error in rewriting author history with filter-branch --env-filter

[Adam Mercer <ramercer@gmail.com>]

Hi

I'm trying to use git filter-branch to rewrite the author information
on an repo that was imported from CVS a while ago, the commits I'm
trying to rewrite are as follows:

commit 2cdeb25148f02b35391bd80a2c4c1876d7b8b840
Author: <ram>
Date:   Wed Dec 22 13:36:01 2004 +0000

    modify style

I'm trying to modify <ram> to be replaced with my name and email
address. To do this I've been trying to use the following command

$ git filter-branch --env-filter '
an="$GIT_AUTHOR_NAME"
am="$GIT_AUTHOR_EMAIL"
if [ "$GIT_AUTHOR_EMAIL" = "ram"]; then
an="Adam Mercer"
am="ramercer@gmail.com"
fi
export GIT_AUTHOR_NAME=$an
export GIT_AUTHOR_EMAIL=$am
'

however when I run this I get loads of errors of the form:

Rewrite 18242fa722ff393e7fce78e05f37fa7c3b3825e1
(1/216)/opt/local/libexec/git-core/git-filter-branch: line 307: [:
missing `]'

Any ideas what I'm doing wrong? I'm running git-1.6.2.2.

Cheers

Adam