help with git filter-branch

Hi,

I am trying to use the script found on the following page: http://ebixio.com/blog/2009/10/15/git-filter-branch-incantations/

The idea is to add a missing parent to a certain commit. I wrote the following bash script:

#!/bin/sh
die () {
    echo >&2 "$@"
    exit 1
}
[ "$#" -eq 3 ] || die "usage: add_parent <commit_to_update>
<present_parent> <parent_to_add>"
git filter-branch --parent-filter \
    'test $GIT_COMMIT = $1 && \
    echo "-p $2 -p $3" \
    || cat' \
    --tag-name-filter 'cat' \
    $2..master

When I try to use it an a test repository, I get the following error:

./add_parent.sh ad12d20974cad91ddedd055f5335b7471e48dd1d 1541f3ae456556edc7e15cead1ae76f470961be0 88b5d6f190f9d7135148c67c4d949c0c06e179ff Rewrite ad12d20974cad91ddedd055f5335b7471e48dd1d (1/1)test: 3: =: argument expected

I am using git version 1.7.0.2.

Any help appreciated! Thank you Yann