Creates alias `git squash` for simple sequential commit squashing

squash-commits.sh

#!/bin/bash

# description:
# creates git alias 'squash' that squashes the last n commits with a new commit message
# 
# usage: 
# `git squash <n> "<commit-message>"` e.g. `git squash 3 "feat(scope): my new feature"`
# or
# `git squash -n <n> -m "<commit-message>"` e.g. `git squash -n 3 -m "feat(scope): my new feature"`
#
# params:
# <n> number of commits to squash (including current commit)
# <commit-message> the new commit message for the squashed commit
#
# executed commands:
# - validates input parameters
# - checks if enough commits exist to squash
# - resets soft to go back n commits (keeping changes staged)
# - commits with the new message
#
# assumptions:
# - you are in the root directory of the repository
# - you are on the correct branch
# - the number provided includes the most recent/current commit
#
# create alias:
# save this file and run `chmod +x squash-commits.sh && ./squash-commits.sh`

git config --global alias.squash '! _() {
  # Parse arguments
  if [ "$1" = "-n" ]; then
    # Flag-based syntax: git squash -n 5 -m "message"
    if [ -z "$2" ] || [ -z "$4" ] || [ "$3" != "-m" ]; then
      echo "Usage: git squash -n <number> -m \"<commit-message>\""
      return 1
    fi
    num_commits="$2"
    commit_message="$4"
  else
    # Positional syntax: git squash 5 "message"
    if [ -z "$1" ] || [ -z "$2" ]; then
      echo "Usage: git squash <number> \"<commit-message>\""
      echo "   or: git squash -n <number> -m \"<commit-message>\""
      return 1
    fi
    num_commits="$1"
    commit_message="$2"
  fi
  
  # Validate that num_commits is a positive integer
  if ! [[ "$num_commits" =~ ^[1-9][0-9]*$ ]]; then
    echo "Error: Number of commits must be a positive integer"
    return 1
  fi
  
  # Check if we have enough commits to squash
  commit_count=$(git rev-list --count HEAD)
  if [ "$num_commits" -gt "$commit_count" ]; then
    echo "Error: Cannot squash $num_commits commits, only $commit_count commits exist"
    return 1
  fi
  
  # Check if repository is clean (no uncommitted changes)
  if ! git diff-index --quiet HEAD --; then
    echo "Warning: You have uncommitted changes. They will be included in the squashed commit."
    read -p "Continue? (y/N): " -n 1 -r
    echo
    if [[ ! $REPLY =~ ^[Yy]$ ]]; then
      echo "Aborted."
      return 1
    fi
  fi
  
  echo "Squashing last $num_commits commits with message: \"$commit_message\""
  
  # Reset to n commits back, keeping changes staged
  git reset --soft HEAD~"$num_commits" &&
  
  # Commit with the new message
  git commit -m "$commit_message" &&
  
  echo "✓ Successfully squashed $num_commits commits!"
}; _'

echo "Git alias 'squash' has been created successfully!"
echo ""
echo "Usage examples:"
echo "  git squash 3 \"feat(auth): add user authentication\""
echo "  git squash -n 5 -m \"refactor: optimize database queries\""
echo ""
echo "Note: This will squash the last n commits (including the current one) into a single commit."