diff --git a/core.cpp b/core.cpp
index 3e2f774..c08b51b 100644
--- a/core.cpp
+++ b/core.cpp
@@ -1,11 +1,20 @@
+#include "os.cpp"
 #include <math.h>
 #include <string.h>
-#include <unistd.h>
 #include "core.h"
-#include "os.cpp"
 #define STB_SPRINTF_IMPLEMENTATION
 #include "vendor/stb_sprintf.h"
 
+void *pushSizeFill(Arena *arena, size_t bytes, byte fill) {
+    if (arena->capacity - arena->head >= bytes) {
+        void *ptr = (char *)arena->memory + arena->head;
+        arena->head += bytes;
+        memset(ptr, fill, bytes);
+        return ptr;
+    }
+    return 0;
+}
+
 void *pushSize(Arena *arena, size_t bytes) {
     if (arena->capacity - arena->head >= bytes) {
         void *ptr = (char *)arena->memory + arena->head;
@@ -112,6 +121,18 @@ const char *cstring(Arena *arena, string str) {
     return arr;
 }
 
+bool strStartsWith(string str, string testStr) {
+    if (str.length < testStr.length) {
+        return false;
+    }
+    for (size_t i = 0; i < testStr.length; i++) {
+        if (str.str[i] != testStr.str[i]) {
+            return false;
+        }
+    }
+    return true;
+}
+
 bool strEql(string s1, string s2) {
     if (s1.length != s2.length) {
         return false;
@@ -307,81 +328,14 @@ real32 parsePositiveReal32(string str, size_t *lengthPointer) {
     return result;
 }
 
-string readEntireFile(Arena *arena, string filename) {
-#if OS_WINDOWS
-    string result = {0};
-    HANDLE fileHandle = CreateFileA(cstring(arena, filename), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, NULL, NULL);
-    if (fileHandle != INVALID_HANDLE_VALUE) {
-        LARGE_INTEGER fileSize;
-        if (GetFileSizeEx(fileHandle, &fileSize)) {
-            string readfile = PushString(arena, (size_t)fileSize.QuadPart);
-            if (readfile.str) {
-                DWORD bytesRead;
-                if (ReadFile(fileHandle, readfile.str, (DWORD)fileSize.QuadPart, &bytesRead, NULL) && (fileSize.QuadPart == bytesRead)) {
-                    result = readfile;
-                }
-            }
-        }
-        CloseHandle(fileHandle);
-    }
-    return result;
-#elif OS_LINUX
-    FILE *input = fopen((char *)filename.str, "r");
-    struct stat st;
-    stat((char *)filename.str, &st);
-    size_t fsize = st.st_size;
-    string readBuffer = PushString(arena, fsize);
-    fread(readBuffer.str, sizeof(byte), readBuffer.length, input);
-    fclose(input);
-    return readBuffer;
-#endif
-}
-
-bool writeEntireFile(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
-    bool result = false;
-#if OS_WINDOWS
-    HANDLE fileHandle = CreateFileA(cstring(arena, filename), GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS, NULL, NULL);
-    if (fileHandle != INVALID_HANDLE_VALUE) {
-        DWORD bytesWritten;
-        if (WriteFile(fileHandle, contents, (DWORD)contentsLength, &bytesWritten, NULL)) {
-            // file written successfully
-            result = bytesWritten == contentsLength;
-        }  
-        CloseHandle(fileHandle);
-    }  
-#elif OS_LINUX
-    Assert(false);
-#endif
-    return result;
-}
-
-bool fileAppend(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
-    bool result = false;
-#if OS_WINDOWS
-    HANDLE fileHandle = CreateFileA(cstring(arena, filename), FILE_APPEND_DATA | FILE_GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
-    if (fileHandle != INVALID_HANDLE_VALUE) {
-        DWORD bytesWritten;
-        DWORD position = SetFilePointer(fileHandle, 0, NULL, FILE_END);
-        if (WriteFile(fileHandle, contents, (DWORD)contentsLength, &bytesWritten, NULL)) {
-            // file written successfully
-            result = bytesWritten == contentsLength;
-        }
-        CloseHandle(fileHandle);
-    }
-#elif OS_LINUX
-    Assert(false);
-#endif
-    return result;
-}
-
 list<string> getArgs(Arena *arena, int argc, char **argv) {
-    list<string> args = PushList(arena, string, (size_t)argc);
+    list<string> args = PushList(arena, string, (size_t)argc - 1);
     for (int i = 1; i < argc; i++) {
         appendList(&args, strFromCString(arena, argv[i]));
     }
     return args;
 }
-
+ 
 UnixTimestamp getSystemUnixTime() {
     time_t now;
     time(&now);
@@ -389,8 +343,9 @@ UnixTimestamp getSystemUnixTime() {
 }
 
 Timestamp timestampFromUnixTime(UnixTimestamp *unixTimestamp) {
-    tm *timestamp = gmtime((time_t *)&time);
-    return *timestamp;
+    tm timestamp = {0};
+    gmtime_r((time_t *)unixTimestamp, &timestamp);
+    return timestamp;
 }
 
 string formatTimeHms(Arena *arena, UnixTimestamp time) {
@@ -423,65 +378,24 @@ string formatTimeYmd(Arena *arena, Timestamp *time) {
     return buf;
 }
 
-function void __core_log(LogTarget target, const char *fmt, va_list argList) {
-    Scratch scratch = scratchStart(0, 0);
-    string result = strPrintfv(scratch.arena, fmt, argList);
-#if OS_WINDOWS
-    DWORD done;
-    HANDLE stdHandle;
-    switch (target) {
-        case LogTarget_stdin: 
-            stdHandle = GetStdHandle(STD_INPUT_HANDLE);
-            break;
-        case LogTarget_stdout: 
-            stdHandle = GetStdHandle(STD_ERROR_HANDLE);
-            break;
-        case LogTarget_stderr: 
-            stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
-            break;
-        default:
-            stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
-            break;
-    }
-    WriteFile(stdHandle, result.str, (DWORD)result.length, &done, 0);
-#elif OS_LINUX
-    // TODO(djledda): finish implementation without cstdlib
-    switch (target) {
-        case LogTarget_stdin: 
-            write(0, (const void *)result.str, result.length);
-            break;
-        case LogTarget_stderr: 
-            fflush(stderr);
-            write(2, (const void *)result.str, result.length);
-            break;
-        case LogTarget_stdout: 
-        default:
-            fflush(stdout);
-            write(1, (const void *)result.str, result.length);
-            break;
-    }
-#endif
-    scratchEnd(scratch);
-}
-
 void logErr(const char *fmt, ...) {
     va_list argList;
     va_start(argList, fmt);
-    __core_log(LogTarget_stdout, fmt, argList);
+    os_log(LogTarget_stdout, fmt, argList);
     va_end(argList);
 }
 
 function void logStdout(const char *fmt, ...) {
     va_list argList;
     va_start(argList, fmt);
-    __core_log(LogTarget_stdout, fmt, argList);
+    os_log(LogTarget_stdout, fmt, argList);
     va_end(argList);
 }
 
 void log(const char *fmt, ...) {
     va_list argList;
     va_start(argList, fmt);
-    __core_log(LogTarget_stdout, fmt, argList);
+    os_log(LogTarget_stdout, fmt, argList);
     va_end(argList);
 }
 
diff --git a/core.h b/core.h
index 5e796e7..2889d13 100644
--- a/core.h
+++ b/core.h
@@ -57,6 +57,7 @@ struct Scratch {
 };
 
 void *pushSize(Arena *arena, size_t bytes);
+void *pushSizeFill(Arena *arena, size_t bytes, byte fill);
 Arena *arenaAlloc(size_t capacity);
 void arenaFree(Arena *arena);
 void arenaFreeFrom(Arena *arena, size_t pos);
@@ -68,7 +69,9 @@ Scratch scratchStart(Arena **conflicts, size_t conflictCount);
 void scratchEnd(Scratch scratch); 
 
 #define PushArray(arena, type, size) (type *)pushSize(arena, sizeof(type) * (size))
+#define PushArrayZero(arena, type, size) (type *)pushSizeFill(arena, sizeof(type) * (size), 0)
 #define PushStruct(arena, type) (type *)pushSize(arena, sizeof(type))
+#define PushStructZero(arena, type) (type *)pushSizeFill(arena, sizeof(type), 0)
 
 // ### Vectors ###
 template <typename T>
@@ -134,7 +137,9 @@ struct list {
 };
 
 #define PushList(arena, type, size) (list<type>{ PushArray(arena, type, size), size, 0 })
+#define PushListZero(arena, type, size) (list<type>{ PushArrayZero(arena, type, size), size, 0 })
 #define PushFullList(arena, type, size) (list<type>{ PushArray(arena, type, size), size, size })
+#define PushFullListZero(arena, type, size) (list<type>{ PushArrayZero(arena, type, size), size, size })
 
 template <typename T> T *appendList(list<T> *list, T element); 
 template <typename T> void zeroList(list<T> *list); 
@@ -151,6 +156,7 @@ struct string {
 
 #define strlit(lit) (string{(char *)(lit), sizeof(lit) - 1})
 #define PushString(arena, length) (string{ (char *)pushSize(arena, length), (length) })
+#define PushStringFill(arena, length, characterByte) (string{ (char *)pushSizeFill(arena, length, characterByte), (length) })
 string operator""_s(const char *cstrLiteral, size_t length);
 
 // C Strings
@@ -160,6 +166,7 @@ size_t calcStringLen(const char *str);
 string strFromCString(Arena *arena, const char *str); 
 
 bool strEql(string s1, string s2); 
+bool strStartsWith(string str, string testStr);
 bool stringContains(string str, char c); 
 
 string strReverse(Arena *arena, string str); 
@@ -174,11 +181,6 @@ real32 parsePositiveReal32(Arena *arena, string str, size_t *lengthPointer);
 
 inline function bool isNumeric(char c); 
 
-// ### File IO ###
-string readEntireFile(Arena *arena, string filename); 
-bool writeEntireFile(Arena *arena, string filename, const byte *contents, size_t contentsLength); 
-bool fileAppend(Arena *arena, string filename, const byte *contents, size_t contentsLength); 
-
 // ### Cmdline ###
 list<string> getArgs(Arena *arena, int argc, char **argv); 
 
diff --git a/os.h b/os.h
index 44aac28..07b654e 100644
--- a/os.h
+++ b/os.h
@@ -9,4 +9,12 @@ void os_reserve(void *ptr);
 void os_decommit(void *ptr);
 void os_free(void *ptr, size_t freeSize);
 
+// ### File IO ###
+string os_readEntireFile(Arena *arena, string filename); 
+bool os_writeEntireFile(Arena *arena, string filename, const byte *contents, size_t contentsLength); 
+bool os_fileAppend(Arena *arena, string filename, const byte *contents, size_t contentsLength); 
+
+// ### Standard IO ###
+void os_log(LogTarget target, const char *fmt, va_list argList);
+
 #endif
diff --git a/os_linux.cpp b/os_linux.cpp
index 122a4bb..69817d7 100644
--- a/os_linux.cpp
+++ b/os_linux.cpp
@@ -5,6 +5,7 @@
 
 #include <sys/mman.h>
 #include <sys/stat.h>
+#include <unistd.h>
 
 void *os_alloc(size_t capacity) {
     return mmap(0, capacity, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@@ -21,4 +22,77 @@ void os_free(void *ptr, size_t size) {
     Assert(err != -1);
 }
 
+string os_readEntireFile(Arena *arena, string filename) {
+    Scratch temp = scratchStart(&arena, 1);
+
+    FILE *input = fopen(cstring(temp.arena, filename), "r");
+    string readBuffer;
+    if (input) {
+        struct stat st;
+        stat((char *)filename.str, &st);
+        size_t fsize = st.st_size;
+        readBuffer = PushString(arena, fsize);
+        fread(readBuffer.str, sizeof(byte), readBuffer.length, input);
+        fclose(input);
+    } else {
+        readBuffer = PushString(arena, 0);
+    }
+
+    scratchEnd(temp);
+    return readBuffer;
+}
+
+bool os_writeEntireFile(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
+    Scratch temp = scratchStart(&arena, 1);
+
+    bool result = false;
+    FILE *output = fopen(cstring(temp.arena, filename), "w");
+    if (output) {
+        fwrite(contents, sizeof(byte), contentsLength, output);
+        fclose(output);
+        result = true;
+    }
+
+    scratchEnd(temp);
+    return result;
+}
+
+bool os_fileAppend(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
+    Scratch temp = scratchStart(&arena, 1);
+
+    bool result = false;
+    FILE *output = fopen(cstring(temp.arena, filename), "a");
+    if (output) {
+        fwrite(contents, sizeof(byte), contentsLength, output);
+        fclose(output);
+        result = true;
+    }
+
+    scratchEnd(temp);
+    return result;
+}
+
+void os_log(LogTarget target, const char *fmt, va_list argList) {
+    Scratch temp = scratchStart(0, 0);
+
+    string result = strPrintfv(temp.arena, fmt, argList);
+    // TODO(djledda): finish implementation without cstdlib
+    switch (target) {
+        case LogTarget_stdin: 
+            write(0, (const void *)result.str, result.length);
+            break;
+        case LogTarget_stderr: 
+            fflush(stderr);
+            write(2, (const void *)result.str, result.length);
+            break;
+        case LogTarget_stdout: 
+        default:
+            fflush(stdout);
+            write(1, (const void *)result.str, result.length);
+            break;
+    }
+
+    scratchEnd(temp);
+}
+
 #endif
diff --git a/os_win32.cpp b/os_win32.cpp
index 01eb4ec..70ba555 100644
--- a/os_win32.cpp
+++ b/os_win32.cpp
@@ -1,8 +1,8 @@
 #ifndef OS_IMPL_WIN32_CPP
 #define OS_IMPL_WIN32_CPP
 
-#include "os.h"
 #include "Windows.h" 
+#include "os.h"
 
 void *os_alloc(size_t commitSize) {
     return VirtualAlloc(NULL, commitSize, MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
@@ -18,4 +18,75 @@ void os_free(void *ptr, size_t size) {
     VirtualFree(ptr, NULL, MEM_RELEASE);
 }
 
+string os_readEntireFile(Arena *arena, string filename) {
+    string result = {0};
+    HANDLE fileHandle = CreateFileA(cstring(arena, filename), GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, NULL, NULL);
+    if (fileHandle != INVALID_HANDLE_VALUE) {
+        LARGE_INTEGER fileSize;
+        if (GetFileSizeEx(fileHandle, &fileSize)) {
+            string readfile = PushString(arena, (size_t)fileSize.QuadPart);
+            if (readfile.str) {
+                DWORD bytesRead;
+                if (ReadFile(fileHandle, readfile.str, (DWORD)fileSize.QuadPart, &bytesRead, NULL) && (fileSize.QuadPart == bytesRead)) {
+                    result = readfile;
+                }
+            }
+        }
+        CloseHandle(fileHandle);
+    }
+    return result;
+}
+
+bool os_writeEntireFile(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
+    bool result = false;
+    HANDLE fileHandle = CreateFileA(cstring(arena, filename), GENERIC_WRITE, FILE_SHARE_READ, NULL, CREATE_ALWAYS, NULL, NULL);
+    if (fileHandle != INVALID_HANDLE_VALUE) {
+        DWORD bytesWritten;
+        if (WriteFile(fileHandle, contents, (DWORD)contentsLength, &bytesWritten, NULL)) {
+            // file written successfully
+            result = bytesWritten == contentsLength;
+        }  
+        CloseHandle(fileHandle);
+    }  
+    return result;
+}
+
+bool os_fileAppend(Arena *arena, string filename, const byte *contents, size_t contentsLength) {
+    bool result = false;
+    HANDLE fileHandle = CreateFileA(cstring(arena, filename), FILE_APPEND_DATA | FILE_GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
+    if (fileHandle != INVALID_HANDLE_VALUE) {
+        DWORD bytesWritten;
+        DWORD position = SetFilePointer(fileHandle, 0, NULL, FILE_END);
+        if (WriteFile(fileHandle, contents, (DWORD)contentsLength, &bytesWritten, NULL)) {
+            // file written successfully
+            result = bytesWritten == contentsLength;
+        }
+        CloseHandle(fileHandle);
+    }
+    return result;
+}
+
+function void os_log(LogTarget target, const char *fmt, va_list argList) {
+    Scratch scratch = scratchStart(0, 0);
+    string result = strPrintfv(scratch.arena, fmt, argList);
+    DWORD done;
+    HANDLE stdHandle;
+    switch (target) {
+        case LogTarget_stdin: 
+            stdHandle = GetStdHandle(STD_INPUT_HANDLE);
+            break;
+        case LogTarget_stdout: 
+            stdHandle = GetStdHandle(STD_ERROR_HANDLE);
+            break;
+        case LogTarget_stderr: 
+            stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
+            break;
+        default:
+            stdHandle = GetStdHandle(STD_OUTPUT_HANDLE);
+            break;
+    }
+    WriteFile(stdHandle, result.str, (DWORD)result.length, &done, 0);
+    scratchEnd(scratch);
+}
+
 #endif