gitfun.sh

#!/usr/bin/env bash

export DIR=$(mktemp -d)
cd $DIR

git init
git config commit.gpgsign false
git config user.name Someone
git config user.email someone@example.com
export GIT_AUTHOR_DATE="2000-01-01T12:34:56"
export GIT_COMMITTER_DATE="2000-01-01T12:34:56"

echo -e 'change M1\n' > foo
git add foo
git commit -m 'root, change M1'

echo -e 'change M2\n' >> foo && git commit -am 'change M2'

git switch -c feature-a

echo -e 'change A1\n' >> foo && git commit -am 'change A1'

echo -e 'change A2\n' >> foo && git commit -am 'change A2'

echo -e 'change A3\n' >> foo && git commit -am 'change A3'

git switch main

echo -e 'change M3\n' >> foo && git commit -am 'change M3'

git switch feature-a

echo
git log --oneline --graph --all
echo
echo Agenda:
echo  1. stacked branches
echo  2. absorb and interactive rebase
echo  3. upstream rebase
echo  4. update and push stack
echo

exec $SHELL

echo "Exited interactive shell. If you did not intend to do this you can go into the
test repo using the current shell with:

cd $DIR"

# 1. stacked branches
#   * git branch -f pr-1 @~~
#   * git branch -f pr-2 @~
#   * git log --oneline --graph --all
# 2. absorb and interactive rebase
#   * make changes
#   * git add and absorb
#   * git rebase --autosquash --interactive --keep-base main
# 3. upstream rebase
#   * git rebase --update-refs main
# 4. update and push stack
#   * git log --pretty='format:%D' main.. | cut -d' ' -f3
#   * git log --pretty='format:%D' main.. | cut -d' ' -f3 | xargs git push --set-upstream --force-with-lease --force-if-includes origin
# 5. [bonus] git trim

Execute the script to start the demo. Presenter's notes are the comment at the bottom and map onto the printed instructions.

Important message to get across: Set appropriate defaults for these flags in gitconfig, and otherwise create some aliases.

The mentioned git absorb tool (automatic fixup generation).

Aliases for step 4:

# to tell if its master/main reliably
main = "!f() {if git remote | grep -qE '.+'; then git symbolic-ref refs/remotes/origin/HEAD --short | cut -d/ -f2; else echo main fi}; f"
# force push whole stack, I only ever use this to push
puf = "!git stack | xargs git push --set-upstream --force-with-lease --force-if-includes origin"
# prints the current stack
stack = "!git for-each-ref --format='%(refname:short)' refs/heads/ --merged HEAD --no-merged $(git main) --sort=committerdate"