A script to download macOS install image and create an install disk image

download_macos_and_create_install_disk.sh

#!/usr/bin/env bash

set -e

VOLUME_PATH=/Volumes/installer
while getopts ":d:h" opts; do
  case $opts in
    d)
      VOLUME_PATH=$OPTARG
      ;;
    h)
      echo "Usage: $0 [-h] [-d disk] name"
      echo "name is either mojave, mojave_beta, catalina, catalina_beta, bigsur, bigsur_beta, monterey, monterey_beta, ventura, or ventura_beta"
      echo "    -h Show this help message"
      echo "    -d /Volumes path to where it makes a bootable disk."
      echo "       If it doesn't exist, it will create a disk image."
      exit 0
      ;;
  esac
done
readonly VOLUME_PATH

shift $((OPTIND - 1))
readonly NAME=$1

if [[ $(dirname "$VOLUME_PATH") != "/Volumes" ]]; then
  echo "Invalid volume path '$VOLUME_PATH'" >&2
  exit 1
fi

case $NAME in
  highsierra)
    INSTALL_APP_PATH="/Applications/Install macOS High Sierra.app"
    MAC_APP_STORE_ID="id1246284741"
    DISK_IMAGE_SIZE="8G"
    ;;
  mojave)
    INSTALL_APP_PATH="/Applications/Install macOS Mojave.app"
    MAC_APP_STORE_ID="id1398502828"
    DISK_IMAGE_SIZE="8G"
    DOWNLOAD_ASSETS=1
    ;;
  mojave_beta)
    INSTALL_APP_PATH="/Applications/Install macOS Mojave Beta.app"
    MAC_APP_STORE_ID="id1354523149"
    DISK_IMAGE_SIZE="8G"
    REQUIRE_ENROLL=1
    DOWNLOAD_ASSETS=1
    ;;
  catalina)
    INSTALL_APP_PATH="/Applications/Install macOS Catalina.app"
    MAC_APP_STORE_ID="id1466841314"
    DISK_IMAGE_SIZE="10G"
    DOWNLOAD_ASSETS=1
    ;;
  catalina_beta)
    INSTALL_APP_PATH="/Applications/Install macOS Catalina Beta.app"
    MAC_APP_STORE_ID="id1455661060"
    DISK_IMAGE_SIZE="10G"
    REQUIRE_ENROLL=1
    DOWNLOAD_ASSETS=1
    ;;
  bigsur)
    INSTALL_APP_PATH="/Applications/Install macOS Big Sur.app"
    MAC_APP_STORE_ID="id1526878132"
    DISK_IMAGE_SIZE="10G"
    DOWNLOAD_ASSETS=1
    ;;
  bigsur_beta)
    INSTALL_APP_PATH="/Applications/Install macOS Big Sur Beta.app"
    BUNDLE_ID="com.apple.InstallAssistant.Seed.macOS1016Seed1"
    DISK_IMAGE_SIZE="10G"
    REQUIRE_ENROLL=1
    DOWNLOAD_ASSETS=1
    ;;
  monterey)
    INSTALL_APP_PATH="/Applications/Install macOS Monterey.app"
    MAC_APP_STORE_ID="id1576738294"
    DISK_IMAGE_SIZE="14G"
    DOWNLOAD_ASSETS=1
    ;;
  monterey_beta)
    INSTALL_APP_PATH="/Applications/Install macOS Monterey Beta.app"
    MAC_APP_STORE_ID="id1556159220"
    BUNDLE_ID="com.apple.InstallAssistant.Seed.macOS12Seed1"
    DISK_IMAGE_SIZE="14G"
    REQUIRE_ENROLL=1
    DOWNLOAD_ASSETS=1
    ;;
  ventura)
    INSTALL_APP_PATH="/Applications/Install macOS Ventura.app"
    MAC_APP_STORE_ID="id1638787999"
    DISK_IMAGE_SIZE="14G"
    DOWNLOAD_ASSETS=1
    ;;
  ventura_beta)
    INSTALL_APP_PATH="/Applications/Install macOS Ventura Beta.app"
    MAC_APP_STORE_ID="id1616785793"
    BUNDLE_ID="com.apple.InstallAssistant.Seed.macOS13Seed1"
    DISK_IMAGE_SIZE="14G"
    REQUIRE_ENROLL=1
    DOWNLOAD_ASSETS=1
    ;;
  *)
    echo "Unknown name '$NAME'. See usage by give -h." >&2
    exit 1
    ;;
esac
readonly INSTALL_APP_PATH
readonly MAC_APP_STORE_ID
readonly BUNDLE_ID
readonly DISK_IMAGE_SIZE
readonly REQUIRE_ENROLL
readonly DOWNLOAD_ASSETS

if [[ -r "$INSTALL_APP_PATH/Contents/SharedSupport/InstallESD.dmg" || \
      -r "$INSTALL_APP_PATH/Contents/SharedSupport/SharedSupport.dmg" ]]; then
  echo "Found the install app, create an install disk."
  if [[ ! -e $VOLUME_PATH ]]; then
    readonly DISK_IMAGE_NAME=$(basename "$VOLUME_PATH")

    echo "Creating a disk image '$DISK_IMAGE_NAME' size $DISK_IMAGE_SIZE"

    hdiutil create -o "$DISK_IMAGE_NAME.dmg" -volname "$DISK_IMAGE_NAME" -size $DISK_IMAGE_SIZE -layout SPUD -fs HFS+J && \
    hdiutil attach "$DISK_IMAGE_NAME.dmg"
  fi

  ARGS=(--volume ${VOLUME_PATH})
  if ((DOWNLOAD_ASSETS)); then
    ARGS=("${ARGS[@]}" --downloadassets)
  fi
  readonly ARGS

  # Create an install disk.
  sudo "$INSTALL_APP_PATH/Contents/Resources/createinstallmedia" "${ARGS[@]}"
else
  if ((REQUIRE_ENROLL)); then
    echo "Enroll developer seed and open Mac App Store."
    echo "You can unenroll after downloading the install app by next command:"
    echo "sudo /System/Library/PrivateFrameworks/Seeding.framework/Versions/A/Resources/seedutil unenroll"

    # Tell Mac App Store that we've enrolled `DeveloperSeed`.
    # Actual `enroll` is needed to download a complete install image from Mac App Store.
    sudo /System/Library/PrivateFrameworks/Seeding.framework/Versions/A/Resources/seedutil enroll DeveloperSeed
    /usr/libexec/PlistBuddy -c "clear dict" -c "add :SeedProgram string DeveloperSeed" /Users/Shared/.SeedEnrollment.plist
  fi

  if [[ ! -z $BUNDLE_ID ]]; then
    # Open Preferences to download macOS installer app.
    /usr/bin/open "x-apple.systempreferences:com.apple.preferences.softwareupdate?client=bau&installMajorOSBundle=$BUNDLE_ID"
    echo "Click Download to download installer app, then run this script again to create an install disk image."
  elif [[ ! -z $MAC_APP_STORE_ID ]]; then
    # Open Mac App Store to download macOS installer app.
    /usr/bin/open "macappstores://itunes.apple.com/app/$MAC_APP_STORE_ID"
    echo "Click Get on Mac App Store to download installer app, then run this script again to create an install disk image."
  else
    echo "Mising both Bundle ID and Mac App Store ID." >&2
    exit 1
  fi
fi

Thank you for publishing this script!
It was necessary to add the option -volname $DISK_IMAGE_NAME to hdiutil create when using under conditions where the volume does not exist.

Ah, actually it's default to untitled but if not, it should given. Let me change it.

not sure if this will be useful to you but after the journey i went on to find them i wanted to share them with someone. here are the Bundle IDs for some MacOS non beta versions

com.apple.InstallAssistant.Catalina
com.apple.InstallAssistant.macOSVentura
com.apple.InstallAssistant.macOSBigSur
com.apple.InstallAssistant.macOSMonterey

i was able to find these based on what i read here https://pspdfkit.com/guides/ios/faq/finding-the-app-bundle-id/

On any recent new macOS, likely using softwareupdate command would be better solution to download installer. For example,

$ softwareupdate --list-full-installers
$ softwareupdate --fetch-full-installer --full-installer-version 14.0