two branches: keep one difference but merge others forth and back

Hi,

Is this possible.

I'd like to have two branches.

If possible I would be able to merge forth and back between both of them.

However I would like, that certain differences will be kept between both branches.

Is there any way to tell git to permanently ignoring certain commits from merging?

Example:
---------
   Normally shell scripts would have a first line of
'#!/bin/bash',
but in a certain branch I would like that the first lines would be

'#!/usr/local/bin/bash'

All from then on however I'd like to be able to commit on both branches and to merge from the other branches (and always keep this difference)

What I tried:
-------------
My first naive approach was:
- create shell scripts in master,
- create then a branch named 'my_shell'
- modify first lines of shell scripts in this branch and commit
- checkout master
- merge my_shell to master with merge strategy 'ours'
  git pull my_shell -s ours
- now I changed something else in master
- when I try to merge back to branch my_shell I will not only get
  the most recent changes done in master, but I will also undo the
changes in line 1 of my shell scripts.

So it seems I am not doing things as one should.

Potential other strategies:
----------------------------
- never commit anything on branch my_shell and just pull regularly
  from master to keep it synced.

- commit changes / bug fixes also on branch my_shell, but NEVER merge
back to master. If a change grom my_shell is really needed on master,
then just cherry-pick.

Thanks in advance for suggestions how you would deal with such 'situations'

On Sun, Nov 27, 2011 at 06:31:42PM +0100, Gelonida N wrote:

This goes against what a merge is.

If you tell git to merge, it expects that you want to take the changes done in the other branch.

You can amend the merge (or the next merge) commit so you undo that change. Git should leave that line alone as long as you don't change it.

Or you could have a branch where you make changes and two branches where you change the hashbang. Merging from the main branch into the specific branches won't touch the hashbang, as long as you don't touch it.

   cmn

On Sun, Nov 27, 2011 at 18:31, Gelonida N <gelonida@gmail.com> wrote:

Instead of merging, you could use rebasing. So you have one development branch where you do all the changes, and then another branch where the only commit there is that special difference (as in your /usr/bin/bash example). From then on you only develop/maintain the original branch, and then you rebase the 'special' branch on top of the development branch. Then you get all the updates, plus your special change applied on top each time. Likewise, if you have two variants (say, one /bin/bash, another /usr/bin/bash, and then one with /usr/local/bin/bash) then create two branches and rebase them on top of the third branch (the development branch) every time you wish to deploy new updates.

-Tor