ash: restore value of imported variable on unexport

Shell variables imported from the environment are marked with a
special flag and backslashes in their values are (by default)
replaced with forward slashes.  Sometimes this may not be what
we want.

Modify the 'export' shell built-in so unexporting a variable of
this type restores its original value from the environment and
removes its special flag.  It can then be re-exported.

Adds 32 bytes.

(GitHub issue #428)

1 files changed, 9 insertions, 0 deletions

diff --git a/shell/ash.c b/shell/ash.c
index d9ab3feb5..64a8dd318 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -15512,6 +15512,15 @@ exportcmd(int argc UNUSED_PARAM, char **argv)
                                                 }
 #endif
                                                 vp->flags = ((vp->flags | flag) & flag_off);
+#if ENABLE_PLATFORM_MINGW32
+                                                /* Unexporting a variable imported from the
+                                                 * environment restores its original value and
+                                                 * removes the VIMPORT flag. */
+                                                if ((vp->flags & VIMPORT) && (flag_off == ~VEXPORT)) {
+                                                        vp->flags &= ~VIMPORT;
+                                                        p = getenv(name);
+                                                } else
+#endif
                                                 continue;
                                         }
                                 }