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

[Andrew Ruder <andrew.ruder@elecsyscorp.com>]

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(+)

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
-- 
1.8.4.rc3