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

+ + + +

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