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 <[email protected]>
---
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 [email protected]
(530) 271-3334 http://www.aja.com
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