Is bash in OSX case-insensitive? Are bash commands on OSX case insensitive? I type "which TR" and it shows /usr/bin/TR, though there is no such binary there. Same thing for other binaries, when capitalized. Or is Terminal.app maybe doing this translation? How do I turn this off?
This is actually a feature of the filesystem of your disk, not bash or Terminal.app.

HFS+ (the Mac filesystem) is usually configured to be case insensitive but case preserving. This means that the file system will consider foo and FoO to be the same, but when you create a new file it will remember which letters where capitalized and which were not.

When you format a disk with HFS+ you can chose whether the file system should case sensitive or not. If you chose to format with UFS (Unix FileSystem) it is always case sensitive, AFAIK.

To check whether a disk is case sensitive, run:

 diskutil info &lt;device&gt;


For example:

 diskutil info disk0s2


Look for the Name: line. If it reads something like Mac OS Extended (Case-sensitive, Journaled) it means that it is case-sensitive. If it just reads Mac OS Extended (without the Case-sensitive) then it is only case preserving but not case sensitive.