Easy and safe git squash with no manual calculations

git-squash.sh

#!/bin/sh

git status --branch --untracked-files=no --porcelain=2 | (
  while IFS=' .' read -r _s _b _name _value; do
    [ "$_s" = "#" ] || break
    if [ "$_b" = "branch" ]; then
      case "$_name" in
      head|upstream|ab)
        eval "_$_name='$_value'"
        ;;
      esac
    fi
  done
  [ "$(( ${_ab%\ *} ))" = "$(( $_ab ))" ] || {
    echo "Your copy behind $_upstream by $(( -1 * ${_ab#* } )) commit(s)! Fetch first!"
    return 1
  } >&2
  echo "Squashing $_head..$_upstream [$_ab]"
  git rebase -i "HEAD~$(( ${_ab%\ *} ))"
)