Git Is Not Magic

I'm bored. Let's make a git repository out of whole cloth.

Git repos are stored in .git:

fakegit$ mkdir .git
-

They have a “symbolic ref” (which are text files, see man -git-symbolic-ref) named HEAD, pointing -to the currently checked-out branch. Let's use master. Branches are refs -under refs/heads (see man git-branch):

fakegit ((unknown))$ echo 'ref: refs/heads/master' > .git/HEAD
-

The have an object database and a refs database, both of which are simple -directories (see man -gitrepository-layout and man -gitrevisions). Let's also enable the reflog, -because it's a great safety net if you use history-editing tools in git:

fakegit ((ref: re...))$ mkdir .git/refs .git/objects .git/logs
-fakegit (master #)$
-

Now __git_ps1, at least, is convinced that we have a working git repository. -Does it work?

fakegit (master #)$ echo 'Hello, world!' > hello.txt
-fakegit (master #)$ git add hello.txt
-fakegit (master #)$ git commit -m 'Initial commit'
-[master (root-commit) 975307b] Initial commit
-1 file changed, 1 insertion(+)
-create mode 100644 hello.txt
-
-fakegit (master)$ git log
-commit 975307ba0485bff92e295e3379a952aff013c688
-Author: Owen Jacobson <owen.jacobson@grimoire.ca>
-Date:   Wed Feb 6 10:07:07 2013 -0500
-
-    Initial commit
-

Eeyup.

Should you do this? Of course not. Anywhere you could run these commands, -you could instead run git init or git clone, which set up a number of -other structures, including .git/config and any unusual permissions options. -The key part here is that a directory's identity as “a git repository” is -entirely a function of its contents, not of having been blessed into being by -git itself.

You can infer a lot from this: for example, you can infer that it's “safe” to -move git repositories around using FS tools, or to back them up with the same -tools, for example. This is not as obvious to everyone as you might hope; people

- - - -

- - -comments powered by Disqus -

- - - - - -