Apple - How to check if my HD is case sensitive or not?

You can use terminal to read the File System Personality:

diskutil info /

Look for the fields named below:

   File System Personality:  Journaled HFS+
   Type (Bundle):            hfs
   Name (User Visible):      Mac OS Extended (Journaled)

If the file system is case sensitive, you will see Case-sensitive Journaled HFS in the first pasted line and Mac OS Extended (Case-sensitive, Journaled) in the third.

Disk Utility will also show you this from the info window for any File System it can see.

Something like this should work:

Testing

touch abc1
touch abC1
ls ab*

Interpreting Results

• 1 file - case insensitive
• 2 files - case sensitive

Update for El Capitan, see the attached screen shot from Disk Utility's Info-window.