What is the name of pointers like `HEAD~1` in git?

Question

I'm aware that HEAD~1 represents the parent of the commit HEAD is on and that HEAD^2 represents the second parent of the commit HEAD is on.

From git reflog, HEAD@{n} is a gitrevision.

Do pointers like HEAD~n, HEAD^n, HEAD~3^2, master~1, cb2510e~1 etc. have a special name? Are they references in the same way that branches point to a specific commit? Is it called a relative reference?

I've been trying to look, but have not been successful. Can anyone shed some light?

I don't think `HEAD` can be a permanent ref because it is different for every branch. — Tim Biegeleisen, Apr 06 '18 at 01:07
Possibly relevant: https://stackoverflow.com/questions/2529971/what-is-the-head-in-git — Tim Biegeleisen, Apr 06 '18 at 01:09
HEAD in more or less words just represents where you currently are in git — Andrew Kim, Apr 06 '18 at 01:10
really I just want to know if there is a "git" semantic name for pointers like `HEAD~1` — Andrew Kim, Apr 06 '18 at 01:10
The link I pasted above uses the language `pointer`, `ref`, and `symbolic ref`. — Tim Biegeleisen, Apr 06 '18 at 01:12
Ah, they are just things that are known colloquially then? thought they might have a specific name in the git vernacular, similar to a `gitrevision` — Andrew Kim, Apr 06 '18 at 01:14
Maybe it does. Git has a rather loose technical language. It is more important to just know what `HEAD` and `master~1` mean rather than what to call them. — Tim Biegeleisen, Apr 06 '18 at 01:15
^ completely agree, just putting together a lesson plan and wanted to have a definitive name, but thanks for the talk through! if anyone does know plz post answer! — Andrew Kim, Apr 06 '18 at 01:17
Note: `HEAD^2` is the second parent; `HEAD~2` is the first parent of the first parent (equivalent to `HEAD^1^1`). — torek, Apr 06 '18 at 01:25

torek · Accepted Answer · 2018-04-06T01:39:01.333

I would say that all of these are, collectively, "git revisions" (or gitrevisions as one word). Note that all of these are listed in the gitrevisions documentation.

Unfortunately, this term also seems to encompass range notations such as origin/master..master. For discussion purposes we would like to have a term that is specific to the two halves of such an expression, so as to construct a formal grammar. Git does not define one, so you must invent your own. The closest seems to be the phrase extended SHA-1 syntax, as jsageryd noted. This is a particularly poor term: despite its clumsiness, it's too specific, given that there is a long term effort to move Git from SHA-1 to some other hashing algorithm.

Internally, within the source to Git, there is a move to rename these to OID, which stands for Object IDentifier. OID seems like the most appropriate term. However, internally, this is for the fully resolved thing that is currently a 160-bit SHA-1 and will eventually be larger. Perhaps extended OID? :-)

jsageryd · Answer 2 · 2018-04-06T01:25:17.873

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A term used both in man gitrevisions and in commit messages in the Git project is "extended SHA-1 syntax".

Although, I am inclined to think that its usage is for the most part limited to technical discussions about Git internals. I may be wrong.

edited Apr 06 '18 at 01:25

answered Apr 06 '18 at 01:19

jsageryd

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score 0 · Answer 3 · answered Apr 06 '18 at 06:13

A name I saw used for them which stuck with me is "revspec" which does pair nicely with "refspec", the pairing used to describe how fetch and push should map refnames in the different repositories. I don't recall where I saw it and I don't recall ever using it, a git grep on the source says it only occurs in the sample post-receive hook, googling says others do use it.

score 0 · Answer 4 · answered Jan 28 '20 at 18:51

I tried to find out about that extended SHA-1 syntax --- but that seems to be a git thing. Maybe this is even meant with a grain of humour: the "canonical" name would be the (abrrev.) SHA-1 name. But for practical reasons you have HEAD (and @) and this extended (a bit cryptic) syntax.

"SPECIFYING REVISIONS" is the big title in gitrevisions.

A revision parameter <rev> typically, but not necessarily, names a commit object. It uses what is called an extended SHA-1 syntax. Here are various ways to spell object names. The ones listed near the end of this list name trees and blobs contained in a commit.

So HEAD~1 would be a name for (= a way to spell) a commit object, whose (real) name is "7ah25e...".

What is the name of pointers like `HEAD~1` in git?

4 Answers4