git-squash-with-reset.sh

# Fresh repo and some master history
git init squash
cd squash/
echo one > a
git add .
git commit -m "First commit"
echo two >> a
git commit -m "Second commit"
git commit -am "Second commit"

# Here we start working on a branch
git checkout -b branch
echo three >> a
git commit -am "Branch first"
echo four > b
git add .
git commit -m "Branch second"

# Precaution - save the current tip
git tag branch_before_sqaush

# Finally, the actual sqaush
git reset master
git add .
git commit -am "Branch squashed commit"