is the difference between the two?
I have seen few boards using both methods.
Thanks in advance
Regards Gururaja
Dear "Hebbar, Gururaja",
In message C82BA3053CFD354AACBD25EFBD2A4EC603F0193C2D@dbde02.ent.ti.com you wrote:
The question here is mmc_args re-uses variable bootargs as $(bootargs) & nand_args re-uses it as ${bootargs}. Note the difference in curly & flower brackets. "run mmc_args" fails for me however nand_args runs properly.
Does this not answer your question sufficiently?
My question is
- Which is correct?
${...} is correct.
- What is the difference between the two?
${...} is correct, and $(...) is not correct.
I have seen few boards using both methods.
$(...) was used in very old versions of U-Boot, but this got changed for the sake of compatibility with standard shell syntax.
Note that the simple cmmand line parser still accepts the obsolete $(...) format; the hush shell doesn't.
Best regards,
Wolfgang Denk
Hi wd,
Thanks for the reply. Helped me a lot.
However see below
On Thu, Jul 21, 2011 at 18:41:30, Wolfgang Denk wrote:
Dear "Hebbar, Gururaja",
In message C82BA3053CFD354AACBD25EFBD2A4EC603F0193C2D@dbde02.ent.ti.com you wrote:
The question here is mmc_args re-uses variable bootargs as $(bootargs) & nand_args re-uses it as ${bootargs}. Note the difference in curly & flower brackets. "run mmc_args" fails for me however nand_args runs properly.
Does this not answer your question sufficiently?
The point is mmc_args worked in one place & failed in other. After you reply, I found that the place where it worked was common shell environment & it was failing in Hush shell.
My question is
- Which is correct?
${...} is correct.
- What is the difference between the two?
${...} is correct, and $(...) is not correct.
I have seen few boards using both methods.
$(...) was used in very old versions of U-Boot, but this got changed for the sake of compatibility with standard shell syntax.
Note that the simple cmmand line parser still accepts the obsolete $(...) format; the hush shell doesn't.
Best regards,
Wolfgang Denk
-- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de A morsel of genuine history is a thing so rare as to be always valuable. - Thomas Jefferson
Regards, Gururaja
participants (2)
-
Hebbar, Gururaja -
Wolfgang Denk