Sets up a git repo with a particular branch layout. Use it to play with merging vs rebasing

make_git_test_tree.sh

# make_git_test_tree.sh
#
# This script sets up a git repository with a particular branch layout. Playing around with rebasing and merging
# the branches should help your understanding of git.
#
# Make sure you're in a goddamned empty directory when you execute this script. The script
# shouldn't be in the same directory.
#
# Here's an example, assuming this file is in the current working directory:
#
# > mkdir gittest
# > cd gittest
# > ../make_git_test_tree.sh
# 
rm -rf muhfiles .git

git init

function make_commit {  
  GIT_COMMIT_NAME=$1
  echo "Making commit $GIT_COMMIT_NAME"
  touch muhfiles/$GIT_COMMIT_NAME && git add muhfiles/$GIT_COMMIT_NAME && git commit -a -m "$GIT_COMMIT_NAME"
}

# Make the repo. It looks like this:
#
# master A -- B -- C -- D
#              \
# topic1        M -- N -- O
#                     \
# topic2               X -- Y
#
mkdir muhfiles

make_commit A
make_commit B
git checkout -b topic1

make_commit M
make_commit N

git checkout -b topic2
make_commit X
make_commit Y

git checkout topic1
make_commit O

git checkout master
make_commit C
make_commit D

# Rebase topic2 onto master. 
git checkout topic2
git rebase master

# Now it looks like this, where the ' indicates new commit hashes that were generated by rebase.
# PRO-TIP, you don't want to be in this state EVAR:
#
# master A -- B -- C ------ D
#              \             \
# topic1        M -- N -- O   \
#                              \
# topic2                        M' -- N' -- X' -- Y'
#

Oops...fix in dox suggested by @sphing.