Plumbing 2: alternate-history.rb

Table of Contents

1 Step 1: Reading

Read section 10.3 of the git book.

You are responsible for memorizing the meaning/use of the folowing commands:

git commit-tree
git update-ref

2 Step 3: Write the code

Write a script called alternate-history. This script will take a series of trees and an output branch name. It will create a alternate fake history starting with the first tree, going to the second, etc. The fake history will be placed in a branch with the given name. Use commit-tree and update-ref to do this - don't do sketchy things like checkout multiple file versions.

Here's an example of me using my solution

~/git/js-parsons % alternate-history.rb -t cafd0d12 -t e6ab292b -o alternative-history-branch
~/git/js-parsons % git checkout alternative-history-branch
Switched to branch 'alternative-history-branch'
~/git/js-parsons % git log
commit 5906ac134394e23e7279690c188e521d12097f16
Author: Buffalo <>
Date:   Sun Mar 13 23:20:05 2016 -0400

    alternative followup

commit 750a0189cb8479e4571af7f0b4a44e9ff8500a69
Author: Buffalo <>
Date:   Sun Mar 13 23:20:05 2016 -0400

    alternative begin

~/git/js-parsons % git cat-file -p 5906ac13
tree e6ab292b8cb583d454f0e215311d15dfceb7bf33
parent 750a0189cb8479e4571af7f0b4a44e9ff8500a69
author Buffalo <> 1457925605 -0400
committer Buffalo <> 1457925605 -0400

alternative followup
~/git/js-parsons % git cat-file p 750a0189c
fatal: invalid object type "p"
~/git/js-parsons % git cat-file -p 750a0189c
tree cafd0d121d20251e1a60df8e4f4d99edb3d1840e
author Buffalo <> 1457925605 -0400
committer Buffalo <> 1457925605 -0400

alternative begin
~/git/js-parsons %

If you like, I've provided a start here:


3 Step 4: Turn-in

You will turn in via Moodle. You must turn in 2 things:

  1. The source code of your script
  2. The a text file running a command similar to the one above, switching to the created branch, looking at the long, and then using git cat-file to dump all the commits (so I can see the trees are correct). Use this command on js-parsons:
alternate-history.rb -t 4a218e805a4b -t cafd0d12 -t e6ab292b -o alternative-history-branch

Author: Buffalo, Rose-Hulman Institute of Technology

Created: 2016-03-13 Sun 23:36

Emacs 24.5.1 (Org mode 8.2.10)