[PATCH 4/4] filter-branch: fix variable export logic

filter-branch tries to restore "old" copies of some
environment variables by using the construct:

  unset var
  test -z "$old_var" || var="$old_var" && export var

However, by the short-circuit logic, we will always run
'export var'. On bash and dash, exporting an unset variable
has no effect. However, on some shells (such as FreeBSD's
/bin/sh), the shell exports the empty value.

This manifested itself in this case as git-filter-branch
setting GIT_INDEX_FILE to the empty string, which in turn
caused its call to git-read-tree to fail, leaving the
working tree pointing at the original HEAD instead of the
rewritten one.

To fix this, we change the short-circuit logic to better
match the intent:

  test -z "$old_var" || { var="$old_var" && export var; }

Signed-off-by: Jeff King <redacted>
---
 git-filter-branch.sh |   10 +++++-----
 1 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 333f6a8..0304dc5 100755
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh

@@ -435,11 +435,11 @@ rm -rf "$tempdir"
 trap - 0
 
 unset GIT_DIR GIT_WORK_TREE GIT_INDEX_FILE
-test -z "$ORIG_GIT_DIR" || GIT_DIR="$ORIG_GIT_DIR" && export GIT_DIR
-test -z "$ORIG_GIT_WORK_TREE" || GIT_WORK_TREE="$ORIG_GIT_WORK_TREE" &&
-	export GIT_WORK_TREE
-test -z "$ORIG_GIT_INDEX_FILE" || GIT_INDEX_FILE="$ORIG_GIT_INDEX_FILE" &&
-	export GIT_INDEX_FILE
+test -z "$ORIG_GIT_DIR" || { GIT_DIR="$ORIG_GIT_DIR" && export GIT_DIR; }
+test -z "$ORIG_GIT_WORK_TREE" || { GIT_WORK_TREE="$ORIG_GIT_WORK_TREE" &&
+	export GIT_WORK_TREE; }
+test -z "$ORIG_GIT_INDEX_FILE" || { GIT_INDEX_FILE="$ORIG_GIT_INDEX_FILE" &&
+	export GIT_INDEX_FILE; }
 git read-tree -u -m HEAD
 
 exit $ret

-- 
1.5.5.1.296.gf618c