[U-Boot] [PATCH] cmd_nvedit.c: Add env exists command

James Chargin
2013-10-23T13:55:02Z

Dear Andrew Ruder,

On 10/22/2013 05:07 PM, Andrew Ruder wrote:
> env exists is a way to test (in hush) if an environment variable
> exists. A workaround existed using printenv but this new command
> doesn't require all the stdout/stderr redirection to prevent
> printing information to the screen.

I was aware of the printenv workaround, and have used it. I share your
misgivings about the stdout/stderr redirection, it seems clumsy, at best.

I have, more recently, been using scripting of the form

if test "X" != "X${var}"; then
echo defined
else
echo undefined
fi

>
> Example:
> $ set testexists 1
> $ env exists testexists && echo "yes"
> yes
> $ env exists testexists || echo "no"
> $ set testexists
> $ env exists testexists && echo "yes"
> $ env exists testexists || echo "no"
> no
> $

I've often thought that a "env exists" command might be a nice,
consistent, addition.

Thanks for adding it.

Jim

>
> Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
> ---
> README | 1 +
> common/cmd_nvedit.c | 23 +++++++++++++++++++++++
> 2 files changed, 24 insertions(+)
>
> diff --git a/README b/README
> index 09662a4..0718459 100644
> --- a/README
> +++ b/README
> @@ -843,6 +843,7 @@ The following options need to be configured:
> CONFIG_CMD_ELF * bootelf, bootvx
> CONFIG_CMD_ENV_CALLBACK * display details about env callbacks
> CONFIG_CMD_ENV_FLAGS * display details about env flags
> + CONFIG_CMD_ENV_EXISTS * check existence of env variable
> CONFIG_CMD_EXPORTENV * export the environment
> CONFIG_CMD_EXT2 * ext2 command support
> CONFIG_CMD_EXT4 * ext4 command support
> diff --git a/common/cmd_nvedit.c b/common/cmd_nvedit.c
> index ba9ba16..0d4d02c 100644
> --- a/common/cmd_nvedit.c
> +++ b/common/cmd_nvedit.c
> @@ -1059,6 +1059,23 @@ sep_err:
> }
> #endif
>
> +#if defined(CONFIG_CMD_ENV_EXISTS)
> +static int do_env_exists(cmd_tbl_t *cmdtp, int flag, int argc,
> + char * const argv[])
> +{
> + ENTRY e, *ep;
> +
> + if (argc < 2)
> + return CMD_RET_USAGE;
> +
> + e.key = argv[1];
> + e.data = NULL;
> + hsearch_r(e, FIND, &ep, &env_htab, 0);
> +
> + return (ep == NULL) ? 1 : 0;
> +}
> +#endif
> +
> /*
> * New command line interface: "env" command with subcommands
> */
> @@ -1094,6 +1111,9 @@ static cmd_tbl_t cmd_env_sub[] = {
> U_BOOT_CMD_MKENT(save, 1, 0, do_env_save, "", ""),
> #endif
> U_BOOT_CMD_MKENT(set, CONFIG_SYS_MAXARGS, 0, do_env_set, "", ""),
> +#if defined(CONFIG_CMD_ENV_EXISTS)
> + U_BOOT_CMD_MKENT(exists, 2, 0, do_env_exists, "", ""),
> +#endif
> };
>
> #if defined(CONFIG_NEEDS_MANUAL_RELOC)
> @@ -1136,6 +1156,9 @@ static char env_help_text[] =
> #if defined(CONFIG_CMD_EDITENV)
> "env edit name - edit environment variable\n"
> #endif
> +#if defined(CONFIG_CMD_ENV_EXISTS)
> + "env exists name - tests for existence of variable\n"
> +#endif
> #if defined(CONFIG_CMD_EXPORTENV)
> "env export [-t | -b | -c] [-s size] addr [var ...] - export environment\n"
> #endif
>

--
Jim Chargin
AJA Video Systems jimc at aja.com
(530) 271-3334 http://www.aja.com