How do you manage your development site URLs/links?

Hello, for those who manage separate development sites, how to you manage it? Subdomain? or a subfolder within your main domain? Or as a completely separate domain?

I have a large custom built html/php website (8,195 physical files, 96 folders, and many dynamically generated pages) and have been managing it as a completely separate domain. I used to update everything direct on the live site when I had less traffic, but today, I can no longer 'experiment' with features and have to keep it a separate dev site, but I'm struggling to manage it. The main reason is if I update my dev file, I then have to copy that file to my local files for the real website, then search/replace the dev domain name to the real domain name, then copy to the live server. And if I update multiple files, it gets complicated and is easy to forget to copy over one of the updated files- especially when buried in multiple folders. All the files are 1.3 GB, so I can't copy all and do a massive search/replace for all each time, but just those that change. It seems like a messy solution and there has got to be a better way. I do have a main include.php file where I can change the domain name variable from dev to real, but I have globals off for security reasons and that include file is not included in all files, many have the variable stored within its own file, hence the search/replace each time.

How do you manage your development site? Any recommendations?

subfolder within your main domain would be good to manage with same server.

Surprised no one else pitched in...

I just hide the files extensions within the name of the site I'm working on, so if I was building xyzderp.com I'd do most of the development at xyzderp.com/r4nd0mth1nlyveiledn4me - throw <meta name="robots" content="noindex, nofollow"> in there immediately and go, go, go.