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


** 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. 



** See Also **


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


** Description **

Git is popular version control system designed to handle very large projects
with speed and efficiency; it is used mainly for various open source projects,
most notably the Linux kernel.


Branches in git are kind of like variables in Tcl.  When one makes a commit,
one creates a commit object, that "contains" the parent commit(s) and a
directory tree specifying the current state of one's working directory, kind of
like:

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


(Rather than referencing things with pointers to [Tcl_Obj]s however, things are
referenced with 160-bit [sha1] hashes.) Deleting a branch is like unsetting a
variable: if that variable held the only reference to a particular value
(commit), then the commit is gone too, but if anything else held another
reference (e.g., it was merged into another branch, which results in a commit
with more than one parent), then the commit is still there.

Of course, since all of it is stored on disk, it would be impractical to use a
refcount scheme to reclaim unused memory. Instead git has a garbage collector
git-gc. Until that is run, deleted commits (and whatever) can still be accessed
by giving explicit hash numbers.

----

[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].

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