Update MentOs code to the latest development version.

programs/tests/t_exec.c

@@ -0,0 +1,65 @@
+///                MentOS, The Mentoring Operating system project
+/// @file t_exec.c
+/// @brief
+/// @copyright (c) 2014-2021 This file is distributed under the MIT License.
+/// See LICENSE.md for details.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/unistd.h>
+#include <sys/wait.h>
+#include <string.h>
+
+static inline void __print_usage(int argc, char *argv[])
+{
+    if (argc > 0) {
+        printf("%s: Usage: %s <exec_type>\n", argv[0], argv[0]);
+        printf("exec_type: execl, execlp, execle, execlpe, execv, execvp, execve, execvpe\n");
+    }
+}
+
+int main(int argc, char *argv[])
+{
+    int status;
+    if (argc != 2) {
+        __print_usage(argc, argv);
+        return 1;
+    }
+
+    if (setenv("ENV_VAR", "pwd0", 0) == -1) {
+        printf("Failed to set env: `ENV_VAR`\n");
+        return 1;
+    }
+
+    char *file        = "echo";
+    char *path        = "/bin/echo";
+    char *exec_argv[] = { "echo", "ENV_VAR: ${ENV_VAR}", NULL };
+    char *exec_envp[] = { "PATH=/bin", "ENV_VAR=pwd1", NULL };
+
+    if (fork() == 0) {
+        if (strcmp(argv[1], "execl") == 0) {
+            execl(path, "echo", "ENV_VAR: ${ENV_VAR}", NULL);
+        } else if (strcmp(argv[1], "execlp") == 0) {
+            execlp(file, "echo", "ENV_VAR: ${ENV_VAR}", NULL);
+        } else if (strcmp(argv[1], "execle") == 0) {
+            execle(path, "echo", "ENV_VAR: ${ENV_VAR}", exec_envp, NULL);
+        } else if (strcmp(argv[1], "execlpe") == 0) {
+            execlpe(file, "echo", "ENV_VAR: ${ENV_VAR}", exec_envp, NULL);
+        } else if (strcmp(argv[1], "execv") == 0) {
+            execv(path, exec_argv);
+        } else if (strcmp(argv[1], "execvp") == 0) {
+            execvp(file, exec_argv);
+        } else if (strcmp(argv[1], "execve") == 0) {
+            execve(path, exec_argv, exec_envp);
+        } else if (strcmp(argv[1], "execvpe") == 0) {
+            execvpe(file, exec_argv, exec_envp);
+        } else {
+            __print_usage(argc, argv);
+            return 1;
+        }
+        printf("Exec failed.\n");
+        return 1;
+    }
+    wait(&status);
+    return 0;
+}