posix: shell: add an environment variable shell command

This service is used to get, set, and unset system
environment variables.

Note: shell parameter expansion is not supported
at this time.

Signed-off-by: Christopher Friedt <cfriedt@meta.com>

lib/posix/shell/CMakeLists.txt

@@ -3,3 +3,4 @@
 
 zephyr_library_sources_ifdef(CONFIG_POSIX_SHELL posix_shell.c)
 zephyr_library_sources_ifdef(CONFIG_POSIX_UNAME_SHELL uname.c)
+zephyr_library_sources_ifdef(CONFIG_POSIX_ENV_SHELL env.c)

lib/posix/shell/Kconfig

@@ -10,6 +10,7 @@ config POSIX_SHELL
 	help
 	  Compile the parent `posix` shell command.
 
+rsource "Kconfig.env"
 rsource "Kconfig.uname"
 
 endif # SHELL

lib/posix/shell/Kconfig.env

@@ -0,0 +1,9 @@
+# Copyright (c) 2024 Meta
+# SPDX-License-Identifier: Apache-2.0
+
+config POSIX_ENV_SHELL
+	bool "Support for shell"
+	select POSIX_ENV
+	select POSIX_SHELL
+	help
+	  This shell provides access to system environment variables.

lib/posix/shell/env.c

@@ -0,0 +1,130 @@
+/*
+ * Copyright (c) 2023, Meta
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "posix_shell.h"
+
+#include <ctype.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <zephyr/shell/shell.h>
+
+#define HELP_ENV_GET   "[NAME]"
+#define HELP_ENV_SET   "NAME VALUE | NAME=VALUE"
+#define HELP_ENV_UNSET "NAME.."
+
+static int cmd_env_get(const struct shell *sh, size_t argc, char **argv)
+{
+	const char *name;
+	const char *value;
+
+	switch (argc) {
+	case 1: {
+		extern char **environ;
+		/* list all environment variables */
+		if (environ != NULL) {
+			for (char **envp = environ; *envp != NULL; ++envp) {
+				shell_print(sh, "%s", *envp);
+			}
+		}
+	} break;
+	case 2:
+		/* list a specific environment variable */
+		name = argv[1];
+		value = getenv(name);
+		if (value != NULL) {
+			shell_print(sh, "%s", value);
+		}
+		break;
+	default:
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+static bool is_shell_env_name(const char *name)
+{
+	char c;
+
+	if (name == NULL || name[0] == '\0') {
+		return false;
+	}
+
+	for (size_t i = 0, N = strlen(name); i < N; ++i) {
+		c = name[i];
+
+		if (c == '_') {
+			continue;
+		}
+
+		if (isalpha(c)) {
+			continue;
+		}
+
+		if (i > 0 && isdigit(c)) {
+			continue;
+		}
+
+		return false;
+	}
+
+	return true;
+}
+
+static int cmd_env_set(const struct shell *sh, size_t argc, char **argv)
+{
+	int ret;
+	char *value;
+	const char *name;
+
+	switch (argc) {
+	case 2:
+		name = argv[1];
+		value = strchr(argv[1], '=');
+		if (value != NULL) {
+			*value = '\0';
+			++value;
+		}
+		break;
+	case 3:
+		name = argv[1];
+		value = argv[2];
+		break;
+	default:
+		return EXIT_FAILURE;
+	}
+
+	/* silently drop "poorly conditioned" environment variables */
+	if (!is_shell_env_name(name)) {
+		shell_print(sh, "bad name");
+		return EXIT_SUCCESS;
+	}
+
+	ret = setenv(name, value, 1);
+	if (ret == -1) {
+		return EXIT_FAILURE;
+	}
+
+	return EXIT_SUCCESS;
+}
+
+static int cmd_env_unset(const struct shell *sh, size_t argc, char **argv)
+{
+	for (--argc, ++argv; argc > 0; --argc, ++argv) {
+		(void)unsetenv(argv[0]);
+	}
+
+	return EXIT_SUCCESS;
+}
+
+SHELL_STATIC_SUBCMD_SET_CREATE(sub_env, SHELL_CMD(set, NULL, HELP_ENV_SET, cmd_env_set),
+			       SHELL_CMD(get, NULL, HELP_ENV_GET, cmd_env_get),
+			       SHELL_CMD(unset, NULL, HELP_ENV_UNSET, cmd_env_unset),
+			       SHELL_SUBCMD_SET_END /* Array terminated. */
+);
+
+POSIX_CMD_ADD(env, &sub_env, "Print system information", NULL, 1, 255);