Unfortunately companies like Steam and Adobe have still opted not to properly update their apps to be compatible with case-sensitive file systems, so if you have opted to choose this when setting up your Mac or Hack, when you get to wanting to install Steam you'll run into issues.
Fortunately in the case of Steam there is a workaround that will let you play your favorite Steam games, even if you don't have any case-insensitive partitions available. In this quicky I'll show you how I did it. It's a little quirky, but quite easy.
Step 1: Create a Disk Image
Launch Disk Utility (if you're not familiar, you can find this in the Utilities folder within your Applications folder), and select File » New Image » Blank Image...
Save it as something memorably, such as "Steam," and select the folder you'd like to save it in. In my case I chose to store it right in my Applications folder. Before you hit save, we need to change some of the image settings.
Sparse disk image in the
Image Format selection, and
Mac OS Extended (Journaled) under
Format. Now, in
Size enter the maximum size you'd like this disk to be. Don't worry, the image won't take up that amount of space right away, it will expand as your content grows. I recommend you choose something sane. I have chosen
40 GB for my image, as I don't really play many games at all these days and mostly want Steam for the occasional indie fix. You should pick a size that works for the kinds of games you're planning to install.
With those settings in place, hit
Save and after a moment your newly created image will be ready to go. Open it if this wasn't done automatically already, and let's get to the second part.
Step 2: Install Steam.
Assuming you have already downloaded the Steam installer dmg, open it and, instead of dragging
Steam.app into your Applications folder, copy it onto the image you just created. Don't launch it just yet, we need to take one more step.
open Terminal (Applications » Utilities) or iTerm and copy/paste the following line:
mkdir /Volumes/Steam/Library && ln -s /Volumes/Steam/Library ~/Library/Application\ Support/Steam
Note: If you have called your image anything other than
Steam, you should replace that part of the above command (in both places). The rest can remain the same.
What this command does is create a shortcut from where Steam expects its Library data to exist (inside your
~/Library/Application Support folder) to where it actually resides, which is in a newly created folder called
Library on your just created disk image.
Done! You can now launch Steam from your disk image and it will work as it usually would. Any time you want to play some games, all you have to do is mount the disk image and launch Steam from there. If you drag Steam into your dock or launch it from something like Alfred you don't even have to manually mount the disk image first, macOS will automatically do this, so long as the image file is in an expected place.
While it's certainly not a perfect solution, it does work and allows you to use a case-sensitive file system, which depending on your work or personal needs might be a firm requirement for you.
A happy side effect is that it becomes easier to bring your Steam library with you, meaning you can have your one installation in this disk image and store it on an external hard drive, for example, and use it on different Macs if you have more than one.