diff --git a/src/libstd/c_str.rs b/src/libstd/c_str.rs
index fe332a60efa..adbd4be316c 100644
--- a/src/libstd/c_str.rs
+++ b/src/libstd/c_str.rs
@@ -79,6 +79,7 @@ use str;
 use vec::{ImmutableVector, MutableVector};
 use vec;
 use rt::global_heap::malloc_raw;
+use unstable::raw::Slice;
 
 /// The representation of a C String.
 ///
@@ -169,6 +170,7 @@ impl CString {
     }
 
     /// Converts the CString into a `&[u8]` without copying.
+    /// Includes the terminating NUL byte.
     ///
     /// # Failure
     ///
@@ -177,7 +179,21 @@ impl CString {
     pub fn as_bytes<'a>(&'a self) -> &'a [u8] {
         if self.buf.is_null() { fail!("CString is null!"); }
         unsafe {
-            cast::transmute((self.buf, self.len() + 1))
+            cast::transmute(Slice { data: self.buf, len: self.len() + 1 })
+        }
+    }
+
+    /// Converts the CString into a `&[u8]` without copying.
+    /// Does not include the terminating NUL byte.
+    ///
+    /// # Failure
+    ///
+    /// Fails if the CString is null.
+    #[inline]
+    pub fn as_bytes_no_nul<'a>(&'a self) -> &'a [u8] {
+        if self.buf.is_null() { fail!("CString is null!"); }
+        unsafe {
+            cast::transmute(Slice { data: self.buf, len: self.len() })
         }
     }
 
@@ -189,8 +205,7 @@ impl CString {
     /// Fails if the CString is null.
     #[inline]
     pub fn as_str<'a>(&'a self) -> Option<&'a str> {
-        let buf = self.as_bytes();
-        let buf = buf.slice_to(buf.len()-1); // chop off the trailing NUL
+        let buf = self.as_bytes_no_nul();
         str::from_utf8(buf)
     }
 
@@ -417,7 +432,7 @@ mod tests {
             let expected = ["zero", "one"];
             let mut it = expected.iter();
             let result = from_c_multistring(ptr as *libc::c_char, None, |c| {
-                let cbytes = c.as_bytes().slice_to(c.len());
+                let cbytes = c.as_bytes_no_nul();
                 assert_eq!(cbytes, it.next().unwrap().as_bytes());
             });
             assert_eq!(result, 2);
@@ -552,6 +567,17 @@ mod tests {
         assert_eq!(c_str.as_bytes(), bytes!("foo", 0xff, 0));
     }
 
+    #[test]
+    fn test_as_bytes_no_nul() {
+        let c_str = "hello".to_c_str();
+        assert_eq!(c_str.as_bytes_no_nul(), bytes!("hello"));
+        let c_str = "".to_c_str();
+        let exp: &[u8] = [];
+        assert_eq!(c_str.as_bytes_no_nul(), exp);
+        let c_str = bytes!("foo", 0xff).to_c_str();
+        assert_eq!(c_str.as_bytes_no_nul(), bytes!("foo", 0xff));
+    }
+
     #[test]
     #[should_fail]
     fn test_as_bytes_fail() {
@@ -559,6 +585,13 @@ mod tests {
         c_str.as_bytes();
     }
 
+    #[test]
+    #[should_fail]
+    fn test_as_bytes_no_nul_fail() {
+        let c_str = unsafe { CString::new(ptr::null(), false) };
+        c_str.as_bytes_no_nul();
+    }
+
     #[test]
     fn test_as_str() {
         let c_str = "hello".to_c_str();
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 78cae296457..20d1ae2f3e2 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -53,6 +53,8 @@ use ptr::RawPtr;
 
 #[cfg(unix)]
 use c_str::ToCStr;
+#[cfg(windows)]
+use str::OwnedStr;
 
 /// Delegates to the libc close() function, returning the same return value.
 pub fn close(fd: int) -> int {
@@ -158,10 +160,23 @@ fn with_env_lock<T>(f: || -> T) -> T {
 
 /// Returns a vector of (variable, value) pairs for all the environment
 /// variables of the current process.
+///
+/// Invalid UTF-8 bytes are replaced with \uFFFD. See `str::from_utf8_lossy()`
+/// for details.
 pub fn env() -> ~[(~str,~str)] {
+    env_as_bytes().move_iter().map(|(k,v)| {
+        let k = str::from_utf8_lossy(k).into_owned();
+        let v = str::from_utf8_lossy(v).into_owned();
+        (k,v)
+    }).collect()
+}
+
+/// Returns a vector of (variable, value) byte-vector pairs for all the
+/// environment variables of the current process.
+pub fn env_as_bytes() -> ~[(~[u8],~[u8])] {
     unsafe {
         #[cfg(windows)]
-        unsafe fn get_env_pairs() -> ~[~str] {
+        unsafe fn get_env_pairs() -> ~[~[u8]] {
             use c_str;
             use str::StrSlice;
 
@@ -176,13 +191,15 @@ pub fn env() -> ~[(~str,~str)] {
             }
             let mut result = ~[];
             c_str::from_c_multistring(ch as *c_char, None, |cstr| {
-                result.push(cstr.as_str().unwrap().to_owned());
+                result.push(cstr.as_bytes_no_nul().to_owned());
             });
             FreeEnvironmentStringsA(ch);
             result
         }
         #[cfg(unix)]
-        unsafe fn get_env_pairs() -> ~[~str] {
+        unsafe fn get_env_pairs() -> ~[~[u8]] {
+            use c_str::CString;
+
             extern {
                 fn rust_env_pairs() -> **c_char;
             }
@@ -193,20 +210,19 @@ pub fn env() -> ~[(~str,~str)] {
             }
             let mut result = ~[];
             ptr::array_each(environ, |e| {
-                let env_pair = str::raw::from_c_str(e);
-                debug!("get_env_pairs: {}", env_pair);
+                let env_pair = CString::new(e, false).as_bytes_no_nul().to_owned();
                 result.push(env_pair);
             });
             result
         }
 
-        fn env_convert(input: ~[~str]) -> ~[(~str, ~str)] {
+        fn env_convert(input: ~[~[u8]]) -> ~[(~[u8], ~[u8])] {
             let mut pairs = ~[];
             for p in input.iter() {
-                let vs: ~[&str] = p.splitn('=', 1).collect();
-                debug!("splitting: len: {}", vs.len());
-                assert_eq!(vs.len(), 2);
-                pairs.push((vs[0].to_owned(), vs[1].to_owned()));
+                let vs: ~[&[u8]] = p.splitn(1, |b| *b == '=' as u8).collect();
+                let key = vs[0].to_owned();
+                let val = (if vs.len() < 2 { ~[] } else { vs[1].to_owned() });
+                pairs.push((key, val));
             }
             pairs
         }
@@ -220,14 +236,34 @@ pub fn env() -> ~[(~str,~str)] {
 #[cfg(unix)]
 /// Fetches the environment variable `n` from the current process, returning
 /// None if the variable isn't set.
+///
+/// Any invalid UTF-8 bytes in the value are replaced by \uFFFD. See
+/// `str::from_utf8_lossy()` for details.
+///
+/// # Failure
+///
+/// Fails if `n` has any interior NULs.
 pub fn getenv(n: &str) -> Option<~str> {
+    getenv_as_bytes(n).map(|v| str::from_utf8_lossy(v).into_owned())
+}
+
+#[cfg(unix)]
+/// Fetches the environment variable `n` byte vector from the current process,
+/// returning None if the variable isn't set.
+///
+/// # Failure
+///
+/// Fails if `n` has any interior NULs.
+pub fn getenv_as_bytes(n: &str) -> Option<~[u8]> {
+    use c_str::CString;
+
     unsafe {
         with_env_lock(|| {
             let s = n.with_c_str(|buf| libc::getenv(buf));
             if s.is_null() {
                 None
             } else {
-                Some(str::raw::from_c_str(s))
+                Some(CString::new(s, false).as_bytes_no_nul().to_owned())
             }
         })
     }
@@ -249,10 +285,21 @@ pub fn getenv(n: &str) -> Option<~str> {
     }
 }
 
+#[cfg(windows)]
+/// Fetches the environment variable `n` byte vector from the current process,
+/// returning None if the variable isn't set.
+pub fn getenv_as_bytes(n: &str) -> Option<~[u8]> {
+    getenv(n).map(|s| s.into_bytes())
+}
+
 
 #[cfg(unix)]
 /// Sets the environment variable `n` to the value `v` for the currently running
 /// process
+///
+/// # Failure
+///
+/// Fails if `n` or `v` have any interior NULs.
 pub fn setenv(n: &str, v: &str) {
     unsafe {
         with_env_lock(|| {
@@ -283,6 +330,10 @@ pub fn setenv(n: &str, v: &str) {
 }
 
 /// Remove a variable from the environment entirely
+///
+/// # Failure
+///
+/// Fails (on unix) if `n` has any interior NULs.
 pub fn unsetenv(n: &str) {
     #[cfg(unix)]
     fn _unsetenv(n: &str) {
@@ -722,10 +773,12 @@ pub fn get_exit_status() -> int {
 }
 
 #[cfg(target_os = "macos")]
-unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~str] {
+unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~[u8]] {
+    use c_str::CString;
+
     let mut args = ~[];
     for i in range(0u, argc as uint) {
-        args.push(str::raw::from_c_str(*argv.offset(i as int)));
+        args.push(CString::new(*argv.offset(i as int), false).as_bytes_no_nul().to_owned())
     }
     args
 }
@@ -736,7 +789,7 @@ unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~str] {
  * Returns a list of the command line arguments.
  */
 #[cfg(target_os = "macos")]
-fn real_args() -> ~[~str] {
+fn real_args_as_bytes() -> ~[~[u8]] {
     unsafe {
         let (argc, argv) = (*_NSGetArgc() as int,
                             *_NSGetArgv() as **c_char);
@@ -747,7 +800,7 @@ fn real_args() -> ~[~str] {
 #[cfg(target_os = "linux")]
 #[cfg(target_os = "android")]
 #[cfg(target_os = "freebsd")]
-fn real_args() -> ~[~str] {
+fn real_args_as_bytes() -> ~[~[u8]] {
     use rt;
 
     match rt::args::clone() {
@@ -756,6 +809,11 @@ fn real_args() -> ~[~str] {
     }
 }
 
+#[cfg(not(windows))]
+fn real_args() -> ~[~str] {
+    real_args_as_bytes().move_iter().map(|v| str::from_utf8_lossy(v).into_owned()).collect()
+}
+
 #[cfg(windows)]
 fn real_args() -> ~[~str] {
     use vec;
@@ -786,6 +844,11 @@ fn real_args() -> ~[~str] {
     return args;
 }
 
+#[cfg(windows)]
+fn real_args_as_bytes() -> ~[~[u8]] {
+    real_args().move_iter().map(|s| s.into_bytes()).collect()
+}
+
 type LPCWSTR = *u16;
 
 #[cfg(windows)]
@@ -803,10 +866,19 @@ extern "system" {
 
 /// Returns the arguments which this program was started with (normally passed
 /// via the command line).
+///
+/// The arguments are interpreted as utf-8, with invalid bytes replaced with \uFFFD.
+/// See `str::from_utf8_lossy` for details.
 pub fn args() -> ~[~str] {
     real_args()
 }
 
+/// Returns the arguments which this program was started with (normally passed
+/// via the command line) as byte vectors.
+pub fn args_as_bytes() -> ~[~[u8]] {
+    real_args_as_bytes()
+}
+
 #[cfg(target_os = "macos")]
 extern {
     // These functions are in crt_externs.h.
diff --git a/src/libstd/path/mod.rs b/src/libstd/path/mod.rs
index ed0ce201750..13496033fd0 100644
--- a/src/libstd/path/mod.rs
+++ b/src/libstd/path/mod.rs
@@ -578,8 +578,7 @@ impl BytesContainer for ~[u8] {
 impl BytesContainer for CString {
     #[inline]
     fn container_as_bytes<'a>(&'a self) -> &'a [u8] {
-        let s = self.as_bytes();
-        s.slice_to(s.len()-1)
+        self.as_bytes_no_nul()
     }
 }
 
diff --git a/src/libstd/rt/args.rs b/src/libstd/rt/args.rs
index cef03d66923..c417ea375fd 100644
--- a/src/libstd/rt/args.rs
+++ b/src/libstd/rt/args.rs
@@ -36,8 +36,8 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 #[cfg(test)]      pub unsafe fn cleanup() { realargs::cleanup() }
 
 /// Take the global arguments from global storage.
-#[cfg(not(test))] pub fn take() -> Option<~[~str]> { imp::take() }
-#[cfg(test)]      pub fn take() -> Option<~[~str]> {
+#[cfg(not(test))] pub fn take() -> Option<~[~[u8]]> { imp::take() }
+#[cfg(test)]      pub fn take() -> Option<~[~[u8]]> {
     match realargs::take() {
         realstd::option::Some(a) => Some(a),
         realstd::option::None => None,
@@ -47,12 +47,12 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 /// Give the global arguments to global storage.
 ///
 /// It is an error if the arguments already exist.
-#[cfg(not(test))] pub fn put(args: ~[~str]) { imp::put(args) }
-#[cfg(test)]      pub fn put(args: ~[~str]) { realargs::put(args) }
+#[cfg(not(test))] pub fn put(args: ~[~[u8]]) { imp::put(args) }
+#[cfg(test)]      pub fn put(args: ~[~[u8]]) { realargs::put(args) }
 
 /// Make a clone of the global arguments.
-#[cfg(not(test))] pub fn clone() -> Option<~[~str]> { imp::clone() }
-#[cfg(test)]      pub fn clone() -> Option<~[~str]> {
+#[cfg(not(test))] pub fn clone() -> Option<~[~[u8]]> { imp::clone() }
+#[cfg(test)]      pub fn clone() -> Option<~[~[u8]]> {
     match realargs::clone() {
         realstd::option::Some(a) => Some(a),
         realstd::option::None => None,
@@ -65,15 +65,12 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 mod imp {
     use cast;
     use clone::Clone;
-    #[cfg(not(test))] use libc;
     use option::{Option, Some, None};
     use ptr::RawPtr;
     use iter::Iterator;
-    #[cfg(not(test))] use str;
     use unstable::finally::Finally;
     use unstable::mutex::{Mutex, MUTEX_INIT};
     use mem;
-    #[cfg(not(test))] use vec;
 
     static mut global_args_ptr: uint = 0;
     static mut lock: Mutex = MUTEX_INIT;
@@ -90,15 +87,15 @@ mod imp {
         lock.destroy();
     }
 
-    pub fn take() -> Option<~[~str]> {
+    pub fn take() -> Option<~[~[u8]]> {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
             let val = mem::replace(&mut *ptr, None);
-            val.as_ref().map(|s: &~~[~str]| (**s).clone())
+            val.as_ref().map(|s: &~~[~[u8]]| (**s).clone())
         })
     }
 
-    pub fn put(args: ~[~str]) {
+    pub fn put(args: ~[~[u8]]) {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
             rtassert!((*ptr).is_none());
@@ -106,10 +103,10 @@ mod imp {
         })
     }
 
-    pub fn clone() -> Option<~[~str]> {
+    pub fn clone() -> Option<~[~[u8]]> {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
-            (*ptr).as_ref().map(|s: &~~[~str]| (**s).clone())
+            (*ptr).as_ref().map(|s: &~~[~[u8]]| (**s).clone())
         })
     }
 
@@ -126,15 +123,20 @@ mod imp {
         })
     }
 
-    fn get_global_ptr() -> *mut Option<~~[~str]> {
+    fn get_global_ptr() -> *mut Option<~~[~[u8]]> {
         unsafe { cast::transmute(&global_args_ptr) }
     }
 
     // Copied from `os`.
     #[cfg(not(test))]
-    unsafe fn load_argc_and_argv(argc: int, argv: **u8) -> ~[~str] {
+    unsafe fn load_argc_and_argv(argc: int, argv: **u8) -> ~[~[u8]] {
+        use c_str::CString;
+        use {vec, libc};
+        use vec::CloneableVector;
+
         vec::from_fn(argc as uint, |i| {
-            str::raw::from_c_str(*(argv as **libc::c_char).offset(i as int))
+            let cs = CString::new(*(argv as **libc::c_char).offset(i as int), false);
+            cs.as_bytes_no_nul().to_owned()
         })
     }
 
@@ -149,7 +151,7 @@ mod imp {
             // Preserve the actual global state.
             let saved_value = take();
 
-            let expected = ~[~"happy", ~"today?"];
+            let expected = ~[bytes!("happy").to_owned(), bytes!("today?").to_owned()];
 
             put(expected.clone());
             assert!(clone() == Some(expected.clone()));
@@ -179,15 +181,15 @@ mod imp {
     pub fn cleanup() {
     }
 
-    pub fn take() -> Option<~[~str]> {
+    pub fn take() -> Option<~[~[u8]]> {
         fail!()
     }
 
-    pub fn put(_args: ~[~str]) {
+    pub fn put(_args: ~[~[u8]]) {
         fail!()
     }
 
-    pub fn clone() -> Option<~[~str]> {
+    pub fn clone() -> Option<~[~[u8]]> {
         fail!()
     }
 }