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

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.

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
$

Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>
---
 README              |  1 +
 common/cmd_nvedit.c | 23 +++++++++++++++++++++++
 2 files changed, 24 insertions(+)

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
>

On Wed, Oct 23, 2013 at 06:55:02AM -0700, James Chargin wrote:
> I have, more recently, been using scripting of the form
> 
> 	if test "X" != "X${var}"; then
> 		echo defined
> 	else
> 		echo undefined
> 	fi

Thanks for the feedback.

I was attempting to do something like that originally but was hitting
problems related to the expansion which I'm still tracking down:

   WRONG:
   $ set var
   $ test "x${var}" = "x" && echo undefined
   undefined
   $ set var 1
   $ test "x${var}" = "x" && echo undefined
   $ set var "1; 2; 3"
   $ test "x${var}" = "x" && echo undefined
>> undefined

It DOES seem to work a lot better with != as you mentioned above
though...

   RIGHT:
   $ set var
   $ test "x${var}" != "x" && echo defined
   $ set var 1
   $ test "x${var}" != "x" && echo defined
   defined
   $ set var "1; 2; 3"
   $ test "x${var}" != "x" && echo defined
   defined

- Andy

On Tue, Oct 22, 2013 at 07:07:34PM -0500, 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.
> 
> 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
> $
> 
> Signed-off-by: Andrew Ruder <andrew.ruder@elecsyscorp.com>

Applied to u-boot/master, thanks!