auto import from //depot/cupcake/@135843
diff --git a/libc/stdlib/setenv.c b/libc/stdlib/setenv.c
new file mode 100644
index 0000000..856db5e
--- /dev/null
+++ b/libc/stdlib/setenv.c
@@ -0,0 +1,105 @@
+/* $OpenBSD: setenv.c,v 1.9 2005/08/08 08:05:37 espie Exp $ */
+/*
+ * Copyright (c) 1987 Regents of the University of California.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in the
+ * documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the University nor the names of its contributors
+ * may be used to endorse or promote products derived from this software
+ * without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <stdlib.h>
+#include <string.h>
+
+char *__findenv(const char *name, int *offset);
+
+extern char **environ;
+
+/*
+ * setenv --
+ * Set the value of the environmental variable "name" to be
+ * "value". If rewrite is set, replace any current value.
+ */
+int
+setenv(const char *name, const char *value, int rewrite)
+{
+ static char **lastenv; /* last value of environ */
+ char *C;
+ int l_value, offset;
+
+ if (*value == '=') /* no `=' in value */
+ ++value;
+ l_value = strlen(value);
+ if ((C = __findenv(name, &offset))) { /* find if already exists */
+ if (!rewrite)
+ return (0);
+ if ((int)strlen(C) >= l_value) { /* old larger; copy over */
+ while ((*C++ = *value++))
+ ;
+ return (0);
+ }
+ } else { /* create new slot */
+ size_t cnt;
+ char **P;
+
+ for (P = environ; *P != NULL; P++)
+ ;
+ cnt = P - environ;
+ P = (char **)realloc(lastenv, sizeof(char *) * (cnt + 2));
+ if (!P)
+ return (-1);
+ if (lastenv != environ)
+ memcpy(P, environ, cnt * sizeof(char *));
+ lastenv = environ = P;
+ offset = cnt;
+ environ[cnt + 1] = NULL;
+ }
+ for (C = (char *)name; *C && *C != '='; ++C)
+ ; /* no `=' in name */
+ if (!(environ[offset] = /* name + `=' + value */
+ malloc((size_t)((int)(C - name) + l_value + 2))))
+ return (-1);
+ for (C = environ[offset]; (*C = *name++) && *C != '='; ++C)
+ ;
+ for (*C++ = '='; (*C++ = *value++); )
+ ;
+ return (0);
+}
+
+/*
+ * unsetenv(name) --
+ * Delete environmental variable "name".
+ */
+int
+unsetenv(const char *name)
+{
+ char **P;
+ int offset;
+
+ while (__findenv(name, &offset)) /* if set multiple times */
+ for (P = &environ[offset];; ++P)
+ if (!(*P = *(P + 1)))
+ break;
+
+ return 0;
+}