apps: Add ls

apps/CMakeLists.txt

@@ -11,3 +11,4 @@ luna_app(cat.c cat)
 luna_app(edit.c edit)
 luna_app(sh.c sh)
 luna_app(date.c date)
+luna_app(ls.c ls)

apps/ls.c

@@ -0,0 +1,32 @@
+#include <dirent.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+    const char* pathname;
+    if (argc == 1) pathname = "/";
+    else
+        pathname = argv[1];
+
+    DIR* dp = opendir(pathname);
+    if (!dp)
+    {
+        perror("opendir");
+        return 1;
+    }
+
+    int first_ent = 1;
+    do {
+        struct dirent* ent = readdir(dp);
+        if (!ent) break;
+        printf(first_ent ? "%s" : " %s", ent->d_name);
+        first_ent = 0;
+    } while (1);
+
+    putchar('\n');
+
+    closedir(dp);
+    return 0;
+}