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

This is just wrong.  AND-list and OR-list operators && and || have equal
precedence and they bind left to right.  The second term, var="$old"
assignment always succeeds, so we always end up exporting 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 <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/git-filter-branch.sh b/git-filter-branch.sh
index 333f6a8f3b783d46a0ce3b2f59bae152936cd11c..80e99e539477cbd7266b19c1bd90d424cf1341ee 100755 (executable)
--- a/git-filter-branch.sh
+++ b/git-filter-branch.sh
@@ -435,11 +435,17 @@ 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" &&
+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" &&
+}
+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