Reuse GIT_WORK_TREE in post-receive hook to rm a few files

I've used this 'tutorial' to set up a DSP environment: http://toroid.org/ams/git-website-howto (Yes, I don't have a T).

My workflow is very easy:

1. Develop locally (D)
2. Commit a few things
3. Commit more things
4. Push to Staging (and Github) (S)
5. Test new code on Staging
6. Push to Production (P)

My code contains CSS files that are minified by my code and then saved to 1 file: all.css. Locally, I've turned that option off, so I don't have to manually remove all.css all the time every time I change my CSS. On both Staging and Production, they should cache as soon as possible (so create all.css from the separate CSS files).

The problem is every time I push, I have to remove all.css (and all.js -- same exact story) to see the changes (and properly test).

From the tutorial I made a post-receive hook that checks out the changes into a certain folder (where Apache reads the code).

My current post-receive hook:

#!/bin/sh
GIT_WORK_TREE=/var/www/www.example.org git checkout -f

I want to reuse $GIT_WORK_TREE to remove two files within $GIT_WORK_TREE (being www/all.css and www/all.js), but I can't... There's no var $GIT_WORK_TREE on the next line.

So I changed it to this, but I don't like that, especially if I want to do more with it in the future:

#!/bin/sh
GIT_WORK_TREE=/var/www/www.example.org git checkout -f
rm /var/www/www.example.org/www/all.css
rm /var/www/www.example.org/www/all.js

$GIT_WORK_TREE is NOT reused like this.

Things I've tried that don't work:

GIT_WORK_TREE=/var/www/www.example.org git checkout -f
rm $GIT_WORK_TREE/www/all.css
rm $GIT_WORK_TREE/www/all.js

rm: file doesn't exist etc (/www/all.css) ($GIT_WORK_TREE is empty)

GIT_WORK_TREE=/var/www/www.example.org
git checkout -f

fatal: this operation must be run in a work tree

GIT_WORK_TREE=/var/www/www.example.org
cd $GIT_WORK_TREE
git checkout -f

fatal: Not in a git repository (or any .....)

I guess my problem is as much with how Bash works as it is with how GIT works =)