git oneliners

git log # shows the hashes of all commits
git reset --hard <hash of the commit to reset to>

add to .gitignore
git rm --cached files/to/remove  # starting from $GIT_DIR not /

find . -name .DS_Store -type f -exec git rm {} \;

add line

.DS_Store

to .gitignore and add the file to tracking if its not already

git add .gitignore
git commit -m ".DS_Store banished!"

git config --global core.excludesfile = /Users/username/.gitignore

add line

.DS_Store

to the .gitignore-file from the first command