Allow nil value in setenv.

* sysif.c (setenv_wrap): If value is nil, and overwrite is
missing or t, call unsetenv.

* txr.1: Documented.

1 files changed, 6 insertions, 2 deletions

diff --git a/sysif.c b/sysif.c
index 3b8341cc..d0a06ca0 100644
--- a/sysif.c
+++ b/sysif.c
@@ -703,8 +703,12 @@ val getenv_wrap(val name)
 static val setenv_wrap(val name, val value, val overwrite)
 {
   char *nameu8 = utf8_dup_to(c_str(name));
-  char *valu8 = utf8_dup_to(c_str(value));
-  setenv(nameu8, valu8, default_arg(overwrite, t) != nil);
+  char *valu8 = value ? utf8_dup_to(c_str(value)) : 0;
+  int ovw = default_arg(overwrite, t) != nil;
+  if (valu8)
+    setenv(nameu8, valu8, ovw);
+  else if (ovw)
+    unsetenv(nameu8);
   free(valu8);
   free(nameu8);
   return value;