Keeping two Git branches different by one file

I am certain two branches of my Git repo should only ever be different in a single file. The simplest way to ensure this is to do all work in branch1, and merge it into branch2 whenever I switch to it (wrapped into开发者_StackOverflow中文版 a shell script, so I only need one command per switch). However, is there a way to do this with even less work?

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Yes, use a git filter driver, with a smudge script intelligent enough to:

• recognize it is dealing with that single file (reminder: such a script only deals with file content, not filename)
• put the right content depending on the current branch.

But the question is: do you need two branches at all?
If this is a config file, as mentioned in "Git: how maintain (mostly) parallel branches with only a few difference?", storing templates might be better. That same question proposes other alternatives.