Correctly structured project & implemented required functions

src/main.c

@@ -0,0 +1,52 @@
+#include "headers/nstdo.h"
+extern long sys_read(int fd, void *buf, size_t cnt);
+extern long sys_write(int fd, const void *buf, size_t cnt);
+extern long sys_fork(void);
+extern long sys_execve(const char *filename, char *const argv[], char *const envp[]);
+extern long sys_wait4(int pid, int *wstatus, int options, void *rusage);
+extern void sys_exit(int status);
+
+static int streq(const char *a, const char *b) {
+    while (*a && *b) {
+        if (*a != *b) return 0;
+        a++; b++;
+    }
+    return *a == *b;
+}
+
+static long str_len(const char *s) {
+    long len = 0;
+    while (s[len]) len++;
+    return len;
+}
+
+int main(int argc, char *argv[], char *envp[]) {
+    (void)argc; (void)argv;
+    const char prompt[] = "$ ";
+    char buf[512];
+    while (1) {
+        sys_write(1, prompt, sizeof(prompt)-1);
+        long n = sys_read(0, buf, sizeof(buf)-1);
+        if (n <= 0) break;
+        buf[n-1] = '\0';
+        if (streq(buf, "help")) {
+            const char *h1 = "  help  - display this help message\n";
+            const char *h2 = "  exit  - exit the shell\n";
+            sys_write(1, h1, str_len(h1));
+            sys_write(1, h2, str_len(h2));
+            continue;
+        }
+        if (streq(buf, "exit")) {
+            break;
+        }
+        char *args[] = { buf, NULL };
+        long pid = sys_fork();
+        if (pid == 0) {
+            sys_execve(buf, args, envp);
+            sys_exit(1);
+        } else {
+            sys_wait4(pid, 0, 0, 0);
+        }
+    }
+    return 0;
+}