From af6948afe004b03e5d919a3c0a0fefd08937b463 Mon Sep 17 00:00:00 2001
From: Tim Morgan <tim@timmorgan.org>
Date: Fri, 13 Sep 2019 07:42:47 -0500
Subject: [PATCH] Shell: fix crash when using `cd -` and OLDPWD is null

---
 Shell/main.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Shell/main.cpp b/Shell/main.cpp
index ebf5b1c78f..57acffdd6e 100644
--- a/Shell/main.cpp
+++ b/Shell/main.cpp
@@ -85,6 +85,8 @@ static int sh_cd(int argc, char** argv)
     } else {
         if (strcmp(argv[1], "-") == 0) {
             char* oldpwd = getenv("OLDPWD");
+            if (oldpwd == nullptr)
+                return 1;
             size_t len = strlen(oldpwd);
             ASSERT(len + 1 <= PATH_MAX);
             memcpy(pathbuf, oldpwd, len + 1);