Bash script to squash all commits in the current branch (against master)

squash-all

#!/usr/bin/env bash
# squash-all [BASE_BRANCH]

PROG="${0##*/}"
DIR="${0%/*}"

talk() { echo 1>&2 "$*" ; }
vtalk() { (( verbose )) && talk "$*" ; }
error() { talk "$*" ; exit 1 ; }

usage() { 
  (( $# > 0 )) && talk "$*"
  cat 1>&2 <<USAGE
usage: $PROG [options] [BASE_BRANCH [BRANCH_NAME]]

This script will squash all the commits in BRANCH_NAME, if given.  If
not given the current branch in the current workding directory is used.

If BASE_BRANCH is given, then it is used as the base-branch for the merge
that squashes the commits in the target branch.  If BASE_BRANCH is not
given, "master" is assumed.

Unless -a is given, confirmation of actions is confirmed with a prompt
to the user for a yes or no answer.

Options:
  -a     go ahead; do the change
  -h     show this help
  -n     don't do any changes, but show the commands
  -v     be verbose
USAGE
  exit
}

run() {
  if [[ -n "$norun" ]]; then
    talk "(norun) $@"
  else
    safe_run "$@"
  fi
  return 0
}

safe_run() {
  if [[ -n "$verbose$norun" ]]; then
    talk ">> $@"
  fi
  if ! eval "$@" ; then
    code=$?
    return $code
  fi
  return 0
}

set_branch() {
  if [[ -n "$1" ]] ; then
    branch_name="$1"
  else
    branch_name=`current_branch`
  fi
}

current_branch() {
  if [[ -z "$current_branch" ]] ; then
   current_branch="$(git rev-parse --abbrev-ref HEAD)"
  fi
  echo "$current_branch"
}

set_base_branch() {
  base_branch="${1:-master}"
}

validate_branch_name() {
  if [[ -z "$branch_name" ]]; then
    echo "No branch name! (detached HEAD?)"
    exit
  fi
}

validate_base_branch() {
  case "$base_branch" in
    master|mast|m)          base_branch=master ;;
    releases|release|rel|r) base_branch=releases ;;
    *) error "Only 'releases' or 'master' can be used as a base branch!" ;;
  esac
}

confirm_go_ahead() {
  while (( ! go_ahead )) ; do
    talk "Branch '${branch_name}' will be merged with '${base_branch}'" 
    talk " .. and all local commits squashed"
    read -p "Okay? [yN]" ans
    ans="${ans:-no}"
    case "${ans,,}" in
      yes|ye|y) go_ahead=1 ;;
      no|n)     error "Nothing done." ;;
      *)        talk "Please answer yes or no, or just <return> for 'no'" ;;
    esac
  done
}

get_merge_base_commit() {
  vtalk "Computing common base commit for $base_branch and $branch_name .."
  safe_run "git merge-base '$base_branch' '$branch_name'"
}

squash_commits() {
  local base_commit="$1"
  run "git reset --soft $base_commit && git commit -a"
}

maybe_checkout_branch() {
  if [[ "$branch_name" != `current_branch` ]] ; then
    vtalk "Checking out $branch_name."
    run "git checkout $branch_name"
  fi
}

##################################################

go_ahead= norun= verbose=

while getopts 'ahnv' opt ; do
  case "$opt" in
    h) usage ;;
    a) go_ahead=1 ;;
    n) norun=1 ;;
    v) vebose=1 ;;
  esac
done
shift $(( OPTIND - 1 ))

(( $# > 2 )) && usage "Too many arguments!"

set_base_branch "$1"
set_branch "$2"

validate_branch_name
validate_base_branch
confirm_go_ahead

set -x

maybe_checkout_branch
merge_base_commit=`get_merge_base_commit`
squash_commits $merge_base_commit

exit