How to derive application build version string with Git's `describe` command?

Question

I want to compose application build version that is automatically derived from the Git branch name I am on (when building) and the number of commits since the branch has div

Answer 1

git describe --long would always output version number like this: v1.2-10-gdeadbee, which means 10th commit since annotated tag 'v1.2' that points at commit with shortened SHA-1 'deadbee'. So all you have to do is to tag branch start (branching point of a branch) e.g. <branch>-start.

The abbreviated commit SHA-1 hash is required to distinguish between ambiguous situations, because "3rd commit since tag 'x'" (for example) does not uniquely distinguish a commit; there can be more than one commit that fits mentioned description in the presence of nonlinear, branchy development. For example in the situation shown on the ASCII-art diagram below both commits marked with * fits "3rd commit since tag 'x'" description.

          /-.---*---.-\                   
         /             \                  
.---x---.---.---*---.---M---.    <--- branch

_{Note that in "merged in" case as shown above you can't use branch name to distinguish between those two commits with the same description.}

So what you have to do would be to take git describe --long output (the --long option is here to avoid ambiguities with parsing, see git describe manpage), parse it, and add current branch info (from e.g. git symbolic-ref HEAD, not from pasing git branch output) yourself.