rsnext/packages/create-next-app/helpers/get-pkg-manager.ts

export type PackageManager = 'npm' | 'pnpm' | 'yarn'

export function getPkgManager(): PackageManager {
  const userAgent = process.env.npm_config_user_agent

  if (userAgent) {
    if (userAgent.startsWith('yarn')) {
      return 'yarn'
    } else if (userAgent.startsWith('pnpm')) {
      return 'pnpm'
    } else {
      return 'npm'
    }
  } else {
    return 'npm'
  }
}