Make macOS shell run in parity with Linux

bootstrap-mac-linux-parity.sh

#!/usr/bin/env bash
set -euo pipefail

log() {
  printf '\n[%s] %s\n' "$(date '+%H:%M:%S')" "$*"
}

append_if_missing() {
  local file="$1"
  local line="$2"

  touch "$file"
  if ! grep -Fqx "$line" "$file"; then
    printf '%s\n' "$line" >> "$file"
  fi
}

detect_brew_prefix() {
  if [[ -x /opt/homebrew/bin/brew ]]; then
    echo "/opt/homebrew"
  elif [[ -x /usr/local/bin/brew ]]; then
    echo "/usr/local"
  else
    echo ""
  fi
}

ensure_homebrew() {
  if ! command -v brew >/dev/null 2>&1; then
    echo "Homebrew is required but not installed."
    echo "Install it first from https://brew.sh and re-run this script."
    exit 1
  fi
}

main() {
  ensure_homebrew

  local brew_bin
  brew_bin="$(command -v brew)"
  local brew_prefix
  brew_prefix="$(brew --prefix)"

  log "Updating Homebrew"
  brew update

  log "Installing Linux-parity CLI packages"
  brew install \
    bash \
    coreutils \
    findutils \
    gawk \
    gnu-getopt \
    gnu-sed \
    gnu-tar \
    grep \
    make \
    diffutils \
    less \
    ed \
    watch \
    jq

  log "Upgrading existing formulae"
  brew upgrade

  log "Ensuring modern Bash is listed in /etc/shells"
  local bash_path
  bash_path="$(brew --prefix)/bin/bash"
  if ! grep -Fxq "$bash_path" /etc/shells 2>/dev/null; then
    echo "Adding $bash_path to /etc/shells, sudo may prompt once."
    printf '%s\n' "$bash_path" | sudo tee -a /etc/shells >/dev/null
  fi

  if [[ "${SHELL:-}" != "$bash_path" ]]; then
    log "Switching default shell to Homebrew Bash"
    chsh -s "$bash_path" || true
  fi

  log "Configuring shell startup files"
  local zprofile="$HOME/.zprofile"
  local zshrc="$HOME/.zshrc"
  local bash_profile="$HOME/.bash_profile"
  local bashrc="$HOME/.bashrc"

  append_if_missing "$zprofile" 'eval "$(/opt/homebrew/bin/brew shellenv 2>/dev/null || /usr/local/bin/brew shellenv)"'
  append_if_missing "$bash_profile" '[[ -f ~/.bashrc ]] && source ~/.bashrc'

  local parity_block_start="# >>> linux-parity-bootstrap >>>"
  local parity_block_end="# <<< linux-parity-bootstrap <<<"

  local parity_block
  parity_block=$(cat <<'EOF'
# >>> linux-parity-bootstrap >>>
export HOMEBREW_NO_AUTO_UPDATE=1

if command -v brew >/dev/null 2>&1; then
  eval "$(brew shellenv)"

  PATH="$(brew --prefix coreutils)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix findutils)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix gnu-sed)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix gawk)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix grep)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix make)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix gnu-tar)/libexec/gnubin:$PATH"
  PATH="$(brew --prefix gnu-getopt)/bin:$PATH"

  MANPATH="$(brew --prefix coreutils)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix findutils)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix gnu-sed)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix gawk)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix grep)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix make)/libexec/gnuman:${MANPATH:-}"
  MANPATH="$(brew --prefix gnu-tar)/libexec/gnuman:${MANPATH:-}"
fi

export NVM_DIR="$HOME/.nvm"
if [[ -s "$(brew --prefix nvm 2>/dev/null)/nvm.sh" ]]; then
  . "$(brew --prefix nvm)/nvm.sh"
elif [[ -s "$NVM_DIR/nvm.sh" ]]; then
  . "$NVM_DIR/nvm.sh"
fi
# <<< linux-parity-bootstrap <<<
EOF
)

  for rc in "$zshrc" "$bashrc"; do
    touch "$rc"
    if ! grep -Fq "$parity_block_start" "$rc"; then
      printf '\n%s\n' "$parity_block" >> "$rc"
    fi
  done

  log "Running brew cleanup"
  brew cleanup

  log "Basic verification"
  echo "brew: $(brew --version | head -n 1)"
  echo "bash: $("$bash_path" --version | head -n 1)"
  echo "sed:  $(sed --version 2>/dev/null | head -n 1 || true)"
  echo "awk:  $(awk --version 2>/dev/null | head -n 1 || true)"
  echo "make: $(make --version | head -n 1)"
  echo "tar:  $(tar --version | head -n 1)"
  echo "find: $(find --version 2>/dev/null | head -n 1 || true)"

  cat <<EOF

Done.

Next steps:
1. Open a new terminal session.
2. Verify:
   which bash sed awk make tar find
3. Expected:
   bash -> $brew_prefix/bin/bash
   sed/awk/make/tar/find should resolve to Homebrew GNU versions first.

Note:
- BSD and Apple tools still exist on the system.
- This script makes GNU tools win via PATH, which is the safest parity model.
- If your repos hardcode /bin/bash, update those shebangs to /usr/bin/env bash.
EOF
}

main "$@"