savage_squash.sh

#!/usr/bin/env bash

set -e

if [[ $1 == '' ]]
then
    echo 'please provide a branch name to savagely squash from'
    echo 'exiting'
    exit 1
fi

latest_rebase_target_branch_commit=$(git log $1 --format=format:%H | sed -n 1p)
latest_and_historical_commits=$(git log --format=format:%H)

depth=0
depth_check=1

for commit in $latest_and_historical_commits
do
    if [[ $commit == $latest_rebase_target_branch_commit ]]
        break
    then
        ((depth++))
    fi
done

if [[ $depth -eq $depth_check ]]
then
    echo 'you are only one commit ahead'
    echo 'amending existing commit instead..'
else
    soft_reset_depth=$(($depth - $depth_check))

    if [[ $soft_reset_depth < 1 ]]
    then
        echo 'no changes compared to $1 branch'
        echo 'exiting..'
        exit 1
    fi

    echo "soft reseting back by $soft_reset_depth commits"
    git reset -soft HEAD~$soft_reset_depth
fi

git commit --all --amend --no-edit

echo "$depth comit(s) amended - history is now altered"
echo 'you may now push with force'