'''[http://git-scm.com%|%git]''' is a ''Fast Distributed Version Control System'' (DVCS).



** See Also **

   [git timestamps]:   [RJM] 2010-10-05: A page regarding an attempt to allow timestamp preservation of files



** Criticism **

   ''I don't think trying to understand any other VCS in terms of git is a good idea.  Git is so horribly unintuitive and dependent on its internal data structure model that it's a losing proposition.'':   - mst, on git and [fossil], [Tcl Chatroom], 2013-12-15



** Critique **

   [https://sqlite.org/whynotgit.html%|%Why SQLite Does Not Use Git]:   

   [https://stevebennett.me/2012/02/24/10-things-i-hate-about-git/%|%10 things I hate about Git], Steve Bennett, 2012-02-24:   The most damning point is number 7, '''Unsafe Version Control'''.  A bad actor can irrevocably destroy the contents of a repository.   [Fossil] doesn't have this hole.



** Lore **

   [https://www.linuxjournal.com/content/git-origin-story%|%A Git Origin Story] {Zack Brown} {2018 07 27}:   How and why git came to be.



** Packages **

   [lg2]:   Tcl bindings to the https://libgit2.org%|%libgit2%|% library.



** Tools **

   [gitk]:   a history visualization tool written in Tcl/Tk.

   [http://core.tcl.tk/akupries/fossil2git/home%|%fossil2git]:   Support scripts to maintain a system for mirroring a set of [fossil] repositories to one or more git repositories. 

   [https://github.com/AngryLawyer/mug%|%mug]:   A [Teacup] workalike that can download git repositories.



** Description **

Git is a distributed version control system created by [Linus Torvalds] over
the course of a few weeks for developing the [Linux] kernel after [Larry McVoy]
revoked the custom license for [BitKeeper] for the project in response to an
attempt by [Andrew Tridgell] to reverse-engineer the BitKeeper network
protocols. It uses the filesystem as its database, and outperforms every other
distributed version control system in terms of speed.

In git, a branch is named a sequence change sets.  Each change set is
represented by a '''commit object''' that references the parent commit(s) and a
'''tree object''' that describes the data in the directory hierarchy.

======
proc commit {} {
    upvar #0 $::current_branch current
    set current [list commit $::current_tree $current]
}
======

Each object is referenced by its [sha1] hash.  Thus, even if two different
commit objects reference the same tree, that tree object is only store once.
Since tree object is recursive, and each subtree is itself a tree object, each
subtree is only stored once, even if it is part of multiple trees.

Git does not use reference counting to reclaim orphaned objects.  Instead
git-gc, the garbage collector git-gc deletes them when it is run.  Until then,
any object that has been deleted can be reclaimed.

----

[Zarutian] 2007-07-16:  Can git be obtained or compiled into a multiplatform
starkit?  Hard when one has only an thumbdrive/ipod to store stuff.

[Lars H] 2008-06-05: Since it's a Unixy collection of many programs that do one
thing each, I suspect this would be tricky (can't `[exec]` something in a [vfs],
can you?). Apparently there has been some work
[http://git.or.cz/gitwiki/SoC2007Projects#head-f604c29a605c7c5fe1e993ef5aa74ce34f3fb84e]
on turning it into a library, but that only got part of the way.

Makes me wonder, though… Could there be a semi-automatic way of turning a suite
of C programs (like git, or at least the git plumbing) into a [load]able
extension which exposes each program as a Tcl command? (I expect one would have
to do things like turning static C variables into fields of some dynamically
allocated struct, to ensure reentrancy, but C is not my forte.)

FWIW, I later noticed that git has a concept of '''builtin''' command, with
something rather close to a Tcl_CmdProc for every built-in subcommand of git.
Probably not too hard to wrap manually, provided the built-in commands don't
try to exec each other.

----

A thing that seems to be special about git is that it tracks content (e.g.
procedure definitions) rather than files (as [CVS], [SVN], and [Mercurial]
does).  See
[http://wincent.com/a/about/wincent/weblog/archives/2007/07/a_look_back_bra.php%|%A look back: Bram Cohen vs Linus Torvalds].

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