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

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The thing you have you to understand about git is that branches are essentially merely commit bookmarks. The fact that you were on the foo branch when you made the 0deadbeef commit is immaterial to the commit itself; the branch is not part of its identity.

(Mercurial bakes the branch name into the commit. In a variety of ways, this is inferior, as Dustin Sallings explains.)

Even assuming that git describe would just use the currently checked out branch – if you have a mergy history, there could be multiple paths leading to the same most recent tagged commit that git describe would use. So there isn’t even necessarily any one branch.

Another note: you may object that even if “3rd commit from tag X” is ambiguous in the general case, git describe could just look at the graph and figure out whether it is ambiguous and if not, leave out the hash. However, there is nothing stopping anyone starting a branch on top of that tag at a later time – so then your describe string would become ambiguous retrospectively.

Bottom line is that the only unambiguous identifier of a commit is its hash. So that must be in there. What git describe does is add some redundant (and in case of the commit number, ambiguous) information that makes the description more useful to the kind of spatial/relational comprehension that humans orient themselves with, within the confines of the Git model.

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