diff --git a/src/main.c b/src/main.c
index 1e50d3a..9dcb087 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4,30 +4,82 @@
 #include "obj.h"
 #include "render.h"
 #include "shaders.h"
+#include "str.h"
 #include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
 #include <time.h>
 
 #define IMAGE_DIMENSION 1200
-#define RESOURCE(NAME) "resources/" NAME
 
 enum {
   TINY_EXIT_SUCCESS,
+  TINY_EXIT_MISSING_ARGS,
+  TINY_EXIT_OBJ_NOT_EXIST,
   TINY_EXIT_ARENA_INIT_FAILED,
   TINY_EXIT_RENDER_INIT_FAILED,
   TINY_EXIT_MODEL_LOAD_FAILED,
 };
 
-int tinyrenderer(void);
+typedef struct tiny_args TinyArgs;
+struct tiny_args {
+  Str8 obj;
+  Str8 diffuse;
+  Str8 nm_tangent;
+};
 
-int main(void) { return tinyrenderer(); }
+internal TinyArgs parse_args(Arena *arena, int argc, char *argv[]);
+internal i32 tinyrenderer(Arena *arena, TinyArgs args);
+internal bool file_exists(const Str8 *path);
 
-int tinyrenderer(void) {
+i32 main(int argc, char *argv[]) {
   Arena *arena = NULL;
   if (!wapp_mem_arena_init(&arena, GB(10))) {
     return TINY_EXIT_ARENA_INIT_FAILED;
   }
 
+  TinyArgs args = parse_args(arena, argc, argv);
+
+  i32 output = tinyrenderer(arena, args);
+
+  wapp_mem_arena_destroy(&arena);
+
+  return output;
+}
+
+internal TinyArgs parse_args(Arena *arena, int argc, char *argv[]) {
+  if (argc < 2) {
+    exit(TINY_EXIT_MISSING_ARGS);
+  }
+
+  TinyArgs args = {
+      .obj = str8_lit(argv[1]),
+  };
+
+  if (!file_exists(&args.obj)) {
+    exit(TINY_EXIT_OBJ_NOT_EXIST);
+  }
+
+  const Str8 basename = str8_substr(&args.obj, 0, args.obj.length - 4);
+
+  args.diffuse = str8_copy(arena, &basename);
+  str8_concat(arena, &args.diffuse, "_diffuse.pnm");
+  if (!file_exists(&args.diffuse)) {
+    args.diffuse = (Str8){0};
+  }
+
+  args.nm_tangent = str8_copy(arena, &basename);
+  str8_concat(arena, &args.nm_tangent, "_nm_tangent.pnm");
+  if (!file_exists(&args.nm_tangent)) {
+    args.nm_tangent = (Str8){0};
+  }
+
+  return args;
+}
+
+internal i32 tinyrenderer(Arena *arena, TinyArgs args) {
   Colour bg = {.r = 42, .g = 45, .b = 52, .a = 255};
   Colour main_colour = {.r = 14, .g = 156, .b = 208, .a = 255};
   Render render;
@@ -35,8 +87,9 @@ int tinyrenderer(void) {
     return TINY_EXIT_RENDER_INIT_FAILED;
   }
 
-  Model obj = load_obj_file(arena, RESOURCE("head.obj"), RESOURCE("head.pnm"),
-                            RESOURCE("head_nm_tangent.pnm"));
+  Model obj = load_obj_file(
+      arena, args.obj.str, args.diffuse.length > 0 ? args.diffuse.str : NULL,
+      args.nm_tangent.length > 0 ? args.nm_tangent.str : NULL);
   if (IS_INVALID_MODEL(obj)) {
     return TINY_EXIT_MODEL_LOAD_FAILED;
   }
@@ -48,7 +101,10 @@ int tinyrenderer(void) {
                main_colour);
   save_image(&(render.img), "result.pam");
 
-  wapp_mem_arena_destroy(&arena);
-
   return TINY_EXIT_SUCCESS;
 }
+
+internal bool file_exists(const Str8 *path) {
+  struct stat st;
+  return stat(path->str, &st) == 0;
+}
diff --git a/src/str/str.c b/src/str/str.c
new file mode 100644
index 0000000..d82e77d
--- /dev/null
+++ b/src/str/str.c
@@ -0,0 +1,98 @@
+#include "str.h"
+#include "aliases.h"
+#include "mem_arena.h"
+#include <stddef.h>
+#include <string.h>
+
+#define CAPACITY_SCALAR 8
+
+internal Arena *get_temp_arena(void);
+internal void destroy_temp_arena(Arena *arena);
+
+Str8 str8(Arena *arena, char *str) {
+  if (!str) {
+    return (Str8){0};
+  }
+
+  u64 length = strlen(str);
+  Str8 output = {
+      .str = str,
+      .length = length,
+      .capacity = length,
+  };
+
+  if (arena) {
+    output.capacity *= CAPACITY_SCALAR;
+
+    output.str = wapp_mem_arena_alloc(arena, output.capacity);
+    if (!output.str) {
+      return (Str8){0};
+    }
+
+    strncpy(output.str, str, output.length);
+  }
+
+  return output;
+}
+
+Str8 str8_copy(Arena *arena, const Str8 *str) {
+  if (!arena) {
+    return str8_lit(str->str);
+  }
+
+  char *tmp = wapp_mem_arena_alloc(arena, str->capacity);
+  if (!tmp) {
+    return str8_lit(str->str);
+  }
+
+  strncpy(tmp, str->str, str->length);
+
+  return (Str8){
+      .str = tmp,
+      .length = str->length,
+      .capacity = str->capacity,
+  };
+}
+
+i32 str8_concat(Arena *arena, Str8 *dst, char *src) {
+  if (!src || !dst) {
+    return STR_OP_FAILED;
+  }
+
+  u64 src_length = strlen(src);
+  if (src_length + dst->length > dst->capacity) {
+    if (!arena) {
+      return STR_OP_FAILED;
+    }
+
+    u64 capacity = dst->capacity * CAPACITY_SCALAR + src_length;
+    char *str = wapp_mem_arena_alloc(arena, capacity);
+    if (!str) {
+      return STR_OP_FAILED;
+    }
+
+    strncpy(str, dst->str, dst->length);
+    strncpy(str + dst->length, src, src_length);
+
+    dst->str = str;
+    dst->length = dst->length + src_length;
+    dst->capacity = capacity;
+
+    return STR_OP_SUCEEDED;
+  }
+
+  strncpy(dst->str + dst->length, src, src_length);
+  return STR_OP_SUCEEDED;
+}
+
+const Str8 str8_substr(const Str8 *str, u64 start, u64 count) {
+  if (start > str->length || start + count > str->length) {
+    return (Str8){0};
+  }
+
+  return (Str8){
+      .str = str->str + start,
+      .length = count,
+      .capacity = count,
+  };
+}
diff --git a/src/str/str.h b/src/str/str.h
new file mode 100644
index 0000000..771bdc2
--- /dev/null
+++ b/src/str/str.h
@@ -0,0 +1,26 @@
+#ifndef STR_H
+#define STR_H
+
+#include "aliases.h"
+#include "mem_arena.h"
+
+enum {
+  STR_OP_SUCEEDED,
+  STR_OP_FAILED,
+};
+
+typedef struct str8 Str8;
+struct str8 {
+  char *str;
+  u64 length;
+  u64 capacity;
+};
+
+#define str8_lit(STR) (str8(NULL, STR))
+
+Str8 str8(Arena *arena, char *str);
+Str8 str8_copy(Arena *arena, const Str8 *str);
+i32 str8_concat(Arena *arena, Str8 *dst, char *src);
+const Str8 str8_substr(const Str8 *str, u64 start, u64 count);
+
+#endif // !STR_H