_GIT_INDEX_OUTPUT: allow plumbing to output to an alternative index file.

diff --git a/Documentation/git.txt b/Documentation/git.txt
index 9defc332736e1b6297ac003e491706d5ce32e834..8fa1a0a58827e84b884d6c997686564dae1a6a58 100644 (file)
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -315,6 +315,14 @@ git so take care if using Cogito etc.
        index file. If not specified, the default of `$GIT_DIR/index`
        is used.
 
+'_GIT_INDEX_OUTPUT'::
+       When this environment is defined, plumbing level
+       commands that update the index writes the resulting
+       index to this file, instead of `$GIT_INDEX_FILE` (or its
+       default `$GIT_DIR/index`).  This is solely meant to be
+       used by Porcelain to drive low-level plumbing.  Defining
+       this in user's environment is always an error.
+
 'GIT_OBJECT_DIRECTORY'::
        If the object storage directory is specified via this
        environment variable then the sha1 directories are created