Git: Need cross-branch version number

I would like to generate a simple, increasing version integer, based on when a commit has changed a certain folder. And, I want this version number to be valid across branches.

To illustrate, suppose the folder is named FOO, and it is on BRANCH1 and BRANCH2开发者_如何学C. Let's say version V is currently equal to 10.

1) make a commit that modifies FOO on BRANCH1: I would like V = 11 2) now make a commit that modifies FOO on BRANCH2: I would like V = 12

Any help would be greatly appreciated! Jacko

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Branches are mere pointers on a graph.

git describe remains the only "label" valid across repos.
This question has an example where git describe is used to generate a "Vxxx".

You also have git name-rev if you want a "label" relative to a branch (but not valid across repos).