Making Git retain different section content between branches

I'm developing a Userscript that my employers have asked me to begin to manage via Git.

Right now, I have a stable file and a beta file, so that everyone in the organization can install the stable code but can choose to help test the beta additions instead, if they want. Some portions of that file should remain different, the content and changes should not be merged between branches.

For example, if I convert the Beta file to a Git Branch, and later decide that the Beta changes are stable and merge the Beta back into the Stable code (which will not have changed) the Git Merge process as I understand it will "helpfully" update the Stable Greasemonkey definition headers based on whatever values are on those lines in the Beta branch. This is thoroughly undesirable, as these headers contain an auto-update URL that Greasemonkey will check for updates.

// ==UserScript== (stable)
// @downloadURL  --  StableURL File Location
// ==/UserScript==

// ==UserScript== (beta)
// @downloadURL  --  BetaURL File Location
// ==/UserScript==

>Git Merge<

// ==UserScript== (stable)
// @downloadURL  --  BetaURL File Location
// ==/UserScript==

I want to retain the ability to have distinct URLs between the Beta code and the Stable code, but have not been able to identify a method to make Git's merge process ignore the lines that Greasemonkey needs to do its thing properly, but if I don't have the Beta as a separate Branch, I'm not sure how to use Git to easily migrate changed code from Beta to Stable, which is the stated reason for asking me to adopt Git functionality. (Well, the other reason is to make it easier for others to contribute to and identify the history of the project...)

Any help is much appreciated.

All your changes should be merged except changes to those values, which makes them not like the others, not changes to intrinsic content but deployment-specific changes. Those might be best applied in the post-checkout hook. Here's a sample, a per-branch include processor

cat <<\EOF >.git/hooks/post-checkout
#!/bin/sh
if branch=`git symbolic-ref HEAD --short -q`; then
    for file in `git ls-files -cix*.@branch`; do
        echo "* making ${file%.@branch} from $file with branch-specific includes"
        echo '/^@include-branch-specific ([a-z/]*)$/ { s//cat \1.'$branch'/e }' \
        | sed -rf- $file >${file%.@branch}
    done
fi
EOF
chmod +x .git/hooks/post-checkout

# testing
git checkout beta

cat  <<\EOF >config.@branch
// ==UserScript==
@include-branch-specific config
// ==/UserScript==
EOF

echo >config.stable '// @downloadURL  --  StableURL File Location'
echo >config.beta   '// @downloadURL  --  BetaURL File Location'

git add config.*
# git rm --cached config
git commit -m'setting up per-branch configs'
git checkout

git checkout stable
git cherry-pick beta
git checkout

In your repository, create three files, called header.master, header.branch and main.js. Then you can keep different versions of main.js in different branches, but keep the header files the same - one for each branch, and all header files will be in all branches.

Make a build script, called build.sh, which looks like this:

#! /bin/sh
cat header.$(git rev-parse --abbrev-ref HEAD) main.js >myscript.js

Either users must run your build script, or you must provide the prebuilt user script yourself - but I guess you are already doing the latter, since you have a download URL!

You could write a custom merge driver for git, and configure git to use it - but this would probably be more trouble than it's worth.