Add os:unsetenv/1

New BIF os:unsetenv/1 which deletes an environment variable and
returns 'true'.

Does not change any old functionality.

Calls the libc function unsetenv(3) on UNIX and
SetEnvironmentVariableW(key, NULL) on Windows. The unicode support
is the same as for os:getenv and os:putenv.

8 files changed, 78 insertions, 4 deletions

diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index dc8e9101de..6037c08dd8 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -572,6 +572,7 @@ bif erlang:float_to_binary/2
 bif erlang:binary_to_float/1
 
 bif io:printable_range/0
+bif os:unsetenv/1
 
 #
 # Obsolete
diff --git a/erts/emulator/beam/erl_bif_os.c b/erts/emulator/beam/erl_bif_os.c
index 1062d4379b..e07c622928 100644
--- a/erts/emulator/beam/erl_bif_os.c
+++ b/erts/emulator/beam/erl_bif_os.c
@@ -180,3 +180,25 @@ BIF_RETTYPE os_putenv_2(BIF_ALIST_2)
     BIF_RET(am_true);
 }
 
+BIF_RETTYPE os_unsetenv_1(BIF_ALIST_1)
+{
+    char *key_buf;
+    char buf[STATIC_BUF_SIZE];
+
+    key_buf = erts_convert_filename_to_native(BIF_ARG_1,buf,STATIC_BUF_SIZE,
+					      ERTS_ALC_T_TMP,0,0,NULL);
+    if (!key_buf) {
+	BIF_ERROR(BIF_P, BADARG);
+    }
+
+    if (erts_sys_unsetenv(key_buf)) {
+	if (key_buf != buf) {
+	    erts_free(ERTS_ALC_T_TMP, key_buf);
+	}
+	BIF_ERROR(BIF_P, BADARG);
+    }
+    if (key_buf != buf) {
+	erts_free(ERTS_ALC_T_TMP, key_buf);
+    }
+    BIF_RET(am_true);
+}
diff --git a/erts/emulator/beam/sys.h b/erts/emulator/beam/sys.h
index 9561c0be96..d22f125945 100644
--- a/erts/emulator/beam/sys.h
+++ b/erts/emulator/beam/sys.h
@@ -750,6 +750,8 @@ int erts_sys_getenv(char *key, char *value, size_t *size);
 int erts_sys_getenv_raw(char *key, char *value, size_t *size);
 /* erts_sys_getenv__() is only allowed to be used in early init phase */
 int erts_sys_getenv__(char *key, char *value, size_t *size);
+/* erst_sys_unsetenv() returns 0 on success and a value != 0 on failure. */
+int erts_sys_unsetenv(char *key);
 
 /* Easier to use, but not as efficient, environment functions */
 char *erts_read_env(char *key);
diff --git a/erts/emulator/sys/unix/sys.c b/erts/emulator/sys/unix/sys.c
index 401b37b9d2..61f9f6a59a 100644
--- a/erts/emulator/sys/unix/sys.c
+++ b/erts/emulator/sys/unix/sys.c
@@ -2489,6 +2489,16 @@ erts_sys_getenv(char *key, char *value, size_t *size)
     return res;
 }
 
+int
+erts_sys_unsetenv(char *key)
+{
+    int res;
+    erts_smp_rwmtx_rwlock(&environ_rwmtx);
+    res = unsetenv(key);
+    erts_smp_rwmtx_rwunlock(&environ_rwmtx);
+    return res;
+}
+
 void
 sys_init_io(void)
 {
diff --git a/erts/emulator/sys/win32/sys_env.c b/erts/emulator/sys/win32/sys_env.c
index 754f4c6e4c..9f977ad6c8 100644
--- a/erts/emulator/sys/win32/sys_env.c
+++ b/erts/emulator/sys/win32/sys_env.c
@@ -141,6 +141,24 @@ void fini_getenv_state(GETENV_STATE *state)
     erts_smp_rwmtx_runlock(&environ_rwmtx);

 }

 

+int erts_sys_unsetenv(char *key)

+{

+    int res = 0;

+    WCHAR *wkey = (WCHAR *) key;

+

+    SetLastError(0);

+    erts_smp_rwmtx_rlock(&environ_rwmtx);

+    GetEnvironmentVariableW(wkey,

+                            NULL,

+                            0);

+    if (GetLastError() != ERROR_ENVVAR_NOT_FOUND) {

+        res = (SetEnvironmentVariableW(wkey,

+                                       NULL) ? 0 : 1);

+    }

+    erts_smp_rwmtx_runlock(&environ_rwmtx);

+    return res;

+}

+

 char*

 win_build_environment(char* new_env)

 {

diff --git a/erts/emulator/test/bif_SUITE.erl b/erts/emulator/test/bif_SUITE.erl
index 02c6de8cb1..8b612a145c 100644
--- a/erts/emulator/test/bif_SUITE.erl
+++ b/erts/emulator/test/bif_SUITE.erl
@@ -388,8 +388,12 @@ os_env(Config) when is_list(Config) ->
 	      false -> ?line ok;
 	      BadVal -> ?line ?t:fail(BadVal)
 	  end,
-    %% os:putenv and os:getenv currently uses a temp buf of size 1024
-    %% for storing key+value
+    ?line true = os:putenv(EnvVar1, "mors"),
+    ?line true = os:unsetenv(EnvVar1),
+    ?line false = os:getenv(EnvVar1),
+    ?line true = os:unsetenv(EnvVar1), % unset unset variable
+    %% os:putenv, os:getenv and os:unsetenv currently use a temp
+    %% buffer of size 1024 for storing key+value
     ?line os_env_long(1010, 1030, "hej hopp").
     
 os_env_long(Min, Max, _Value) when Min > Max ->
@@ -398,7 +402,7 @@ os_env_long(Min, Max, Value) ->
     ?line EnvVar = lists:duplicate(Min, $X),
     ?line true = os:putenv(EnvVar, Value),
     ?line Value = os:getenv(EnvVar),
-    ?line true = os:putenv(EnvVar, ""),
+    ?line true = os:unsetenv(EnvVar),
     ?line os_env_long(Min+1, Max, Value).
 
 otp_7526(doc) ->    
diff --git a/lib/kernel/doc/src/os.xml b/lib/kernel/doc/src/os.xml
index 5e182de41d..9122267c40 100644
--- a/lib/kernel/doc/src/os.xml
+++ b/lib/kernel/doc/src/os.xml
@@ -177,6 +177,17 @@ format_utc_timestamp() ->
       </desc>
     </func>
     <func>
+      <name name="unsetenv" arity="1"/>
+      <fsummary>Delete an environment variable</fsummary>
+      <desc>
+	<p>Deletes the environment variable <c><anno>VarName</anno></c>.</p>
+	<p>If Unicode filename encoding is in effect (see the <seealso
+	marker="erts:erl#file_name_encoding">erl manual
+	page</seealso>), the string (<c><anno>VarName</anno></c>) may
+	contain characters with codepoints > 255.</p>
+      </desc>
+    </func>
+    <func>
       <name name="version" arity="0"/>
       <fsummary>Return the Operating System version</fsummary>
       <desc>
diff --git a/lib/kernel/src/os.erl b/lib/kernel/src/os.erl
index ded03361ee..9415593485 100644
--- a/lib/kernel/src/os.erl
+++ b/lib/kernel/src/os.erl
@@ -26,7 +26,7 @@
 
 %%% BIFs
 
--export([getenv/0, getenv/1, getpid/0, putenv/2, timestamp/0]).
+-export([getenv/0, getenv/1, getpid/0, putenv/2, timestamp/0, unsetenv/1]).
 
 -spec getenv() -> [string()].
 
@@ -58,6 +58,12 @@ putenv(_, _) ->
 timestamp() ->
     erlang:nif_error(undef).
 
+-spec unsetenv(VarName) -> true when
+      VarName :: string().
+
+unsetenv(_) ->
+    erlang:nif_error(undef).
+
 %%% End of BIFs
 
 -spec type() -> {Osfamily, Osname} when